| author | ohair |
| Wed, 26 May 2010 20:28:04 -0700 | |
| changeset 5551 | 327690766109 |
| parent 5506 | 202f599c92aa |
| child 19222 | 19707772a06c |
| permissions | -rw-r--r-- |
| 2 | 1 |
<!-- |
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Copyright (c) 2005, 2006, Oracle and/or its affiliates. All rights reserved. |
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DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER. |
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This code is free software; you can redistribute it and/or modify it |
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under the terms of the GNU General Public License version 2 only, as |
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published by the Free Software Foundation. Oracle designates this |
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particular file as subject to the "Classpath" exception as provided |
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by Oracle in the LICENSE file that accompanied this code. |
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This code is distributed in the hope that it will be useful, but WITHOUT |
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ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or |
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FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License |
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version 2 for more details (a copy is included in the LICENSE file that |
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accompanied this code). |
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You should have received a copy of the GNU General Public License version |
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2 along with this work; if not, write to the Free Software Foundation, |
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Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA. |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
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Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
|
22 |
or visit www.oracle.com if you need additional information or have any |
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327690766109
6956202: Fix a few missed rebranding issues, please contact lines etc.
ohair
parents:
5506
diff
changeset
|
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questions. |
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--> |
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<html> |
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<head> |
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<style> |
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.key { color: red; font-weight: bold }
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</style> |
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<title> |
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Object Query Language (OQL) |
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</title> |
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</head> |
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<body> |
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<h1>Object Query Language (OQL)</h1> |
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<p> |
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OQL is SQL-like query language to query Java heap. OQL allows to filter/select information |
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wanted from Java heap. While pre-defined queries such as "show all instances of class X" |
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are already supported by HAT, OQL adds more flexibility. OQL is based on JavaScript expression |
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language. |
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</p> |
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<p> |
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OQL query is of the form |
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<pre> |
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<code> |
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<span class="key">select</span> <JavaScript expression to select> |
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[ <span class="key">from</span> [<span class="key">instanceof</span>] <class name> <identifier> |
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[ <span class="key">where</span> <JavaScript boolean expression to filter> ] ] |
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</code> |
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</pre> |
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where class name is fully qualified Java class name (example: java.net.URL) or array class name. |
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[C is char array name, [Ljava.io.File; is name of java.io.File[] and so on. |
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Note that fully qualified class name does not always uniquely identify a |
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Java class at runtime. There may be more than one Java class with the same |
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name but loaded by different loaders. So, class name is permitted to be |
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id string of the class object. |
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If <span class="key">instanceof</span> keyword is used, subtype objects are selected. If this |
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keyword is not specified, only the instances of exact class specified are selected. Both |
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<span class="key">from</span> and <span class="key">where</span> clauses are optional. |
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</p> |
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<p> |
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In <span class="key">select</span> and (optional) <span class="key">where</span> clauses, the expression |
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used in JavaScript expression. Java heap objects are wrapped as convenient script objects so that |
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fields may be accessed in natural syntax. For example, Java fields can be accessed with obj.field_name |
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syntax and array elements can be accessed with array[index] syntax. Each Java object selected is |
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bound to a JavaScript variable of the identifier name specified in <span class="key">from</span> clause. |
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</p> |
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<h2>OQL Examples</h2> |
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<ul> |
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<li>select all Strings of length 100 or more |
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<pre> |
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<code> |
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select s from java.lang.String s where s.count >= 100 |
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</code> |
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</pre> |
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<li>select all int arrays of length 256 or more |
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<pre> |
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<code> |
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select a from [I a where a.length >= 256 |
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</code> |
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</pre> |
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<li>show content of Strings that match a regular expression |
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<pre> |
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<code> |
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select s.value.toString() from java.lang.String s |
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where /java/(s.value.toString()) |
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</code> |
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</pre> |
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<li>show path value of all File objects |
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<pre> |
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<code</b> |
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select file.path.value.toString() from java.io.File file |
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</code> |
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</pre> |
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<li>show names of all ClassLoader classes |
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<pre> |
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<code> |
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select <a href="#classof">classof</a>(cl).name |
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from instanceof java.lang.ClassLoader cl |
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</code> |
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</pre> |
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<li>show instances of the Class identified by given id string |
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<pre> |
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<code> |
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select o from instanceof 0xd404b198 o |
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</code> |
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</pre> |
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Note that 0xd404b198 is id of a Class (in a session). This is found by |
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looking at the id shown in that class's page. |
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</ul> |
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<h2>OQL built-in objects, functions</h2> |
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<h3>heap object</h3> |
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The <b>heap</b> built-in object supports the following methods: |
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<ul> |
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<li><b>heap.forEachClass</b> -- calls a callback function for each Java Class |
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<pre> |
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<code> |
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heap.forEachClass(callback); |
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</code> |
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</pre> |
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<li><b>heap.forEachObject</b> -- calls a callback function for each Java object |
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<pre> |
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<code> |
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heap.forEachObject(callback, clazz, includeSubtypes); |
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</code> |
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</pre> |
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<code>clazz</code> is the class whose instances are selected. If not specified, defaults to java.lang.Object. <code>includeSubtypes</code> is a boolean flag |
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that specifies whether to include subtype instances or not. Default value of |
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this flag is true. |
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<a name="findClass"></a> |
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<li><b>heap.findClass</b> -- finds Java Class of given name |
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<pre> |
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<code> |
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heap.findClass(className); |
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</code> |
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</pre> |
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where <code>className</code> is name of the class to find. The resulting Class |
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object has following properties: |
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<ul> |
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<li>name - name of the class. |
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<li>superclass - Class object for super class (or null if java.lang.Object). |
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<li>statics - name, value pairs for static fields of the Class. |
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<li>fields - array of field objects. field object has name, signature |
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properties. |
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<li>loader - ClassLoader object that loaded this class. |
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<li>signers - signers that signed this class. |
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<li>protectionDomain - protection domain to which this class belongs. |
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</ul> |
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Class objects have the following methods: |
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<ul> |
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<li>isSubclassOf - tests whether given class is direct or indirect |
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subclass of this class or not. |
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<li>isSuperclassOf - tests whether given Class is direct or indirect |
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superclass of this class or not. |
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<li>subclasses - returns array of direct and indirect subclasses. |
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<li>superclasses - returns array of direct and indirect superclasses. |
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</ul> |
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<a name="findObject"></a> |
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<li><b>heap.findObject</b> -- finds object from given object id |
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<pre> |
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<code> |
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heap.findObject(stringIdOfObject); |
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</code> |
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</pre> |
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<a name="classes"></a> |
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<li><b>heap.classes</b> -- returns an enumeration of all Java classes |
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<a name="objects"></a> |
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<li><b>heap.objects</b> -- returns an enumeration of Java objects |
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<pre> |
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<code> |
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heap.objects(clazz, [includeSubtypes], [filter]) |
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</code> |
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</pre> |
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<code>clazz</code> is the class whose instances are selected. If not specified, defaults to java.lang.Object. <code>includeSubtypes</code> is a boolean flag |
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that specifies whether to include subtype instances or not. Default value of |
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this flag is true. This method accepts an optional filter expression to filter |
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the result set of objects. |
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<a name="finalizables"></a> |
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<li><b>heap.finalizables</b> -- returns an enumeration of Java objects that are |
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pending to be finalized. |
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<li><b>heap.livepaths</b> -- return an array of paths by which a given object |
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is alive. This method accepts optional second parameter that is a boolean |
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flag. This flag tells whether to include paths with weak reference(s) or not. |
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By default, paths with weak reference(s) are not included. |
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<pre> |
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<code> |
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select heap.livepaths(s) from java.lang.String s |
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</code> |
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</pre> |
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Each element of this array itself is another array. The later array is |
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contains an objects that are in the 'reference chain' of the path. |
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<li><b>heap.roots</b> -- returns an Enumeration of Roots of the heap. |
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<a name="rootobj"></a> |
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Each Root object has the following properties: |
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<ul> |
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<li>id - String id of the object that is referred by this root |
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<li>type - descriptive type of Root (JNI Global, JNI Local, Java Static etc) |
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<li>description - String description of the Root |
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<li>referrer - Thread Object or Class object that is responsible for this root or null |
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</ul> |
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</ul> |
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Examples: |
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<ul> |
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<li>access static field 'props' of class java.lang.System |
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<pre> |
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<code> |
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select heap.findClass("java.lang.System").statics.props
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select heap.findClass("java.lang.System").props
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</code> |
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</pre> |
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<li>get number of fields of java.lang.String class |
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<pre> |
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<code> |
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select heap.findClass("java.lang.String").fields.length
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</code> |
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</pre> |
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<li> find the object whose object id is given |
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<pre> |
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<code> |
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select heap.findObject("0xf3800b58")
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</code> |
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</pre> |
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<li>select all classes that have name pattern java.net.* |
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<pre> |
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<code> |
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select <a href="#filter">filter</a>(heap.classes(), "/java.net./(it.name)") |
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</code> |
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</pre> |
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</ul> |
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<h3>functions on individual objects</h3> |
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<ul> |
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<li><a href="#allocTrace">allocTrace(jobject)</a> |
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<li><a href="#classof">classof(jobject)</a> |
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<li><a href="#forEachReferrer">forEachReferrer(callback, jobject)</a> |
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<li><a href="#identical">identical(o1, o2)</a> |
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<li><a href="#objectid">objectid(jobject)</a> |
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<li><a href="#reachables">reachables(jobject, excludedFields)</a> |
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<li><a href="#referrers">referrers(jobject)</a> |
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<li><a href="#referees">referees(jobject)</a> |
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<li><a href="#refers">refers(jobject)</a> |
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<li><a href="#root">root(jobject)</a> |
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<li><a href="#sizeof">sizeof(jobject)</a> |
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<li><a href="#toHtml">toHtml(obj)</a> |
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</ul> |
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<a name="allocTrace"></a> |
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<h4>allocTrace function</h4> |
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This returns allocation site trace of a given Java object if available. |
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allocTrace returns array of frame objects. Each frame object has the following |
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properties: |
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<ul> |
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<li>className - name of the Java class whose method is running in the frame. |
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<li>methodName - name of the Java method running in the frame. |
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<li>methodSignature - signature of the Java method running in the frame. |
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<li>sourceFileName - name of source file of the Java class running in the frame. |
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<li>lineNumber - source line number within the method. |
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</ul> |
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<a name="classof"></a> |
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<h4>classof function</h4> |
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Returns Class object of a given Java Object. The result object supports the |
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following properties: |
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<ul> |
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<li>name - name of the class. |
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<li>superclass - Class object for super class (or null if java.lang.Object). |
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<li>statics - name, value pairs for static fields of the Class. |
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<li>fields - array of field objects. Field objects have name, signature |
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properties. |
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<li>loader - ClassLoader object that loaded this class. |
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<li>signers - signers that signed this class. |
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<li>protectionDomain - protection domain to which this class belongs. |
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</ul> |
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Class objects have the following methods: |
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<ul> |
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<li>isSubclassOf - tests whether given class is direct or indirect |
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subclass of this class or not. |
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<li>isSuperclassOf - tests whether given Class is direct or indirect |
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superclass of this class or not. |
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<li>subclasses - returns array of direct and indirect subclasses. |
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<li>superclasses - returns array of direct and indirect superclasses. |
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</ul> |
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Examples: |
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<ul> |
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<li>show class name of each Reference type object |
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<pre> |
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<code> |
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select classof(o).name from instanceof java.lang.ref.Reference o |
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</code> |
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<li>show all subclasses of java.io.InputStream |
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<pre> |
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<code> |
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select heap.findClass("java.io.InputStream").subclasses()
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</code> |
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<li>show all superclasses of java.io.BufferedInputStream |
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<pre> |
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<code> |
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select heap.findClass("java.io.BufferedInputStream").superclasses()
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</code> |
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</pre> |
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</ul> |
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<a name="forEachReferrer"></a> |
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<h4>forEachReferrer function</h4> |
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calls a callback function for each referrer of a given Java object. |
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<a name="identical"></a> |
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<h4>identical function</h4> |
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<p> |
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Returns whether two given Java objects are identical or not. |
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</p> |
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Example: |
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<pre> |
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<code> |
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select identical(heap.findClass("Foo").statics.bar, heap.findClass("AnotherClass").statics.bar)
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</code> |
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</pre> |
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<a name="objectid"></a> |
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<h4>objectid function</h4> |
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<p> |
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Returns String id of a given Java object. This id can be passed to |
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<a href="#findObject">heap.findObject</a> and may also be used to compare |
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objects for identity. |
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</p> |
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Example: |
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<pre> |
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<code> |
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select objectid(o) from java.lang.Object o |
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</code> |
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</pre> |
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<a name="reachables"></a> |
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<h4>reachables function</h4> |
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<p> |
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Returns an array of Java objects that are transitively referred from the |
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given Java object. Optionally accepts a second parameter that is comma |
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separated field names to be excluded from reachability computation. |
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Fields are written in class_name.field_name pattern. |
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</p> |
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Examples: |
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<ul> |
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<li>print all reachable objects from each Properties instance. |
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<pre> |
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<code> |
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select reachables(p) from java.util.Properties p |
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</code> |
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</pre> |
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<li>print all reachables from each java.net.URL but omit the objects reachable |
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via the fields specified. |
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<pre> |
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<code> |
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select reachables(u, 'java.net.URL.handler') from java.net.URL u |
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</code> |
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</pre> |
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</ul> |
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<a name="referrers"></a> |
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<h4>referrers function</h4> |
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<p> |
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Returns an enumeration of Java objects that hold reference to a given Java |
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object. |
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</p> |
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Examples: |
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<ul> |
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<li> print number of referrers for each java.lang.Object instance |
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<pre> |
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<code> |
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select count(referrers(o)) from java.lang.Object o |
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</code> |
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</pre> |
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<li>print referrers for each java.io.File object |
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<pre> |
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<code> |
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select referrers(f) from java.io.File f |
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</code> |
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</pre> |
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<li>print URL objects only if referred by 2 or more |
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<pre> |
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<code> |
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select u from java.net.URL u where count(referrers(u)) > 2 |
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</code> |
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</pre> |
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</ul> |
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<a name="referees"></a> |
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<h4>referees function</h4> |
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<p> |
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Returns an array of Java objects to which the given Java |
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object directly refers to. |
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</p> |
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Example: to print all static reference fields of java.io.File class |
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<pre> |
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<code> |
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select referees(<a href="#findClass">heap.findClass</a>("java.io.File"))
|
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</code> |
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</pre> |
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<a name="refers"></a> |
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<h4>refers function</h4> |
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<p> |
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Returns whether first Java object refers to second Java object or not. |
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</p> |
|
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||
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<a name="root"></a> |
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<h4>root function</h4> |
|
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<p> |
|
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If given object is a member of root set of objects, this function returns |
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a descriptive <a href="#rootobj">Root object</a> describing why it is so. |
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If given object is not a root, then this function returns null. |
|
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</p> |
|
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||
433 |
<a name="sizeof"></a> |
|
434 |
<h4>sizeof function</h4> |
|
435 |
||
436 |
Returns size of the given Java object in bytes |
|
437 |
Example: |
|
438 |
<pre> |
|
439 |
<code> |
|
440 |
select sizeof(o) from [I o |
|
441 |
</code> |
|
442 |
</pre> |
|
443 |
||
444 |
<a name="toHtml"></a> |
|
445 |
<h4>toHtml function</h4> |
|
446 |
||
447 |
Returns HTML string for the given Java object. Note that this is called |
|
448 |
automatically for objects selected by select expression. But, it may be useful |
|
449 |
to print more complex output. |
|
450 |
||
451 |
Example: print hyperlink in bold font weight |
|
452 |
<pre> |
|
453 |
<code> |
|
454 |
select "<b>" + toHtml(o) + "</b>" from java.lang.Object o |
|
455 |
</code> |
|
456 |
</pre> |
|
457 |
||
458 |
<h3>Selecting multiple values</h3> |
|
459 |
<p> |
|
460 |
Multiple values can be selected using JavaScript object literals or arrays. |
|
461 |
</p> |
|
462 |
||
463 |
Example: show name and thread for each thread object |
|
464 |
<pre> |
|
465 |
<code> |
|
466 |
select { name: t.name? t.name.toString() : "null", thread: t }
|
|
467 |
from instanceof java.lang.Thread t |
|
468 |
</code> |
|
469 |
</pre> |
|
470 |
||
471 |
<h3>array/iterator/enumeration manipulation functions</h3> |
|
472 |
||
473 |
<p> |
|
474 |
These functions accept an array/iterator/enumeration and an |
|
475 |
expression string [or a callback function] as input. These functions iterate |
|
476 |
the array/iterator/enumeration and apply the expression (or function) on |
|
477 |
each element. Note that JavaScript objects are associative arrays. So, |
|
478 |
these functions may also be used with arbitrary JavaScript objects. |
|
479 |
</p> |
|
480 |
||
481 |
<ul> |
|
482 |
<li><a href="#concat">concat(array1/enumeration1, array2/enumeration2)</a> |
|
483 |
<li><a href="#contains">contains(array/enumeration, expression)</a> |
|
484 |
<li><a href="#count">count(array/enumeration, expression)</a> |
|
485 |
<li><a href="#filter">filter(array/enumeration, expression)</a> |
|
486 |
<li><a href="#length">length(array/enumeration)</a> |
|
487 |
<li><a href="#map">map(array/enumeration, expression)</a> |
|
488 |
<li><a href="#max">max(array/enumeration, [expression])</a> |
|
489 |
<li><a href="#min">min(array/enumeration, [expression])</a> |
|
490 |
<li><a href="#sort">sort(array/enumeration, [expression])</a> |
|
491 |
<li><a href="#sum">sum(array/enumeration, [expression])</a> |
|
492 |
<li><a href="#toArray">toArray(array/enumeration)</a> |
|
493 |
<li><a href="#unique">unique(array/enumeration, [expression])</a> |
|
494 |
</ul> |
|
495 |
||
496 |
<a name="concat"></a> |
|
497 |
<h4>concat function</h4> |
|
498 |
<p> |
|
499 |
Concatenates two arrays or enumerations (i.e., returns composite |
|
500 |
enumeration). |
|
501 |
</p> |
|
502 |
||
503 |
<a name="contains"></a> |
|
504 |
<h4>contains function</h4> |
|
505 |
<p> |
|
506 |
Returns whether the given array/enumeration contains an element |
|
507 |
the given boolean expression specified in code. The code evaluated |
|
508 |
can refer to the following built-in variables. |
|
509 |
</p> |
|
510 |
<ul> |
|
511 |
<li>it -> currently visited element |
|
512 |
<li>index -> index of the current element |
|
513 |
<li>array -> array/enumeration that is being iterated |
|
514 |
</ul> |
|
515 |
Example: select all Properties objects that are referred by |
|
516 |
some static field some class. |
|
517 |
<pre> |
|
518 |
<code> |
|
519 |
select p from java.util.Properties p |
|
520 |
where contains(<a href="#referrers">referrers</a>(p), "<a href="#classof">classof</a>(it).name == 'java.lang.Class'") |
|
521 |
</code> |
|
522 |
</pre> |
|
523 |
||
524 |
<a name="count"></a> |
|
525 |
<h4>count function</h4> |
|
526 |
<p> |
|
527 |
count function returns the count of elements of the input array/enumeration |
|
528 |
that satisfy the given boolean expression. The boolean expression code can |
|
529 |
refer to the following built-in variables. |
|
530 |
</p> |
|
531 |
<ul> |
|
532 |
<li>it -> currently visited element |
|
533 |
<li>index -> index of the current element |
|
534 |
<li>array -> array/enumeration that is being iterated |
|
535 |
</ul> |
|
536 |
Example: print number of classes that have specific name pattern |
|
537 |
<pre> |
|
538 |
<code> |
|
539 |
select count(<a href="#classes">heap.classes()</a>, "/java.io./(it.name)") |
|
540 |
</code> |
|
541 |
</pre> |
|
542 |
||
543 |
<a name="filter"></a> |
|
544 |
<h4>filter function</h4> |
|
545 |
<p> |
|
546 |
filter function returns an array/enumeration that contains elements |
|
547 |
of the input array/enumeration that satisfy the given boolean |
|
548 |
expression. The boolean expression code can refer to the following built-in |
|
549 |
variables. |
|
550 |
</p> |
|
551 |
<ul> |
|
552 |
<li>it -> currently visited element |
|
553 |
<li>index -> index of the current element |
|
554 |
<li>array -> array/enumeration that is being iterated |
|
555 |
<li>result -> result array/enumeration |
|
556 |
</ul> |
|
557 |
Examples: |
|
558 |
<ul> |
|
559 |
<li>show all classes that have java.io.* name pattern |
|
560 |
<pre> |
|
561 |
<code> |
|
562 |
select filter(<a href="#classes">heap.classes</a>(), "/java.io./(it.name)") |
|
563 |
</code> |
|
564 |
</pre> |
|
565 |
<li> show all referrers of URL object where the referrer is not from |
|
566 |
java.net package |
|
567 |
<pre> |
|
568 |
<code> |
|
569 |
select filter(<a href="#referrers">referrers</a>(u), "! /java.net./(<a href="#classof">classof</a>(it).name)") |
|
570 |
from java.net.URL u |
|
571 |
</code> |
|
572 |
</pre> |
|
573 |
</ul> |
|
574 |
||
575 |
<a name="length"></a> |
|
576 |
<h4>length function</h4> |
|
577 |
<p> |
|
578 |
length function returns number of elements of an array/enumeration. |
|
579 |
</p> |
|
580 |
||
581 |
<a name="map"></a> |
|
582 |
<h4>map function</h4> |
|
583 |
<p> |
|
584 |
Transforms the given array/enumeration by evaluating given code |
|
585 |
on each element. The code evaluated can refer to the following built-in |
|
586 |
variables. |
|
587 |
</p> |
|
588 |
<ul> |
|
589 |
<li>it -> currently visited element |
|
590 |
<li>index -> index of the current element |
|
591 |
<li>array -> array/enumeration that is being iterated |
|
592 |
<li>result -> result array/enumeration |
|
593 |
</ul> |
|
594 |
<p> |
|
595 |
map function returns an array/enumeration of values created by repeatedly |
|
596 |
calling code on each element of input array/enumeration. |
|
597 |
</p> |
|
598 |
Example: show all static fields of java.io.File with name and value |
|
599 |
<pre> |
|
600 |
<code> |
|
601 |
select map(<a href="#findClass">heap.findClass</a>("java.io.File").statics, "index + '=' + <a href="#toHtml">toHtml</a>(it)")
|
|
602 |
</code> |
|
603 |
</pre> |
|
604 |
||
605 |
<a name="max"></a> |
|
606 |
<h4>max function</h4> |
|
607 |
<p> |
|
608 |
returns the maximum element of the given array/enumeration. |
|
609 |
Optionally accepts code expression to compare elements of the array. |
|
610 |
By default numerical comparison is used. The comparison expression can |
|
611 |
use the following built-in variables: |
|
612 |
</p> |
|
613 |
<ul> |
|
614 |
<li>lhs -> left side element for comparison |
|
615 |
<li>rhs -> right side element for comparison |
|
616 |
</ul> |
|
617 |
Examples: |
|
618 |
<ul> |
|
619 |
<li>find the maximum length of any String instance |
|
620 |
<pre> |
|
621 |
<code> |
|
622 |
select max(map(heap.objects('java.lang.String', false), 'it.count'))
|
|
623 |
</code> |
|
624 |
</pre> |
|
625 |
<li>find string instance that has the maximum length |
|
626 |
<pre> |
|
627 |
<code> |
|
628 |
select max(heap.objects('java.lang.String'), 'lhs.count > rhs.count')
|
|
629 |
</code> |
|
630 |
</pre> |
|
631 |
</ul> |
|
632 |
||
633 |
<a name="min"></a> |
|
634 |
<h4>min function</h4> |
|
635 |
<p> |
|
636 |
returns the minimum element of the given array/enumeration. Optionally |
|
637 |
accepts code expression to compare elements of the array. By default numerical |
|
638 |
comparison is used. The comparison expression can use the following built-in |
|
639 |
variables: |
|
640 |
</p> |
|
641 |
<ul> |
|
642 |
<li>lhs -> left side element for comparison |
|
643 |
<li>rhs -> right side element for comparison |
|
644 |
</ul> |
|
645 |
Examples: |
|
646 |
<ul> |
|
647 |
<li>find the minimum size of any Vector instance |
|
648 |
<pre> |
|
649 |
<code> |
|
650 |
select min(map(heap.objects('java.util.Vector', false), 'it.elementData.length'))
|
|
651 |
</code> |
|
652 |
</pre> |
|
653 |
<li>find Vector instance that has the maximum length |
|
654 |
<pre> |
|
655 |
<code> |
|
656 |
select min(heap.objects('java.util.Vector'), 'lhs.elementData.length < rhs.elementData.length')
|
|
657 |
</code> |
|
658 |
</ul> |
|
659 |
||
660 |
<a name="sort"></a> |
|
661 |
<h4>sort function</h4> |
|
662 |
<p> |
|
663 |
sorts given array/enumeration. Optionally accepts code expression to |
|
664 |
compare elements of the array. By default numerical comparison is used. |
|
665 |
The comparison expression can use the following built-in variables: |
|
666 |
</p> |
|
667 |
<ul> |
|
668 |
<li>lhs -> left side element for comparison |
|
669 |
<li>rhs -> right side element for comparison |
|
670 |
</ul> |
|
671 |
Examples: |
|
672 |
<ul> |
|
673 |
<li> print all char[] objects in the order of size. |
|
674 |
<pre> |
|
675 |
<code> |
|
676 |
select sort(<a href="#objects">heap.objects</a>('[C'), '<a href="#sizeof">sizeof</a>(lhs) - sizeof(rhs)')
|
|
677 |
</code> |
|
678 |
</pre> |
|
679 |
<li> print all char[] objects in the order of size but print |
|
680 |
size as well. |
|
681 |
<pre> |
|
682 |
<code> |
|
683 |
select <a href="#map">map</a>(sort(<a href="#objects">heap.objects</a>('[C'), '<a href="#sizeof">sizeof</a>(lhs) - sizeof(rhs)'), '{ size: sizeof(it), obj: it }')
|
|
684 |
</code> |
|
685 |
</pre> |
|
686 |
</ul> |
|
687 |
||
688 |
<a name="sum"></a> |
|
689 |
<h4>sum function</h4> |
|
690 |
<p> |
|
691 |
This function returns the sum of all the elements of the given input array or |
|
692 |
enumeration. Optionally, accepts an expression as second param. This is used |
|
693 |
to map the input elements before summing those. |
|
694 |
</p> |
|
695 |
Example: return sum of sizes of the reachable objects from each Properties object |
|
696 |
<pre> |
|
697 |
<code> |
|
698 |
select sum(<a href="#map">map</a>(<a href="#reachables">reachables</a>(p), '<a href="#sizeof">sizeof</a>(it)')) |
|
699 |
from java.util.Properties p |
|
700 |
||
701 |
// or omit the map as in ... |
|
702 |
select sum(<a href="#reachables">reachables</a>(p), '<a href="#sizeof">sizeof</a>(it)') |
|
703 |
from java.util.Properties p |
|
704 |
</code> |
|
705 |
</code> |
|
706 |
</pre> |
|
707 |
||
708 |
<a name="toArray"></a> |
|
709 |
<h4>toArray function</h4> |
|
710 |
<p> |
|
711 |
This function returns an array that contains elements of the input |
|
712 |
array/enumeration. |
|
713 |
</p> |
|
714 |
||
715 |
<a name="unique"></a> |
|
716 |
<h4>unique function</h4> |
|
717 |
<p> |
|
718 |
This function returns an array/enumeration containing unique elements of the |
|
719 |
given input array/enumeration |
|
720 |
</p> |
|
721 |
Example: select unique char[] instances referenced from Strings. Note that |
|
722 |
more than one String instance can share the same char[] for the content. |
|
723 |
<pre> |
|
724 |
<code> |
|
725 |
// number of unique char[] instances referenced from any String |
|
726 |
select count(unique(map(heap.objects('java.lang.String'), 'it.value')))
|
|
727 |
||
728 |
// total number of Strings |
|
729 |
select count(heap.objects('java.lang.String'))
|
|
730 |
</code> |
|
731 |
</pre> |
|
732 |
||
733 |
<h3>More complex examples</h3> |
|
734 |
||
735 |
<h4>Print histogram of each class loader and number of classes loaded by it</h4> |
|
736 |
||
737 |
<pre> |
|
738 |
<code> |
|
739 |
select <a href="#map">map</a>(<a href="#sort">sort</a>(map(heap.objects('java.lang.ClassLoader'),
|
|
740 |
'{ loader: it, count: it.classes.elementCount }'), 'lhs.count < rhs.count'),
|
|
741 |
'toHtml(it) + "<br>"') |
|
742 |
</code> |
|
743 |
</pre> |
|
744 |
<p> |
|
745 |
The above query uses the fact that, <b>java.lang.ClassLoader</b> has a private |
|
746 |
field called <b>classes</b> of type <b>java.util.Vector</b> and Vector has a |
|
747 |
private field named <b>elementCount</b> that is number of elements in the |
|
748 |
vector. We select multiple values (loader, count) using JavaScript object |
|
749 |
literal and map function. We sort the result by count (i.e., number of classes |
|
750 |
loaded) using sort function with comparison expression. |
|
751 |
</p> |
|
752 |
||
753 |
<h4>Show parent-child chain for each class loader instance</h4> |
|
754 |
||
755 |
<pre> |
|
756 |
<code> |
|
757 |
select <a href="#map">map</a>(heap.objects('java.lang.ClassLoader'),
|
|
758 |
function (it) {
|
|
759 |
var res = ''; |
|
760 |
while (it != null) {
|
|
761 |
res += toHtml(it) + "->"; |
|
762 |
it = it.parent; |
|
763 |
} |
|
764 |
res += "null"; |
|
765 |
return res + "<br>"; |
|
766 |
}) |
|
767 |
</code> |
|
768 |
</pre> |
|
769 |
<p> |
|
770 |
Note that we use <b>parent</b> field of <b>java.lang.ClassLoader</b> class |
|
771 |
and walk until parent is null using the callback function to map call. |
|
772 |
</p> |
|
773 |
||
774 |
<h4>Printing value of all System properties</h4> |
|
775 |
||
776 |
<pre> |
|
777 |
<code> |
|
778 |
select <a href="#map">map</a>(<a href="#filter">filter(<a href="#findClass">heap.findClass</a>('java.lang.System').props.table, 'it != null'),
|
|
779 |
function (it) {
|
|
780 |
var res = ""; |
|
781 |
while (it != null) {
|
|
782 |
res += it.key.value.toString() + '=' + |
|
783 |
it.value.value.toString() + '<br>'; |
|
784 |
it = it.next; |
|
785 |
} |
|
786 |
return res; |
|
787 |
}); |
|
788 |
</code> |
|
789 |
</pre> |
|
790 |
<p> |
|
791 |
The above query uses the following facts: |
|
792 |
<ul> |
|
793 |
<li>java.lang.System has static field by name 'props' of type java.util.Properties. |
|
794 |
<li>java.util.Properties has field by 'table' of type java.util.Hashtable$Entry |
|
795 |
(this field is inherited from java.util.Hashtable). This is the hashtable |
|
796 |
buckets array. |
|
797 |
<li>java.util.Hashtable$Entry has 'key', 'value' and 'next' fields. Each |
|
798 |
entry points the next entry (or null) in the same hashtable bucket. |
|
799 |
<li>java.lang.String class has 'value' field of type char[]. |
|
800 |
</ul> |
|
801 |
<p> |
|
802 |
<b>Note that this query (and many other queries) may not be stable - because |
|
803 |
private fields of Java platform classes may be modified/removed without any |
|
804 |
notification! (implementation detail)</b>. But, using such queries on user |
|
805 |
classes may be safe - given that user has the control over the classes. |
|
806 |
</p> |
|
807 |
||
808 |
</body> |
|
809 |
</html> |