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See the License for the specific language governing permissions and limitations under the License. --> <html lang="en"> <head> <link rel="stylesheet" type="text/css" href="../stylesheets/style.css"> <title>Javah Task</title> </head> <body> <h2 id="javah">Javah</h2> <h3>Description</h3> <p>Generates JNI headers from a Java class.</p> <p>When this task executes, it will generate the C header and source files that are needed to implement native methods. JNI operates differently depending on whether <a href="https://docs.oracle.com/javase/8/docs/technotes/tools/windows/javah.html" target="_top">JDK 1.2+</a> or <a href="https://web.archive.org/web/20021018232717/http://java.sun.com/products/jdk/1.1/docs/tooldocs/win32/javah.html" target="_top">pre-1.2 JDK</a> systems are used.</p> <p>If you are building with Java 8 or above consider using <a href="javac.html"><code>javac</code></a>'s <var>nativeheaderdir</var> attribute instead which allows you to compile the classes and generate the native header files in a single step.</p> <p><strong>Note</strong>: <code>javah</code> has been deprecated in Java 9 and removed in Java 10. Attempts to use it with Java 10 will fail.</p> <p id="implementationvalues">It is possible to use different compilers. This can be selected with the <var>implementation</var> attribute or a nested element. Here are the choices of the attribute:</p> <ul> <li><q>default</q>—the default compiler for the platform.</li> <li><q>sun</q>—the standard compiler of the JDK.</li> <li><q>kaffeh</q>—the native standard compiler of <a href="https://github.com/kaffe/kaffe" target="_top">Kaffe</a>.</li> <li><q>gcjh</q>—the native standard compiler of <a href="https://gcc.gnu.org/gcc-7/changes.html#java" target="_top">gcj and gij</a>. <em>Since Apache Ant 1.8.2</em></li> <li><q>forking</q>—runs the <kbd>javah</kbd> executable via its command line interface in a separate process. Default when not running on Kaffe or gcj/gij <em>since Ant 1.9.8</em></li> </ul> <p><strong>Note</strong>: if you are using this task to work on multiple files the command line may become too long on some operating systems. Unfortunately the <kbd>javah</kbd> command doesn't support command argument files the way <kbd>javac</kbd> (for example) does, so all that can be done is breaking the amount of classes to compile into smaller chunks.</p> <h3>Parameters</h3> <table class="attr"> <tr> <th scope="col">Attribute</th> <th scope="col">Description</th> <th scope="col">Required</th> </tr> <tr> <td>class</td> <td>the fully-qualified name of the class (or classes, separated by commas)</td> <td>Yes</td> </tr> <tr> <td>outputFile</td> <td>concatenates the resulting header or source files for all the classes listed into this file</td> <td rowspan="2">Exactly one of the two</td> </tr> <tr> <td>destdir</td> <td class="left">sets the directory where <kbd>javah</kbd> saves the header files or the stub files.</td> </tr> <tr> <td>force</td> <td>specifies that output files should always be written (JDK 1.2 only)</td> <td>No</td> </tr> <tr> <td>old</td> <td>specifies that old JDK 1.0-style header files should be generated (otherwise output file contain JNI-style native method function prototypes) (JDK 1.2 only)</td> <td>No</td> </tr> <tr> <td>stubs</td> <td>generate C declarations from the Java object file (used with <var>old</var>)</td> <td>No</td> </tr> <tr> <td>verbose</td> <td>causes <kbd>javah</kbd> to print a message concerning the status of the generated files</td> <td>No</td> </tr> <tr> <td>classpath</td> <td>the classpath to use</td> <td>No</td> </tr> <tr> <td>bootclasspath</td> <td>location of bootstrap class files</td> <td>No</td> </tr> <tr> <td>extdirs</td> <td>location of installed extensions</td> <td>No</td> </tr> <tr> <td>implementation</td> <td>The compiler implementation to use. (See the above <a href="#implementationvalues">list</a> of valid compilers.)</td> <td>No; defaults to default compiler for the current JDK</td> </tr> </table> <h3>Parameters specified as nested elements</h3> <h4>arg</h4> <p>You can specify additional command line arguments for the compiler with nested <code><arg></code> elements. These elements are specified like <a href="../using.html#arg">Command-line Arguments</a> but have an additional attribute that can be used to enable arguments only if a given compiler implementation will be used.</p> <table class="attr"> <tr> <th scope="col">Attribute</th> <th scope="col">Description</th> <th scope="col">Required</th> </tr> <tr> <td>value</td> <td rowspan="4">See <a href="../using.html#arg">Command-line Arguments</a>.</td> <td rowspan="4">Exactly one of these</td> </tr> <tr> <td class="var">line</td> </tr> <tr> <td class="var">file</td> </tr> <tr> <td class="var">path</td> </tr> <tr> <td>prefix</td> <td rowspan="2">See <a href="../using.html#arg">Command-line Arguments</a>. <em>Since Ant 1.8</em>.</td> <td>No</td> </tr> <tr> <td>suffix</td> <td>No</td> </tr> <tr> <td>implementation</td> <td>Only pass the specified argument if the chosen compiler implementation matches the value of this attribute. Legal values are the same as those in the above <a href="#implementationvalues">list</a> of valid compilers.)</td> <td>No</td> </tr> </table> <h4>implementationclasspath</h4> <p><em>Since Ant 1.8.0</em></p> <p>A <a href="../using.html#path">path-like structure</a> holding the classpath to use when loading the compiler implementation if a custom class has been specified. Doesn't have any effect when using one of the built-in compilers.</p> <h4>Any nested element of a type that implements JavahAdapter</h4> <p><em>Since Ant 1.8.0</em></p> <p>If a defined type implements the <code class="code">JavahAdapter</code> interface a nested element of that type can be used as an alternative to the <var>implementation</var> attribute.</p> <h3>Examples</h3> <p>Make a JNI header of the named class, using the JDK 1.2 JNI model. Assuming the directory <samp>c</samp> already exists, the file <samp>org_foo_bar_Wibble.h</samp> is created there. If this file already exists, it is left unchanged.</p> <pre><javah destdir="c" class="org.foo.bar.Wibble"/></pre> <p>This is similar to the previous example, except the output is written to a file called <samp>wibble.h</samp> in the current directory.</p> <pre> <javah outputFile="wibble.h"> <class name="org.foo.bar.Wibble,org.foo.bar.Bobble"/> </javah></pre> <p>Write three header files, one for each of the classes named. Because the <var>force</var> option is set, these header files are always written when the <code>Javah</code> task is invoked, even if they already exist.</p> <pre> <javah destdir="c" force="yes"> <class name="org.foo.bar.Wibble"/> <class name="org.foo.bar.Bobble"/> <class name="org.foo.bar.Tribble"/> </javah></pre> <p>Write the headers for the three classes using the 'old' JNI format, then write the corresponding <samp>.c</samp> stubs. The <var>verbose</var> option will cause <code>Javah</code> to describe its progress.</p> <pre> <javah destdir="c" verbose="yes" old="yes" force="yes"> <class name="org.foo.bar.Wibble"/> <class name="org.foo.bar.Bobble"/> <class name="org.foo.bar.Tribble"/> </javah> <javah destdir="c" verbose="yes" stubs="yes" old="yes" force="yes"> <class name="org.foo.bar.Wibble"/> <class name="org.foo.bar.Bobble"/> <class name="org.foo.bar.Tribble"/> </javah></pre> <p>If you want to use a custom <code class="code">JavahAdapter</code> <code>org.example.MyAdapter</code> you can either use the <var>implementation</var> attribute:</p> <pre> <javah destdir="c" class="org.foo.bar.Wibble" implementation="org.example.MyAdapter"/></pre> <p>or a define a type and nest this into the task like in:</p> <pre> <componentdef classname="org.example.MyAdapter" name="myadapter"/> <javah destdir="c" class="org.foo.bar.Wibble"> <myadapter/> </javah></pre> <p>in which case your <code>javah</code> adapter can support attributes and nested elements of its own.</p> </body> </html>