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POCompile java files programmatically
 

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    <p>I know this has been asked and answered a lot but I still don't have a good solution and I still don't understand some parts. So I have the requirement to compile *.java files programmatically.</p> <pre><code>JavaCompiler compiler = ToolProvider.getSystemJavaCompiler(); </code></pre> <p>is what I'm using and (as expected) the compiler is <code>null</code>. Now, I do know that I have to use the JDK and not the JRE as a "runtime", but here is something I don't understand: isn't it enough to just put <code>tools.jar</code> in the classpath of the application and then have access to the Java Compiler API? If this is true, is there (I think there is) difference between a stand-alone java application and web-based application. Actually, I am trying to summon the JavaCompiler from a PlayFramework webapp so I figured out, maybe this solutions (with including the <code>tools.jar</code>) only works for stand-alone applications?</p> <p>I also tried to create a custom ClassLoader and invoke the above mentioned method with reflection but all I am getting is <code>null</code> for the <code>compiler</code> object:</p> <pre><code>ClassLoader classloader = app.classloader(); File file = new File("lib/tools.jar"); URL url = file.toURI().toURL(); URL[] urls = new URL[]{url}; ClassLoader newCL = new URLClassLoader(urls, classloader) { }; Class&lt;?&gt; loadClass = newCL.loadClass("javax.tools.ToolProvider"); Method method = loadClass.getMethod("getSystemJavaCompiler", null); Object object = method.invoke(null); System.out.println("Object: " + object); // NULL </code></pre> <p>Explanation for the code above:</p> <ul> <li>I haven't included try/catches for the sake of simplicity.</li> <li>app.classloader() is a Play-method which returns the ClassLoader of the App</li> <li><code>tools.jar</code> is included in my lib folder of the Play project (this implies that it is on the project's classpath - according to the Play documentation)</li> </ul> <p>I am pretty sure there is something else I need to do before Play is able to load the Java Compiler class I just don't know what I am missing.</p> <p>Options like <code>Runtime.exec("javac myFile.java")</code> and the Eclipse JDT compiler are known to me, but that's not what I am looking for.</p> <p>Oh, and something like <code>System.setProperty("java.home", "PATH_TO_YOUR_JDK");</code> and then <code>ToolProvider.getSystemJavaCompiler();</code> is working but I find this solution so ugly.</p> <p>Best regards</p> <p><strong>EDIT</strong>: (to give additional information and reflect the last status) This is a basic representation of web-app-structure:</p> <pre><code>myApp |-conf\... |-lib\MyJar.jar |-lib\tools.jar |-logs\... |-... </code></pre> <p>MyJar.jar has now a <code>META-INF/MANIFEST.MF</code> file with the following content:</p> <pre><code>Manifest-Version: 1.0 Sealed: true Main-Class: here.comes.my.main.class Class-Path: tools.jar </code></pre> <p><em>Without</em> starting the Play app, I am trying (in the <code>lib</code> folder): <code>java -jar MyJar.jar</code> - my simple <code>main</code> method tries to invoke the Compiler (<code>ToolProvider.getSystemJavaCompiler();</code>) and returns <code>null</code>. So this leads me to believe, that the problem has nothing to do with Play - I can't even get a Compiler when normally running my Jar!</p>
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