Question

I currently have this code:

private void compile(){ 

        List<File> files = getListOfJavaFiles();

        //JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
        //compiler.run(null, null, null, srcDirectory.getPath()+"/Main.java");

        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
           StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null);

           Iterable<? extends JavaFileObject> compilationUnits1 =
               fileManager.getJavaFileObjectsFromFiles(files);

           List<String> optionList = new ArrayList<String>();
           // set compiler's classpath to be same as the runtime's
           optionList.addAll(Arrays.asList("-classpath",System.getProperty("java.class.path")));

           //need to add options here.
           compiler.getTask(null, fileManager, null, optionList, null, compilationUnits1).call();

           //compiler.run(null, null, null, srcDirectory.getPath()+"/Main.java");
          // fileManager.close();

    }

But I am stuck now trying to make this actually run the files which have been compiled.
I see no output from this in the console, however in the Main.java file which I have compiled successfully (I can see the .class files), I have put “System.out.println(“Main class is running”);, so I would expect to see this when I run the application.

Answer 1

You can create an URLClassLoader to load your newly compiled classes, or you can have a look at a library I wrote which will compile in memory and load into the current class loader by default.

http://vanillajava.blogspot.co.uk/2010/11/more-uses-for-dynamic-code-in-java.html

If you have generated code, it will save the file to a source directory when debugging so you can step into the generated code (otherwise it does everything in memory)

You can only load a class once this way so if you need to load many versions I suggest you implement an interface and change the name of the class each time.

// this writes the file to disk only when debugging is enabled.
CachedCompiler cc = CompilerUtils.DEBUGGING ?
        new CachedCompiler(new File(parent, "src/test/java"), new File(parent, "target/compiled")) :
        CompilerUtils.CACHED_COMPILER;

String text = "generated test " + new Date();
Class fooBarTeeClass = cc.loadFromJava("eg.FooBarTee", "package eg;\n" +
    '\n' +
    "import eg.components.BarImpl;\n" +
    "import eg.components.TeeImpl;\n" +
    "import eg.components.Foo;\n" +
    '\n' +
    "public class FooBarTee{\n" +
    "    public final String name;\n" +
    "    public final TeeImpl tee;\n" +
    "    public final BarImpl bar;\n" +
    "    public final BarImpl copy;\n" +
    "    public final Foo foo;\n" +
    '\n' +
    "    public FooBarTee(String name) {\n" +
    "        // when viewing this file, ensure it is synchronised with the copy on disk.\n" +
    "        System.out.println(\"" + text + "\");\n" +
    "        this.name = name;\n" +
    '\n' +
    "        tee = new TeeImpl(\"test\");\n" +
    '\n' +
    "        bar = new BarImpl(tee, 55);\n" +
    '\n' +
    "        copy = new BarImpl(tee, 555);\n" +
    '\n' +
    "        // you should see the current date here after synchronisation.\n" +
    "        foo = new Foo(bar, copy, \"" + text + "\", 5);\n" +
    "    }\n" +
    '\n' +
    "    public void start() {\n" +
    "    }\n" +
    '\n' +
    "    public void stop() {\n" +
    "    }\n" +
    '\n' +
    "    public void close() {\n" +
    "        stop();\n" +
    '\n' +
    "    }\n" +
    "}\n");

// add a debug break point here and step into this method.
FooBarTee fooBarTee = new FooBarTee("test foo bar tee");
Foo foo = fooBarTee.foo;
assertNotNull(foo);
assertEquals(text, foo.s);