Java Compiler API - JavaFileManager, DiagnosticListener and DiagnosticCollector Examples

public class FileManagerExample {
    public static void main(String[] args) throws ExecutionException, InterruptedException, IOException {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        //Already available DiagnosticListener implementation
        DiagnosticCollector<JavaFileObject> diagnostics =
                new DiagnosticCollector<>();

        //that's how we get the instance of StandardJavaFileManager
        //the compiler just returns the new instance.
        StandardJavaFileManager standardFileManager =
                compiler.getStandardFileManager(diagnostics, null, null);

        File file = new File("test-sources/FileWithErrors.java");

        //files are wrapped into JavaFileObjects by StandardFileManager
        Iterable<? extends JavaFileObject> javaFileObjects =
                standardFileManager.getJavaFileObjects(file);
        for (JavaFileObject javaFileObject : javaFileObjects) {
            System.out.println(javaFileObject.getClass());
        }


        //we still have to pass file manager and others as compiler doesn't track
        //anything about them. Also there might be a new instance of customized
        //StandardFileManager here.
        JavaCompiler.CompilationTask task = compiler.getTask(
                null, standardFileManager, diagnostics, null,
                null, javaFileObjects);

        Future<Boolean> future = Executors.newFixedThreadPool(1).submit(task);
        Boolean result = future.get();
        if (result != null && result) {
            System.out.println("Compilation done");
        } else {
            // we might show the diagnostics other than
            // standard output e.g. in some GUI screen.
            diagnostics.getDiagnostics().forEach(System.out::println);
        }
        standardFileManager.close();
    }
}

import javax.tools.*;
import java.io.IOException;
import java.util.Arrays;

public class StringCompilation {

    public static void main(String[] args) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        DiagnosticCollector<JavaFileObject> diagnostics =
                new DiagnosticCollector<>();

        String className = "Test";

        final JavaByteObject byteObject = new JavaByteObject(className);

        StandardJavaFileManager standardFileManager =
                compiler.getStandardFileManager(diagnostics, null, null);

        JavaFileManager fileManager = createFileManager(standardFileManager,
                                                                 byteObject);

        JavaCompiler.CompilationTask task = compiler.getTask(null,
                fileManager, diagnostics, null, null, getCompilationUnits(className));

        if (!task.call()) {
            diagnostics.getDiagnostics().forEach(System.out::println);
        }
        fileManager.close();

        //loading and using our compiled class
        final ClassLoader inMemoryClassLoader = createClassLoader(byteObject);
        Class<ITest> test = (Class<ITest>) inMemoryClassLoader.loadClass(className);
        ITest iTest = test.newInstance();
        iTest.doSomething();
    }

    private static JavaFileManager createFileManager(StandardJavaFileManager fileManager,
                                                     JavaByteObject byteObject) {
        return new ForwardingJavaFileManager<StandardJavaFileManager>(fileManager) {
            @Override
            public JavaFileObject getJavaFileForOutput(Location location,
                                                       String className, JavaFileObject.Kind kind,
                                                       FileObject sibling) throws IOException {
                return byteObject;
            }
        };
    }

    private static ClassLoader createClassLoader(final JavaByteObject byteObject) {
        return new ClassLoader() {
            @Override
            public Class<?> findClass(String name) throws ClassNotFoundException {
                //no need to search class path, we already have byte code.
                byte[] bytes = byteObject.getBytes();
                return defineClass(name, bytes, 0, bytes.length);
            }
        };
    }

    public static Iterable<? extends JavaFileObject> getCompilationUnits(String className) {
        JavaStringObject stringObject =
                new JavaStringObject(className, getSource());
        return Arrays.asList(stringObject);
    }

    public static String getSource() {
        return "public class Test implements com.logicbig.example.ITest{" +
                "public void doSomething(){" +
                "System.out.println(\"testing\");}}";
    }
}

public class StringCompilation {

    private static final File outputFile;

    static {
        String outputPath = System.getProperty("user.dir") +
                File.separatorChar + "compiledClasses";
        outputFile = new File(outputPath);
        if (!outputFile.exists()) {
            try {
                Files.createDirectory(outputFile.toPath());
            } catch (IOException e) {
                throw new RuntimeException(e);
            }
        }
    }

    public static void main(String[] args) throws Exception {
        JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();

        DiagnosticCollector<JavaFileObject> diagnostics =
                new DiagnosticCollector<>();

        StandardJavaFileManager fileManager =
                compiler.getStandardFileManager(diagnostics, null, null);


        fileManager.setLocation(StandardLocation.CLASS_OUTPUT,
                Arrays.asList(outputFile));

        JavaCompiler.CompilationTask task = compiler.getTask(null,
                fileManager, diagnostics, null, null, getCompilationUnits());

        if (!task.call()) {
            diagnostics.getDiagnostics().forEach(System.out::println);
        }
        fileManager.close();

        //loading and using our compiled class
        ClassLoader loader = new URLClassLoader(new URL[]{outputFile.toURI().toURL()});
        Class<ITest> test = (Class<ITest>) loader.loadClass("Test");
        ITest iTest = test.newInstance();
        iTest.doSomething();
    }

    public static Iterable<? extends JavaFileObject> getCompilationUnits() {
        JavaStringObject stringObject =
                new JavaStringObject("Test", getSource());
        return Arrays.asList(stringObject);
    }

    public static String getSource() {
        return "public class Test implements com.logicbig.example.ITest{" +
                "public void doSomething(){" +
                "System.out.println(\"testing\");}}";
    }
}