Examples with GeneratorAdapter act.asm.commons.GeneratorAdapter used on opensource projects

Example 1 with GeneratorAdapter

use of act.asm.commons.GeneratorAdapter in project actframework by actframework.

the class HelloWorld method main.

public static void main(final String[] args) throws Exception {
    // Generates the bytecode corresponding to the following Java class:
    // 
    // public class Example {
    // public static void main (String[] args) {
    // System.out.println("Hello world!");
    // }
    // }
    // creates a ClassWriter for the Example public class,
    // which inherits from Object
    ClassWriter cw = new ClassWriter(0);
    cw.visit(V1_1, ACC_PUBLIC, "Example", null, "java/lang/Object", null);
    // creates a MethodWriter for the (implicit) constructor
    MethodVisitor mw = cw.visitMethod(ACC_PUBLIC, "<init>", "()V", null, null);
    // pushes the 'this' variable
    mw.visitVarInsn(ALOAD, 0);
    // invokes the super class constructor
    mw.visitMethodInsn(INVOKESPECIAL, "java/lang/Object", "<init>", "()V", false);
    mw.visitInsn(RETURN);
    // this code uses a maximum of one stack element and one local variable
    mw.visitMaxs(1, 1);
    mw.visitEnd();
    // creates a MethodWriter for the 'main' method
    mw = cw.visitMethod(ACC_PUBLIC + ACC_STATIC, "main", "([Ljava/lang/String;)V", null, null);
    // pushes the 'out' field (of type PrintStream) of the System class
    mw.visitFieldInsn(GETSTATIC, "java/lang/System", "out", "Ljava/io/PrintStream;");
    // pushes the "Hello World!" String constant
    mw.visitLdcInsn("Hello world!");
    // invokes the 'println' method (defined in the PrintStream class)
    mw.visitMethodInsn(INVOKEVIRTUAL, "java/io/PrintStream", "println", "(Ljava/lang/String;)V", false);
    mw.visitInsn(RETURN);
    // this code uses a maximum of two stack elements and two local
    // variables
    mw.visitMaxs(2, 2);
    mw.visitEnd();
    // gets the bytecode of the Example class, and loads it dynamically
    byte[] code = cw.toByteArray();
    FileOutputStream fos = new FileOutputStream("Example.class");
    fos.write(code);
    fos.close();
    HelloWorld loader = new HelloWorld();
    Class<?> exampleClass = loader.defineClass("Example", code, 0, code.length);
    // uses the dynamically generated class to print 'HelloWorld'
    exampleClass.getMethods()[0].invoke(null, new Object[] { null });
    // ------------------------------------------------------------------------
    // Same example with a GeneratorAdapter (more convenient but slower)
    // ------------------------------------------------------------------------
    cw = new ClassWriter(ClassWriter.COMPUTE_MAXS);
    cw.visit(V1_1, ACC_PUBLIC, "Example", null, "java/lang/Object", null);
    // creates a GeneratorAdapter for the (implicit) constructor
    Method m = Method.getMethod("void <init> ()");
    GeneratorAdapter mg = new GeneratorAdapter(ACC_PUBLIC, m, null, null, cw);
    mg.loadThis();
    mg.invokeConstructor(Type.getType(Object.class), m);
    mg.returnValue();
    mg.endMethod();
    // creates a GeneratorAdapter for the 'main' method
    m = Method.getMethod("void main (String[])");
    mg = new GeneratorAdapter(ACC_PUBLIC + ACC_STATIC, m, null, null, cw);
    mg.getStatic(Type.getType(System.class), "out", Type.getType(PrintStream.class));
    mg.push("Hello world!");
    mg.invokeVirtual(Type.getType(PrintStream.class), Method.getMethod("void println (String)"));
    mg.returnValue();
    mg.endMethod();
    cw.visitEnd();
    code = cw.toByteArray();
    loader = new HelloWorld();
    exampleClass = loader.defineClass("Example", code, 0, code.length);
    // uses the dynamically generated class to print 'HelloWorld'
    exampleClass.getMethods()[0].invoke(null, new Object[] { null });
}