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");
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");
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});
}
public static void createEmptyArray(GeneratorAdapter adapter) {
adapter.newInstance(Types.ARRAY_IMPL);
adapter.dup();
adapter.invokeConstructor(Types.ARRAY_IMPL, Switch.INIT);
}
public static byte[] createPojo(
String className, ASMProperty[] properties, Class parent, Class[] interfaces, String srcName)
throws PageException {
className = className.replace('.', '/');
className = className.replace('\\', '/');
className = ListUtil.trim(className, "/");
String[] inter = null;
if (interfaces != null) {
inter = new String[interfaces.length];
for (int i = 0; i < inter.length; i++) {
inter[i] = interfaces[i].getName().replace('.', '/');
}
}
// CREATE CLASS
ClassWriter cw = ASMUtil.getClassWriter();
cw.visit(
Opcodes.V1_6,
Opcodes.ACC_PUBLIC,
className,
null,
parent.getName().replace('.', '/'),
inter);
String md5;
try {
md5 = createMD5(properties);
} catch (Throwable t) {
md5 = "";
t.printStackTrace();
}
FieldVisitor fv =
cw.visitField(
Opcodes.ACC_PUBLIC + Opcodes.ACC_FINAL + Opcodes.ACC_STATIC,
"_md5_",
"Ljava/lang/String;",
null,
md5);
fv.visitEnd();
// Constructor
GeneratorAdapter adapter =
new GeneratorAdapter(Opcodes.ACC_PUBLIC, CONSTRUCTOR_OBJECT, null, null, cw);
adapter.loadThis();
adapter.invokeConstructor(toType(parent, true), CONSTRUCTOR_OBJECT);
adapter.returnValue();
adapter.endMethod();
// properties
for (int i = 0; i < properties.length; i++) {
createProperty(cw, className, properties[i]);
}
// complexType src
if (!StringUtil.isEmpty(srcName)) {
GeneratorAdapter _adapter =
new GeneratorAdapter(
Opcodes.ACC_PUBLIC + Opcodes.ACC_FINAL + Opcodes.ACC_STATIC,
_SRC_NAME,
null,
null,
cw);
_adapter.push(srcName);
_adapter.returnValue();
_adapter.endMethod();
}
cw.visitEnd();
return cw.toByteArray();
}
public static void createEmptyStruct(GeneratorAdapter adapter) {
adapter.newInstance(Types.STRUCT_IMPL);
adapter.dup();
adapter.invokeConstructor(Types.STRUCT_IMPL, Page.INIT_STRUCT_IMPL);
}
