您可以使用 Apache 软件基金会的 BCEL。使用此工具,您可以生成类似汇编程序的代码,但它是带有 BCEL API 的 Java。您可以了解如何生成中间语言代码(在本例中为字节代码)。
简单示例
-
用这个函数创建一个Java类:
public String maxAsString(int a, int b) {
if (a > b) {
return Integer.valueOf(a).toString();
} else if (a < b) {
return Integer.valueOf(b).toString();
} else {
return "equals";
}
}
现在用这个类运行 BCELifier
BCELifier bcelifier = new BCELifier("MyClass", System.out);
bcelifier.start();
您可以在控制台上看到整个类的结果(如何构建字节码 MyClass.java)。该函数的代码是这样的:
private void createMethod_1() {
InstructionList il = new InstructionList();
MethodGen method = new MethodGen(ACC_PUBLIC, Type.STRING, new Type[] { Type.INT, Type.INT }, new String[] { "arg0", "arg1" }, "maxAsString", "MyClass", il, _cp);
il.append(InstructionFactory.createLoad(Type.INT, 1)); // Load first parameter to address 1
il.append(InstructionFactory.createLoad(Type.INT, 2)); // Load second parameter to adress 2
BranchInstruction if_icmple_2 = InstructionFactory.createBranchInstruction(Constants.IF_ICMPLE, null); // Do if condition (compare a > b)
il.append(if_icmple_2);
il.append(InstructionFactory.createLoad(Type.INT, 1)); // Load value from address 1 into the stack
il.append(_factory.createInvoke("java.lang.Integer", "valueOf", new ObjectType("java.lang.Integer"), new Type[] { Type.INT }, Constants.INVOKESTATIC));
il.append(_factory.createInvoke("java.lang.Integer", "toString", Type.STRING, Type.NO_ARGS, Constants.INVOKEVIRTUAL));
il.append(InstructionFactory.createReturn(Type.OBJECT));
InstructionHandle ih_13 = il.append(InstructionFactory.createLoad(Type.INT, 1));
il.append(InstructionFactory.createLoad(Type.INT, 2));
BranchInstruction if_icmpge_15 = InstructionFactory.createBranchInstruction(Constants.IF_ICMPGE, null); // Do if condition (compare a < b)
il.append(if_icmpge_15);
il.append(InstructionFactory.createLoad(Type.INT, 2));
il.append(_factory.createInvoke("java.lang.Integer", "valueOf", new ObjectType("java.lang.Integer"), new Type[] { Type.INT }, Constants.INVOKESTATIC));
il.append(_factory.createInvoke("java.lang.Integer", "toString", Type.STRING, Type.NO_ARGS, Constants.INVOKEVIRTUAL));
il.append(InstructionFactory.createReturn(Type.OBJECT));
InstructionHandle ih_26 = il.append(new PUSH(_cp, "equals")); // Return "equals" string
il.append(InstructionFactory.createReturn(Type.OBJECT));
if_icmple_2.setTarget(ih_13);
if_icmpge_15.setTarget(ih_26);
method.setMaxStack();
method.setMaxLocals();
_cg.addMethod(method.getMethod());
il.dispose();
}