3

我正在尝试了解课程的运作方式。我正在尝试使用此代码向我的班级添加最终字段

    dout.writeShort(1);//field count
    dout.writeShort(Modifier.PUBLIC|Modifier.STATIC|Modifier.FINAL);//modifiers
    dout.writeShort(utfConstant("jjj"));//name
    dout.writeShort(utfConstant("I"));//signature
    dout.writeShort(1);//attribute count
    dout.writeShort(utfConstant("ConstantValue"));//constant value attribute
    dout.writeShort(2);//size of attribute
    dout.writeShort(intConstant(8));//value

但是当我尝试编译它时出现此错误

Exception in thread "main" java.lang.ClassFormatError: Invalid ConstantValue field attribute length 131082 in class file Test
    at java.lang.ClassLoader.defineClass1(Native Method)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:791)
    at java.lang.ClassLoader.defineClass(ClassLoader.java:634)
    at Bytecode.BytecodeTest$BytecodeClassLoader.buildClass(BytecodeTest.java:161)
    at Bytecode.BytecodeTest.makeClass(BytecodeTest.java:39)
    at Bytecode.BytecodeTest.buildClass(BytecodeTest.java:24)
    at Bytecode.BytecodeTest.main(BytecodeTest.java:17)

这是我的其他代码

private void writeConstantPool(DataOutputStream dout) throws IOException
    {
        dout.writeShort(poolIndex);

        for (Data data : poolMap) 
        {
            int tag = (byte) data.getData()[0];
            dout.writeByte(tag);

            switch (tag) 
            {
            case CONSTANT_Utf8:
                dout.writeUTF((String) data.getData()[1]);
                break;
            case CONSTANT_Class:
                dout.writeShort((Integer) data.getData()[1]);
                break;
            case CONSTANT_Integer:
                dout.writeInt((Integer) data.getData()[1]);
                break;
            default:
                throw new RuntimeException();
            }
        }
    }

    private int utfConstant(String s)
    {
        return constant(CONSTANT_Utf8, s);
    }   

    private int intConstant(int i)
    {
        return constant(CONSTANT_Integer, i);
    }

    private int classConstant(String s) 
    {
        int classNameIndex = utfConstant(s.replace('.', '/'));
        return constant(CONSTANT_Class, classNameIndex);
    }

    private int constant(Object... data) 
    {
        Data constantData = new Data(data);

        if (poolMap.contains(constantData))
            return poolMap.indexOf(constantData)+1;

        poolMap.add(poolIndex-1, constantData);
        return poolIndex++;
    }

    private final Stack<Data> poolMap = new Stack<Data>();
    private int poolIndex = 1;

    private static class Data
    {
        private Object[] data;

        public Data(Object... data)
        {
            this.data = data;
        }

        public Object[] getData()
        {
            return data;
        }

        public boolean equals(Object o)
        {           
            if(o instanceof Data)
            {
                Data other = (Data) o;
                return Arrays.equals(data, other.getData());
            }

            return false;
        }
    }

我这样做的方法是生成所有方法和字段，然后生成常量池，然后我将常量池放在方法和字段之前的字节数组中。

谁能告诉我我做错了什么，如有必要，我可以显示更多代码，另外我认为问题可能出在 intConstant 或常量值属性上。

在用字节码编辑器查看这个之后，看起来 intConstant 方法工作正常，所以我认为它是不工作的字段代码。我还在字节码编辑器中查看了一个常量，它看起来和我一样困惑。

4

1 回答 1

2

I believe the length of an attribute is supposed to be a 32-bit integer, not a 16-bit short.

于 2013-06-23T15:20:43.510 回答