ClassFileParse.java

package main.coding_170409.jvm.loader;

import main.coding_170409.jvm.constant.*;

import java.io.UnsupportedEncodingException;

/**
 * Created by peter on 2017/4/21.
 */
public class ClassFileParse {
    public ConstantPool parse(byte[] codes) {

        ByteCodeIterator iterator = new ByteCodeIterator(codes);

        String magicNumber = iterator.nextU4ToHexString();

        if (!"cafebabe".equals(magicNumber)) {
            return null;
        }
        iterator.nextU2ToInt();
        iterator.nextU2ToInt();
        ConstantPool pool = parseConstantPool(iterator);
        return pool;
    }

    public ConstantPool parseConstantPool(ByteCodeIterator iterator) {
        int constantPoolCount = iterator.nextU2ToInt();

        ConstantPool pool = new ConstantPool();
        pool.addConstantInfo(new NullConstantInfo());
        for (int i = 1; i <= constantPoolCount - 1; i++) {
            int tag = iterator.nextU1ToInt();
            if (tag == 7) {
                int utf8Index = iterator.nextU2ToInt();
                ClassInfo classInfo = new ClassInfo(pool);
                classInfo.setUtf8Index(utf8Index);
                pool.addConstantInfo(classInfo);
            } else if (tag == 1) {
                //UTF-8 String
                int len = iterator.nextU2ToInt();
                byte[] data = iterator.getBytes(len);
                String value = null;
                try {
                    value = new String(data, "UTF-8");
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
                UTF8Info utf8Info = new UTF8Info(pool);
                utf8Info.setLength(len);
                utf8Info.setValue(value);
                pool.addConstantInfo(utf8Info);
            } else if (tag == 8) {
                StringInfo info = new StringInfo(pool);
                info.setIndex(iterator.nextU2ToInt());
                pool.addConstantInfo(info);
            } else if (tag == 9) {
                FieldRefInfo field = new FieldRefInfo(pool);
                field.setClassInfoIndex(iterator.nextU2ToInt());
                field.setNameAndTypeIndex(iterator.nextU2ToInt());
                pool.addConstantInfo(field);
            } else if (tag == 10) {
                //MethodRef
                MethodRefInfo method = new MethodRefInfo(pool);
                method.setClassInfoIndex(iterator.nextU2ToInt());
                method.setNameAndTypeIndex(iterator.nextU2ToInt());
                pool.addConstantInfo(method);
            } else if (tag == 12) {
                //Name and Type Info
                NameAndTypeInfo nameAndTypeInfo = new NameAndTypeInfo(pool);
                nameAndTypeInfo.setIndexA(iterator.nextU2ToInt());
                nameAndTypeInfo.setIndexB(iterator.nextU2ToInt());
                pool.addConstantInfo(nameAndTypeInfo);
            } else {
                throw new RuntimeException("the constant pool tag " + tag + " has not implemented");
            }
        }
        System.out.println("Finished reading Constant pool");

        return pool;
    }


}