java class檔案解析

將java class位元組碼檔案按照不同的區域進行解析處理。

import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.util.Arrays;

/**
 * Created by dezhonger on 2020/09/26
 * <p>
 * javaClass檔案解析
 */
public class ClazzResolve {

    public static void main(String[] args) {
        File file = new File("E:/深入剖析class檔案結構/第一章/example/Hello.class");
//        File file = new File("E:\\Netease\\pri\\target\\classes/Hello.class");
        InputStream in = null;
        try {
            in = new FileInputStream(file);
            showAvailableBytes(in);

            //讀取魔數
            readMagicNumber(in);

            //讀取版本號
            showAvailableBytes(in);
            readVersion(in);

            //讀取常量池
            showAvailableBytes(in);
            readConstantPool(in);

            //讀取access flag(訪問控制符)
            showAvailableBytes(in);
            readAccessFlag(in);

            //this class
            readThisClass(in);

            //superclass
            readSuperClass(in);

            //interface
            readInterface(in);

            //field
            readField(in);

            //method
            readMethod(in);

            //attribute
            readAttribute(in);

            showAvailableBytes(in);
            in.close();
        } catch (Exception e) {
            e.printStackTrace();
        }

    }

    private static void readInterface(InputStream in) {
        byte[] read = read(in, 2);
        int size = (read[0] << 8) + read[1];
        System.out.println("介面數量 " +size);
        for (int i = 0; i < size; i++) {
            read(in, 2);
        }
    }

    private static void readAttribute(InputStream in, int sz) {
        //attribute_info[sz]
        for (int k = 0; k < sz; k++) {
            read(in, 2);
            byte[] f = read(in, 4);
            int t = (f[0] << 24) + (f[1] << 16) + (f[2] << 8) + f[3];
            read(in, t);
        }
    }

    private static void readAttribute(InputStream in) {
        byte[] read = read(in, 2);
        int size = (read[0] << 8) + read[1];
        System.out.println("屬性數量 " +size);
        readAttribute(in, size);
    }

    private static void readMethod(InputStream in) {
        int len = 2;
        byte[] read = read(in, len);
        int size = (read[0] << 8) + read[1];
        System.out.println("方法數量 " +size);
        for (int i = 0; i < size; i++) {
            //access_flags
            read(in, 2);
            //name_index
            read(in, 2);
            //descriptor_index
            read(in, 2);

            //attribute_count
            byte[] s = read(in, 2);
            int sz = (s[0] << 8) + s[1];
            //attribute_info[sz]
            readAttribute(in, sz);

        }
    }

    private static void readField(InputStream in) {
        int len = 2;
        byte[] read = read(in, len);
        int size = (read[0] << 8) + read[1];
        for (int i = 0; i < size; i++) {
            //access_flags
            read(in, 2);
            //name_index
            read(in, 2);
            //descriptor_index
            read(in, 2);

            //attribute_count
            byte[] s = read(in, 2);
            int sz = (s[0] << 8) + s[1];
            //attribute_info[sz]
            readAttribute(in, sz);

        }

    }

    private static void readSuperClass(InputStream in) {
        read(in, 2);

    }

    private static void readThisClass(InputStream in) {
        read(in, 2);
    }

    private static void readAccessFlag(InputStream in) {
        read(in, 2);
    }


    private static void readConstantPool(InputStream in) {
        int len = 2;

        byte[] read = read(in, len);


        int size = (read[0] << 8) + read[1];
        int tagLen = 1;
        for (int i = 0; i < size - 1; i++) {
            byte[] readTag = read(in, tagLen);
            switch (readTag[0]) {
                case 1://字串
                    byte[] utf8Length = read(in, 2);
                    read(in, (utf8Length[0] << 8) + utf8Length[1]);
                    break;
                case 3: case 4://int float
                    read(in, 4);
                    break;
                case 5: case 6://long double
                    read(in, 8);
                    break;
                case 7://Class
                    read(in, 2);
                    break;
                case 8://String
                    read(in, 2);
                    break;
                case 9: case 10: case 11://fieldref methodref interfaceref
                    read(in, 2);
                    read(in, 2);
                    break;
                case 12://NameAndType
                    read(in, 2);
                    read(in, 2);
                    break;
                case 15: case 16: case 18:
                    read(in, 2);
                    read(in, 2);
                    break;
                default:
                    System.err.println("出錯了" + readTag[0]);
                    break;

            }
        }

    }

    private static void readVersion(InputStream in) {
        int len = 4;
        read(in, len);
    }

    private static void readMagicNumber(InputStream in) {
        int len = 4;
        read(in, len);
    }

    private static byte[] read(InputStream in,int len) {
        byte[] bytes = new byte[len];
        try {
            in.read(bytes);
            String[] res = new String[len];
            for (int i = 0; i < len; i++){
                res[i] = Integer.toHexString(Byte.toUnsignedInt(bytes[i]));
                if (res[i].length() == 1) res[i] = "0" + res[i];
//                System.out.println(Integer.toHexString(Byte.toUnsignedInt(b)));
            }
            System.out.println(Arrays.toString(res));
        } catch (IOException e) {
            e.printStackTrace();
        }
        return bytes;
    }

    /**
     * 顯示輸入流中還剩的位元組數
     */
    private static void showAvailableBytes(InputStream in) {
        try {
            System.out.println("當前位元組輸入流中的位元組數為:" + in.available());
        } catch (IOException e) {
            e.printStackTrace();
        }
    }


}