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package com.loocme.sys.util;

/**
 * class类修改器
 * 
 * @author loocme
 *
 */
public class ClassModfier implements java.io.Serializable
{

    private static final long serialVersionUID = 1L;

    private static final int CONSTANT_POOL_COUNT_INDEX = 8;

    private static final int CONSTANT_UTF_8_INFO = 1;

    private static final int[] CONSTANT_ITEM_LENGTH = {-1, -1, 5, -1, 5, 9, 9,
            3, 3, 5, 5, 5, 5};

    private static final int U_1 = 1;
    private static final int U_2 = 2;

    private byte[] classByte;

    public ClassModfier(byte[] classByte)
    {
        this.classByte = classByte;
    }

    public byte[] modifyUTF8Constant(String oldStr, String newStr)
    {
        int cpc = this.getConstantPoolCount();
        int offset = CONSTANT_POOL_COUNT_INDEX + U_2;
        for (int i = 0; i < cpc; i++)
        {
            int tag = ByteUtil.bytes2Int(this.classByte, offset, U_1);
            if (CONSTANT_UTF_8_INFO == tag)
            {
                int len = ByteUtil.bytes2Int(this.classByte, offset + U_1, U_2);
                offset += (U_1 + U_2);
                String str = ByteUtil.bytes2String(this.classByte, offset, len);
                if (str.equalsIgnoreCase(oldStr))
                {
                    byte[] strBytes = ByteUtil.string2Bytes(newStr);
                    byte[] strLen = ByteUtil.int2Byte(newStr.length(), U_2);
                    this.classByte = ByteUtil.bytesReplace(this.classByte,
                            offset - U_2, U_2, strLen);
                    this.classByte = ByteUtil.bytesReplace(this.classByte,
                            offset, len, strBytes);
                    return this.classByte;
                }
                else
                {
                    offset += len;
                }
            }
            else
            {
                offset += CONSTANT_ITEM_LENGTH[tag];
            }
        }
        return this.classByte;
    }

    private int getConstantPoolCount()
    {
        return ByteUtil
                .bytes2Int(this.classByte, CONSTANT_POOL_COUNT_INDEX, U_2);
    }
}