目录

• 无符号字节转为int
• Java中字节转为int
• 字节缓冲流
  • 基本知识
  • String与ByteBuffer转换

无符号字节转为int

https://tool.oschina.net/hexconvert 在线进制转换

场景描述：Java 中基本类型都是有符号数值，如果接收到了 C/C++ 处理的无符号数值字节流，将出现转码错误。

//解析webscoket传输得二进制数据，因为二进制数据传输的是uint32无符号整数，把有符号的字节转为正常的
//uint32代表无符号整数，只能存正整数，在内存中占4个字节，byte[4]，0到4294967295，Java中int为32位有符号整数，占4字节，-2147483648到2147483648

/**
 * 无符号字节转为int
 * @param buf
 * @return
 */
public static long bytes2int(byte[] buf){
    long anUnsignedInt = 0;
    int firstByte = 0;
    int sceondByte = 0;
    int thirdByte = 0;
    int fourthByte = 0;
    int index = 0;
    firstByte = (0x000000FF & ((int) buf[index+3]));
    sceondByte = (0x000000FF & ((int) buf[index+2]));
    thirdByte = (0x000000FF & ((int) buf[index+1]));
    fourthByte = (0x000000FF & ((int) buf[index]));
    anUnsignedInt = ((long) (firstByte << 24 | sceondByte << 16 | thirdByte << 8 | fourthByte)) & 0xFFFFFFFFL;
    return anUnsignedInt ;
}

Java中字节转为int

public static int byteArrayToInt(byte[] bytes) {
    int n = 0;
    for (int i = 0; i < 4; i++) {
        n += bytes[i] << i*8;
    }
    return n;
}

字节缓冲流

基本知识

//1.分配一个指定大小的缓冲区
ByteBuffer buf = ByteBuffer.allocate(1024);
System.out.println(buf.position); //0
System.out.println(buf.limit); //1024
System.out.println(buf.capacity); //1024
System.out.println(buf.mark); 

//2.利用put()方法进行存储数据
String str = "hello nio";
buf.put(str.getBytes());
System.out.println(buf.position); //9
System.out.println(buf.limit); //1024
System.out.println(buf.capacity); //1024
System.out.println(buf.mark); 

//3.切换读取数据的模式
buf.flip();
System.out.println(buf.position); //0
System.out.println(buf.limit); //1024
System.out.println(buf.capacity); //1024
System.out.println(buf.mark);

//4.利用get()方法读取数据
byte[] dst = new byte[buf.limit()];
buf.get(dst);
System.out.println(new String(dst, 0, dst.lenth));

System.out.println(buf.position); //9
System.out.println(buf.limit); //9
System.out.println(buf.capacity); //1024
System.out.println(buf.mark

String与ByteBuffer转换

import java.nio.ByteBuffer;  
import java.nio.CharBuffer;  
import java.nio.charset.Charset;  
import java.nio.charset.CharsetDecoder;  
  
public class TopNTool {  
    /** 
     * String 转换 ByteBuffer 
     * @param str 
     * @return 
     */  
    public static ByteBuffer getByteBuffer(String str) {  
        return ByteBuffer.wrap(str.getBytes());  
    }  
  
    /** 
     * ByteBuffer 转换 String 
     * @param buffer 
     * @return 
     */  
    public static String getString(ByteBuffer buffer) {  
        Charset charset = null;  
        CharsetDecoder decoder = null;  
        CharBuffer charBuffer = null;  
        try {  
            charset = Charset.forName("UTF-8");  
            decoder = charset.newDecoder();  
            // charBuffer = decoder.decode(buffer);//用这个的话，只能输出来一次结果，第二次显示为空  
            charBuffer = decoder.decode(buffer.asReadOnlyBuffer());  
            return charBuffer.toString();  
        }  
        catch (Exception ex) {  
            ex.printStackTrace();  
            return "";  
        }  
    }  
}