Java中使用ByteBuffer处理tcp粘包

分类：Android, Java, Java语言阅读 (3,322)

8月 222019

转载请注明原文地址：http://bcoder.com/java/process-sticky-data-in-java-by-using-bytebuffer

一、通讯数据格式

通讯协议的约定格式如下：

每一个数据包的长度不固定，但是前四个字节代表的意义是固定的

数据的长度取决于第３个字段的值

名称	长度	其他说明
协议头	2字节	固定的两个字节，用以给协议分段
数据类型	1字节	数据内容的类型，用以区别多种内容
数据长度	1字节	后面数据内容的长度，1字节可表示最大长度是255
数据	n字节	n取决于上一个字节中的数值
…
…
…

二、处理的难点

长度不固定，解析每一组数据时需要先想办法获取数据的长度
如果发送速度很快，收到一包可能有多组数据，需要一个while循环处理收到的一包的数据（这也就是粘包处理的初衷）
收到一包数据（本例中使用1024长度的缓冲区接收）可能将某个数据包截成两截，当前缓冲区未解析完的要保留下来，否则会丢数据

三、处理流程图

四、代码

在while(true)里面是读取tcp数据和进行粘包处理的代码

    class ReceiveThread extends Thread{
        private boolean mReadSucc ;

        private Handler mainThread = new Handler(Looper.getMainLooper());

        @Override
        public void run() {
            super.run();

            int readlen = 0;
            byte[] buffer = new byte[1024];
            ByteBuffer stickyBuffer = ByteBuffer.allocate(4096);
            boolean foundHeader = false;

            while (true){
                if(!mIsServiceRunning){
                    break;
                }

                try {
                    sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }

                try {
                    mReadSucc = false;
                    readlen = mInputStream.read(buffer);
                    mReadSucc = true;
                } catch (IOException e) {
                    e.printStackTrace();
                }

                if(!mReadSucc || readlen == 0){
                    continue;
                }

                stickyBuffer.limit(4096);
                stickyBuffer.put(buffer, 0, readlen);
                stickyBuffer.flip();

                while (true){
                    if(!stickyBuffer.hasRemaining()){
                        stickyBuffer.compact();
                        stickyBuffer.clear();
                        break;
                    }

                    stickyBuffer.mark();
                    if(stickyBuffer.remaining() < 4){
                        int remaining = stickyBuffer.remaining();
                        stickyBuffer.compact();
                        stickyBuffer.position(remaining);
                        stickyBuffer.limit(remaining);
                        foundHeader = false;
                        break;
                    } else {
                        short magicno = stickyBuffer.getShort();

                        if(magicno != (short) 0xC0DE){
                            continue;
                        } else {
                            foundHeader = true;
                        }
                    }

                    if (foundHeader){
                        int datatype = stickyBuffer.get() & 0xFF;
                        int datalen = stickyBuffer.get() & 0xFF;

                        if(stickyBuffer.remaining() < datalen) {
                            stickyBuffer.reset();
                            stickyBuffer.compact();
                            break;
                        } else {
                            byte[] databuf = new byte[datalen];
                            stickyBuffer.get(databuf);
                            processSerialData(datatype, databuf);
                        }
                    }
                }
            }
        }

class ReceiveThread extends Thread{

private boolean mReadSucc ;

private Handler mainThread = new Handler(Looper.getMainLooper());

@Override

public void run() {

super.run();

int readlen = 0;

byte[] buffer = new byte[1024];

ByteBuffer stickyBuffer = ByteBuffer.allocate(4096);

boolean foundHeader = false;

while (true){

if(!mIsServiceRunning){

break;

}

try {

sleep(1);

} catch (InterruptedException e) {

e.printStackTrace();

}

try {

mReadSucc = false;

readlen = mInputStream.read(buffer);

mReadSucc = true;

} catch (IOException e) {

e.printStackTrace();

}

if(!mReadSucc || readlen == 0){

continue;

}

stickyBuffer.limit(4096);

stickyBuffer.put(buffer, 0, readlen);

stickyBuffer.flip();

while (true){

if(!stickyBuffer.hasRemaining()){

stickyBuffer.compact();

stickyBuffer.clear();

break;

}

stickyBuffer.mark();

if(stickyBuffer.remaining() < 4){

int remaining = stickyBuffer.remaining();

stickyBuffer.compact();

stickyBuffer.position(remaining);

stickyBuffer.limit(remaining);

foundHeader = false;

break;

} else {

short magicno = stickyBuffer.getShort();

if(magicno != (short) 0xC0DE){

continue;

} else {

foundHeader = true;

}

if (foundHeader){

int datatype = stickyBuffer.get() & 0xFF;

int datalen = stickyBuffer.get() & 0xFF;

if(stickyBuffer.remaining() < datalen) {

stickyBuffer.reset();

stickyBuffer.compact();

break;

} else {

byte[] databuf = new byte[datalen];

stickyBuffer.get(databuf);

processSerialData(datatype, databuf);

}

五、其他说明

串口通讯的粘包处理也可以使用此方法

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