java Socket无法完全接收返回内容的解决方案
最近在使用Socket通讯时，遇到了接收内容不全（返回内容 = 4字节报文长度 + 内容主体）的问题：客户端发送请求数据，服务器明明返回了73个字节内容，但客户端有时能全部接收，但有时却只能返回4个字节。
一开始是怀疑服务器返回有问题，但使用调试工具连续测试了很多次，结果显示：服务器的确每次都返回了73个字节内容。那很明显了，问题出现在客户端代码上。
错误现象
再来看看调试工具结果：
让我们来看看客户端代码，调用方法如下：（该方法适用于返回报文前两个字节表示长度的情况：2字节报文长度 + 内容主体）
public static void test() {
SocketClient client = new SocketClient();
// 建立socket对象
int iret = client.connect("192.168.1.105", 1234);
if (iret == 0) {
// 发送数据
client.write("helloworld".getBytes());
// 接收数据
byte data[] = client.read();
if ((data != null) && (data.length != 0)) {
// 处理接收结果
Utils.print("响应报文字节数组---->" + Arrays.toString(data));
}
}
}
SocketClient.java源码：
public class SocketClient {
// 存储接收数据
private byte m_buffer[] = new byte[0x10000];
private Socket m_socket;
private InputStream m_inputstream;
private OutputStream m_outputstream;
private BufferedInputStream m_bufferedinputstream;
private BufferedOutputStream m_bufferedoutputstream;
private boolean connected;
public int connect(String host, int port) {
try {
SocketAddress socketAddress = new InetSocketAddress(host, port);
m_socket = new Socket();
m_socket.connect(socketAddress, 5000);
m_socket.setSoTimeout(60000);
m_inputstream = m_socket.getInputStream();
m_bufferedinputstream = new BufferedInputStream(m_inputstream);
m_outputstream = m_socket.getOutputStream();
m_bufferedoutputstream = new BufferedOutputStream(m_outputstream);
} catch (Exception e) {
return -1;
}
connected = true;
return 0;
}
/**
* 发送请求数据
*
* @param data
* @param start
* @param end
* @return
*/
public int write(byte data[]) {
if (data == null || data.length == 0 || !connected) {
return 0;
}
try {
m_bufferedoutputstream.write(data, 0, data.length);
m_bufferedoutputstream.flush();
} catch (Exception e) {
return -1;
}
return 0;
}
/**
* 读取返回数据
*
* @return
*/
public byte[] read() {
if (!connected) {
return null;
}
int len = -1;
try {
// 长度不正确，有时返回4，有时返回73
len = m_bufferedinputstream.read(m_buffer, 0, 0x10000);
} catch (Exception e) {
len = 0;
}
if (len != -1) {
return null;
} else {
byte ret[] = new byte[len];
for (int i = 0; i < len; i++) {
ret[i] = m_buffer[i];
}
return ret;
}
}
}
通过代码调试，发现问题出现在inputsream.read方法上，java API对其描述如下：
int java. io. BufferedInputStream.read( byte[] buffer, int offset, int byteCount) throws IOException
Reads at most byteCount bytes from this stream and stores them in byte array buffer starting at offset offset. Returns the number of bytes actually read or -1 if no bytes were read and the end of the stream was encountered. If all the buffered bytes have been used, a mark has not been set and the requested number of bytes is larger than the receiver's buffer size, this implementation bypasses the buffer and simply places the results directly into buffer.
Overrides: read(...) in FilterInputStream
Parameters:
buffer the byte array in which to store the bytes read.
offset the initial position in buffer to store the bytes read from this stream.
byteCount the maximum number of bytes to store in buffer.
Returns:
the number of bytes actually read or -1 if end of stream.
Throws:
IndexOutOfBoundsException - if offset < 0 or byteCount < 0, or if offset + byteCount is greater than the size of buffer.
IOException - if the stream is already closed or another IOException occurs.
引起错误原因在于
客户端在发送数据后，过快地执行read操作，而这时服务端尚未完全返回全部内容，因此只能读到部分字节。于是换了个思路：
public class SocketClient {
private Socket m_socket;
private InputStream m_inputstream;
private OutputStream m_outputstream;
private BufferedInputStream m_bufferedinputstream;
private BufferedOutputStream m_bufferedoutputstream;
private boolean connected;
public int connect(String host, int port) {
try {
SocketAddress socketAddress = new InetSocketAddress(host, port);
m_socket = new Socket();
m_socket.connect(socketAddress, 5000);
m_socket.setSoTimeout(60000);
m_inputstream = m_socket.getInputStream();
m_bufferedinputstream = new BufferedInputStream(m_inputstream);
m_outputstream = m_socket.getOutputStream();
m_bufferedoutputstream = new BufferedOutputStream(m_outputstream);
} catch (Exception e) {
return -1;
}
connected = true;
return 0;
}
/**
* 发送请求数据
*
* @param data
* @param start
* @param end
* @return
*/
public int write(byte data[]) {
if (data == null || data.length == 0 || !connected) {
return 0;
}
try {
m_bufferedoutputstream.write(data, 0, data.length);
m_bufferedoutputstream.flush();
} catch (Exception e) {
return -1;
}
return 0;
}
/**
* 读取返回数据
*
* @return
*/
public byte[] read() {
if (!connected) {
return null;
}
try {
return readStream(m_bufferedinputstream);
} catch (Exception e) {
return null;
}
}
/**
* @功能 读取流
* @param inStream
* @return 字节数组
* @throws Exception
*/
public static byte[] readStream(InputStream inStream) throws Exception {
ByteArrayOutputStream outSteam = new ByteArrayOutputStream();
byte[] buffer = new byte[1024];
int len = -1;
while ((len = inStream.read(buffer)) != -1) {
outSteam.write(buffer, 0, len);
}
outSteam.close();
inStream.close();
return outSteam.toByteArray();
}
public static void test() {
SocketClient client = new SocketClient();
// 建立socket对象
int iret = client.connect("192.168.1.105", 1234);
if (iret == 0) {
// 发送数据
client.write("helloworld".getBytes());
// 接收数据
byte data[] = client.read();
if ((data != null) && (data.length != 0)) {
// 处理接收结果
Utils.print("响应报文字节数组---->" + Arrays.toString(data));
}
}
}
}
测试通过.....
可参考以下解决思路
protected byte[] readMessage(BufferedInputStream is) throws IOException {
// MyLog.d(TAG,"=======>readMessage--inputStream=" );
int offset = 0;
int messageStartOffset = -1;
int wait = 0;
int messageEndOffset = -1;
int findStartOffset = -1;
while(messageEndOffset==-1||(messageEndOffset+2)>offset){
if(is.available()==0){
try {
Thread.sleep(MESSAGE_WAIT_INTERVAL);
wait += MESSAGE_WAIT_INTERVAL;
} catch (InterruptedException ex) {
}
if(wait>=MESSAGE_OVERTIME){
//超时错误
throw new RuntimeException(EXCEPTION_TIMEOUT);
}
continue;
}
offset += is.read(messageBuffer, offset, is.available());//读出数据
TestMessage.showBytes(messageBuffer, 0, offset, "MESSAGE");
if(messageStartOffset==-1){ //未找到报文头
if(findStartOffset<0)
findStartOffset = 0;
messageStartOffset = findStartOffset(messageBuffer, findStartOffset, offset);//查找报文头
MyLog.e(TAG, "messageStartOffset="+messageStartOffset);
if(messageStartOffset>=0){//找到报文头
if(messageStartOffset<2){
//报文错误
throw new RuntimeException(EXCEPTION_MSG_PARSE_ERROR);
}else{
int iMessageLength = ((messageBuffer[messageStartOffset-2]&0xff)<<8)+
(messageBuffer[messageStartOffset-1]&0xff);
// MyLog.e(TAG, "iMessageLength="+iMessageLength);
int ignoreInvalidLength = messageStartOffset-4;
messageEndOffset = iMessageLength + ignoreInvalidLength;
// MyLog.e(TAG, "messageStartOffset="+messageStartOffset);
MyLog.e(TAG, "messageEndOffset="+messageEndOffset);
如果想要让程序保证读取到count个字节，最好用以下代码：
int count = 100;
byte[] b = new byte[count];
int readCount = 0; // 已经成功读取的字节的个数
while (readCount < count) {
readCount += inStream.read(b, readCount, count - readCount);
}
这样就能保证读取100个字节，除非中途遇到IO异常或者到了数据流的结尾情况！
以上为个人经验，希望能给大家一个参考，也希望大家多多支持脚本之家。
相关文章
这篇文章主要为大家详细介绍了java实现简单图书管理系统，文中示例代码介绍的非常详细，具有一定的参考价值，感兴趣的小伙伴们可以参考一下2022-03-03
这篇文章主要介绍了Java定时清理过期文件的实例代码，非常不错，具有一定的参考借鉴价值 ,需要的朋友可以参考下2018-12-12
这篇文章主要介绍了spring Retryable注解实现重试详解，具有很好的参考价值，希望对大家有所帮助。一起跟随小编过来看看吧2020-09-09
Spring Data是一个流行的数据访问框架,本文主要介绍了Spring Data中domain模块的使用,并展示如何使用它来优化我们的数据访问层,具有一定的参考价值,感兴趣的可以了解一下2024-03-03
本篇文章主要介绍了springMVC的生命周期详解，小编觉得挺不错的，现在分享给大家，也给大家做个参考。一起跟随小编过来看看吧2017-03-03
这篇文章主要介绍了java编程多线程并发处理实例解析，分享了相关代码示例，小编觉得还是挺不错的，具有一定借鉴价值，需要的朋友可以参考下2018-01-01
Java根据URL下载文件到本地的2种方式(大型文件与小型文件)
这篇文章主要给大家介绍了关于Java根据URL下载文件到本地的2种方式,分别是大型文件与小型文件,避免内存溢出OOM,文中通过代码介绍的非常详细,需要的朋友可以参考下2024-01-01
这篇文章主要为大家详细介绍了java实现图片无损任意角度旋转，具有一定的参考价值，感兴趣的小伙伴们可以参考一下2019-02-02
java中的new关键字是实例化对象，接下来本文通过一个案例给大家讲解Java中的 new 关键字，感兴趣的朋友可以参考下2016-08-08
这篇文章主要为大家介绍了Java OpenCV利用K最邻近（KNN，K-NearestNeighbor）分类算法实现图像背景移除的示例代码，需要的可以参考一下2022-01-01
最新评论