Question

java Socket编程中read方法的阻塞问题，求高手解答 代码如下

import java.io.*;
import java.net.*;
class ClientDemo
{
public static void main(String[] args) throws Exception
{
Socket s = new Socket("127.0.0.1",10002);

DataOutputStream out =new DataOutputStream(s.getOutputStream());

out.write("TCP 来了".getBytes());

DataInputStream in = new DataInputStream(s.getInputStream());

byte[] buf = new byte[1024];

int len = in.read(buf);

String text = new String(buf,0,len);

System.out.println("server:"+text);

s.close();
}
}

class ServerDemo
{
public static void main(String[] args) throws Exception
{
ServerSocket ss = new ServerSocket(10002);

Socket s = ss.accept();//该方法是阻塞式的。

String ip = s.getInetAddress().getHostAddress();
System.out.println(ip+".....connected");

DataInputStream in = new DataInputStream(s.getInputStream());

byte[] buf = new byte[1024];
int len = 0;
while(( len = in.read(buf))!=-1);
{
String text = new String(buf,0,len);

System.out.println(text);
}

DataOutputStream out =new DataOutputStream(s.getOutputStream());

out.write("已收到".getBytes());

s.close();
ss.close();
}
}

Answer 1

import java.io.*;
import java.net.*;

class ClientDemo {
public static void main(String[] args) throws Exception {
Socket s = new Socket("127.0.0.1", 10002);

DataOutputStream out = new DataOutputStream(s.getOutputStream());

out.write("TCP 来了".getBytes());
out.flush();

DataInputStream in = new DataInputStream(s.getInputStream());

byte[] buf = new byte[1024];
int len = 0;
while (true) {
if ((len = in.read(buf)) != -1) {
String text = new String(buf, 0, len);
System.out.println("server:" + text);
break;
}
}

s.close();
}
}

class ServerDemo {
public static void main(String[] args) throws Exception {
ServerSocket ss = new ServerSocket(10002);

while (true) {
Socket s = ss.accept();// 该方法是阻塞式的。

String ip = s.getInetAddress().getHostAddress();
System.out.println(ip + ".....connected");

DataInputStream in = new DataInputStream(s.getInputStream());
DataOutputStream out = new DataOutputStream(s.getOutputStream());

byte[] buf = new byte[1024];
int len = 0;

if ((len = in.read(buf)) != -1) {
String text = new String(buf, 0, len);
System.out.println(text);

out.write("已收到".getBytes());
out.flush();
}

}

}
}

给你改了下

Answer 2

你想问什么

追问

开启服务端，运行客户端以后，程序阻塞了，不能往下进行了。

追答

while(( len = in.read(buf))!=-1);
注意后面一个分号。

追问

那个是我写错了，但是分号去掉以后，客户端还是继续阻塞，收不到服务器端发来的信息啊。

追答

while (in.available() > 0) {
len = in.read(buf);
String text = new String(buf, 0, len);
System.out.println(text);
}

追问

可以了，但是我的这个方法为什么会阻塞？可否解答一下？谢谢了。还有，我如果去掉while循环，一样可以实现啊？

追答

看源码啊DataInputStream的read方法。
/**
* Reads some number of bytes from the contained input stream and
* stores them into the buffer array b. The number of
* bytes actually read is returned as an integer. This method blocks
* until input data is available, end of file is detected, or an
* exception is thrown.
public final int read(byte b[]) throws IOException {
return in.read(b, 0, b.length);
}

This method blocks
* until input data is available, end of file is detected, or an
* exception is thrown.

你第一次读，就把数据读完了，接下来没有可读的了。

/**
* Returns an estimate of the number of bytes that can be read (or
* skipped over) from this input stream without blocking by the next
* caller of a method for this input stream. The next caller might be
* the same thread or another thread. A single read or skip of this
* many bytes will not block, but may read or skip fewer bytes.
*
* This method returns the result of {@link #in in}.available().
*
* @return an estimate of the number of bytes that can be read (or skipped
* over) from this input stream without blocking.
* @exception IOException if an I/O error occurs.
*/
public int available() throws IOException {
return in.available();
}