套接字中的Java堆内存错误

Question

I am trying to open a socket and listen. Clients written in PHP will then send XML requests. At the moment I am just send the string "test" to it and I am getting a Memory Heap Error.

Here is my java code for the server:

import java.io.DataInputStream;
import java.io.IOException;
import java.net.ServerSocket;
import java.net.Socket;

public class main {

    /**
     * @param args
     */
    public static void main(String[] args) {
        server();

    }

    public static void server() {
        ServerSocket MyService = null;
        try {
            MyService = new ServerSocket(3030);
        }
        catch (IOException e) {
            System.out.println(e);
        }

        Socket serviceSocket = null;
        try {
            serviceSocket = MyService.accept();
        }
        catch (IOException e) {
            System.out.println(e);
        }

        DataInputStream in;
        try {
            in = new DataInputStream(serviceSocket.getInputStream());
            System.out.println("DEV STEP 1");
            int len = in.readInt();
            System.out.println(len);
            byte[] xml = new byte[len];
            in.read(xml, 0, len);
            //System.out.print(xml.toString());
            //Document doc = builder.parse(new ByteArrayInputStream(xml));

        }
        catch (IOException e) {
            System.out.println(e);
        }

    }

}

The error I am getting is:

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
    at main.server(main.java:39)
    at main.main(main.java:12)

I have done a search and there are plenty of explanations of this error on here, however I can not work out why when I am sending a 4 letter String len is 1952805748.

Answer 1

Well you are getting the out of memory error because the len is so huge. If you are sending the data as characters and then doing a readInt() on it, then that's what's causing your problem. You need to read the data as characters.

Your numeric valid is probably the binary for the string "test". You should just read a string from the InputStream, not sure why you need a DataInputStream as that's something that supports reading binary, etc, which is not what you are doing. Just use a BufferedInputStream and then do a normal read on it.

Answer 2

To expand on Francis Upton's answer, you are getting a heap exception because you are trying to read n bytes from the incoming socket stream, where n represents the totally arbitrary integer you read at the beginning of your processing loop. And the reason I call it totally arbitrary is because you never actually sent a separate int in your client code. So your code is simply reading an int from whatever is in the first 4 bytes of the input stream, which could be anything at all.

Take a look at IOUtils in Apache Commons IO , it contains nice methods for reading an entire data stream in one shot ( toByteArray , toString , etc).