Question

在我的项目中，我有许多通过套接字进行通信的多线程进程。我发送一个hashmap，更新它，然后再发送一个问题。我没有更新第二次发送后得到的地图值。我在这个示例类中重现了这个问题：

package test;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.Serializable;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.HashMap;

public class Test {
    //TEST

        static class MyKey implements Serializable{
            String nome;
            String nomeM;
            int altro;
            public MyKey(String nome, String nomeM, int altro) {
                super();
                this.nome = nome;
                this.nomeM = nomeM;
                this.altro = altro;
            }
            @Override
            public int hashCode() {
                final int prime = 31;
                int result = 1;
                result = prime * result + ((nome == null) ? 0 : nome.hashCode());
                result = prime * result + ((nomeM == null) ? 0 : nomeM.hashCode());
                return result;
            }
            @Override
            public boolean equals(Object obj) {
                if (this == obj)
                    return true;
                if (obj == null)
                    return false;
                if (getClass() != obj.getClass())
                    return false;
                MyKey other = (MyKey) obj;
                if (nome == null) {
                    if (other.nome != null)
                        return false;
                } else if (!nome.equals(other.nome))
                    return false;
                if (nomeM == null) {
                    if (other.nomeM != null)
                        return false;
                } else if (!nomeM.equals(other.nomeM))
                    return false;
                return true;
            }

        }
        static class MyValue implements Serializable{
            int num;
            boolean bool;
            public MyValue(int num, boolean bool) {
                super();
                this.num = num;
                this.bool = bool;
            }
            public String toString() {
                return num + " " + bool;
            }
        }

        public static void main(String [] args) {
            final int port = 9876;
            final MyKey myKey = new MyKey("foo","bar",42);
            Thread writer = new Thread(new Runnable() {
                public void run() {
                    ServerSocket ss = null;
                    try {
                        ss = new ServerSocket(port);

                        ObjectOutputStream oos = new ObjectOutputStream(ss.accept().getOutputStream());

                        HashMap<MyKey,MyValue> map = new HashMap<>();

                        map.put(myKey, new MyValue(1,false));

                        System.out.println("writer step 1: "+map.get(myKey).toString());

                        oos.writeObject(map);
                        oos.flush();

                        map.put(myKey, new MyValue(0,true));


                        System.out.println("writer step 2: "+map.get(myKey).toString());


                        oos.writeObject(map);
                        oos.flush();

                        oos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            });
            Thread reader = new Thread(new Runnable() {
                public void run() {
                    try {
                        Socket s = new Socket("localhost",port);
                        ObjectInputStream ois = new ObjectInputStream(s.getInputStream());

                        HashMap<MyKey,MyValue> map = (HashMap<MyKey,MyValue>) ois.readObject();

                        System.out.println("reader step 1: "+map.get(myKey).toString());

                        map = (HashMap<MyKey,MyValue>) ois.readObject();

                        System.out.println("reader step 2: "+map.get(myKey).toString());

                        ois.close();
                        s.close();
                    } catch (UnknownHostException e) {
                        e.printStackTrace();
                    } catch (IOException e) {
                        e.printStackTrace();
                    } catch (ClassNotFoundException e) {
                        e.printStackTrace();
                    }
                }
            });

            writer.start();
            reader.start();
        }
        //FINE TEST
}

这就是我得到的：

writer step 1: 1 false
writer step 2: 0 true
reader step 1: 1 false
reader step 2: 1 false

我也尝试将地图包装在另一个类中，但我没有成功。

我缺少什么？

Answer 1

这是因为你没有在ObjectOutputStream上调用reset()之前在流中写入相同的对象（这里是你的地图），所以默认它认为它已经在流中了为什么你继续看到以前的状态。

重置将忽略已写入的任何对象的状态流。状态重置为与新ObjectOutputStream相同。流中的当前点被标记为重置，因此相应的ObjectInputStream将在同一点重置。先前写入流的对象不会被称为已经在流中。它们将再次写入流中。

试试这个：

// Call reset before writing your map for the second time
oos.reset();
// Write the map
oos.writeObject(map);

<强>输出：

writer step 1: 1 false
writer step 2: 0 true
reader step 1: 1 false
reader step 2: 0 true

序列化的hashmap未更新

1 个答案: