关于对象序列化的问题

Question

//下面程序的目的是实现对像的序列化。程序运行时先看obj.txt文件中有没有以前保存的文件，如果没有的话就new 一个对像并写入obj.txt中。最后读出obj.txt中的对像并输出，但是运行时为什么会出现EOFException呢？
import java.io.*;
public class SerializableTest implements Serializable
{
String str;
public SerializableTest(String str)
{
this.str=str;
}
public static void main(String[] args)
{
FileInputStream in=null;        FileOutputStream out=null;        ObjectInputStream oin=null;        ObjectOutputStream oout=null;
        
        SerializableTest temp=null,temp2=null;
        SerializableTest obj=new SerializableTest("hello");
try{
in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);if((temp=(SerializableTest)oin.readObject())==null)
{
oin.close();
out=new FileOutputStream("obj.txt");
oout=new ObjectOutputStream(out);
oout.writeObject(obj);
oout.close();
}in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);
temp2=(SerializableTest)oin.readObject();
System.out.println(temp2.str);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}

Answer 1

因为你的文件是空的，或者是没有进行过对象序列化的文件，因此在进行oin=new ObjectInputStream(in);
时会出错，因此你需要的判断是oin==null，而不是temp=(SerializableTest)oin.readObject())==null之类的。
改成下面这样就可以了：import java.io.*;
public class SerializableTest implements Serializable
{
String str;
public SerializableTest(String str)
{
this.str=str;
}
public static void main(String[] args)
{
FileInputStream in=null;        FileOutputStream out=null;        ObjectInputStream oin=null;        ObjectOutputStream oout=null;
        
        SerializableTest temp=null,temp2=null;
        SerializableTest obj=new SerializableTest("hello");
        try{
            in=new FileInputStream("obj.txt");
            oin=new ObjectInputStream(in);
        }catch(EOFException e){
        }catch(Exception e){
            
        }
        
        try{            if(oin==null)
            {
                out=new FileOutputStream("obj.txt");
                oout=new ObjectOutputStream(out);
                oout.writeObject(obj);
                oout.close();
            }else{                
            in=new FileInputStream("obj.txt");
            oin=new ObjectInputStream(in);
            temp2=(SerializableTest)oin.readObject();
            System.out.println(temp2.str);
            }
        }catch(Exception e){
            e.printStackTrace();
        }
}
}

Answer 2

import java.io.*;
public class SerializableTest implements Serializable
{
String str;
public SerializableTest(String str)
{
this.str=str;
}
public static void main(String[] args)
{
FileInputStream in=null;        FileOutputStream out=null;        ObjectInputStream oin=null;        ObjectOutputStream oout=null;
        
        SerializableTest temp=null,temp2=null;
        SerializableTest obj=new SerializableTest("hello");
try{
File f = new File("obj.txt");
if(f.exists()){
in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);

if((temp=(SerializableTest)oin.readObject())==null){
oin.close();
out=new FileOutputStream("obj.txt");
oout=new ObjectOutputStream(out);
oout.writeObject(obj);
oout.close();
}
}


in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);
temp2=(SerializableTest)oin.readObject();
System.out.println(temp2.str);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}

Answer 3

import java.io.*;
public class SerializableTest implements Serializable
{
String str;
public SerializableTest(String str)
{
this.str=str;
}
public static void main(String[] args)
{
FileInputStream in=null;        FileOutputStream out=null;        ObjectInputStream oin=null;        ObjectOutputStream oout=null;
        
        SerializableTest temp=null,temp2=null;
        SerializableTest obj=new SerializableTest("hello");
try{
File f = new File("obj.txt");
if(f.exists()){
in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);

if((temp=(SerializableTest)oin.readObject())==null){
oin.close();
out=new FileOutputStream("obj.txt");
oout=new ObjectOutputStream(out);
oout.writeObject(obj);
oout.close();
}
}
else{
out=new FileOutputStream("obj.txt");
oout=new ObjectOutputStream(out);
oout.writeObject(obj);
oout.close();
}

in=new FileInputStream("obj.txt");
oin=new ObjectInputStream(in);
temp2=(SerializableTest)oin.readObject();
System.out.println(temp2.str);
}
catch(Exception e)
{
e.printStackTrace();
}
}
}