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问题在Java中保存和加载到/从文件

更新时间：2023-12-01 22:54:04

Yout尝试保存（并恢复）相同的对象两次。尝试这个注释重要的部分 

  import java.io.FileInputStream ; 
 import java.io.FileOutputStream; 
 import java.io.IOException; 
 import java.io.InputStream; 
 import java.io.ObjectInputStream; 
 import java.io.ObjectOutputStream; 
 import java.io.OutputStream; 
 import java.io.Serializable; 
 import java.util.ArrayList; 
 import java.util.HashMap; 
 import java.util.LinkedList; 
 import java.util.List; 
 import java.util.Map; 

 public class Runner {

 Map< Integer，String> decodebook = new HashMap< Integer，String>（）; 
 //列表<整数> number = new LinkedList< Integer>（）; 
 Map< String，List< Integer>> codebook = new HashMap< String，List< Integer>>（）; 
 Map< String，List< Integer>> subcodebook = new HashMap< String，List< Integer>>（）; 
列表<整数> numbers = new LinkedList< Integer>（）; 
列表<整数> otherNumbers = new LinkedList< Integer>（）; 

 public static void main（String [] args）throws IOException {
 new Runner（）; 
} 

 public Runner（）throws IOException {

 numbers.add（6）; 
 numbers.add（156）; 
 numbers.add（363）; 
 numbers.add（336）; 
 numbers.add（26）; 
 numbers.add（61）; 

 otherNumbers.add（68）; 
 otherNumbers.add（78）; 
 otherNumbers.add（28）; 
 otherNumbers.add（668）; 
 otherNumbers.add（618）; 
 otherNumbers.add（686）; 
 otherNumbers.add（682）; 

 // ---------------------------------------- ----------------- 
 // 
 // imprtant part 
 // 
 // ------ -------------------------------------------------- ---- 
 subcodebook.put（tony，新的ArrayList（numbers.subList（0,2）））; 
 subcodebook.put（alf，new ArrayList（numbers.subList（3，5）））; 

 codebook.put（alf，数字）; 
 codebook.put（tony，otherNumbers）; 
 decodebook.put（7898，alf）; 
 decodebook.put（87576，tony）; 

 saveStuff（）; 
 System.out.println（codebook+ codebook）; 
 System.out.println（decodebook+ decodebook）; 
 System.out.println（subCodebook+子码本）; 
 loadBooks（）; 
 System.out.println（codebook+ codebook）; 
 System.out.println（decodebook+ decodebook）; 
 System.out.println（subCodebook+子码本）; 
} 

 public void loadBooks（）throws IOException {

 loadCodeBook（CodeBook）; 
 //System.out.println(codebook）; 

 loadsubCodeBook（subcodeBook）; 

 loadDeCodeBook（DecodeBook）; 
 // System.out.println（codebook）; 
 //System.out.println (decodebook）; 

} 

 public Map< String，List< Integer>> loadCodeBook（String filePath）
 throws IOException {
 HashMap< String，List< Integer>> codebook = null; 
 InputStream is = null; 
 try {
 is = new ObjectInputStream（new FileInputStream（filePath））; 
 codebook =（HashMap< String，List< Integer>）（（ObjectInputStream））
 .readObject（）; 
} catch（Exception ex）{
} finally {
 is.close（）; 
} 
 return this.codebook = codebook; 
} 

 public Map< String，List< Integer>> loadsubCodeBook（String filePath）
 throws IOException {
 HashMap< String，List< Integer>> subcodebook = null; 
 InputStream is = null; 
 try {
 is = new ObjectInputStream（new FileInputStream（filePath））; 
 subcodebook =（HashMap< String，List< Integer>）（（ObjectInputStream）is）
 .readObject（）; 
} catch（Exception ex）{
} finally {
 is.close（）; 
} 
 return this.subcodebook = subcodebook; 
} 

 public Map< Integer，String> loadDeCodeBook（String filePath）
 throws IOException {
 HashMap< Integer，String> decodebook = null; 
 InputStream is = null; 
 try {
 is = new ObjectInputStream（new FileInputStream（filePath））; 
 decodebook =（HashMap< Integer，String>）（（ObjectInputStream））
 .readObject（）; 
} catch（Exception ex）{
} finally {
 is.close（）; 
} 
 return this.decodebook = decodebook; 
} 

 public void saveStuff（）{
 try {
 saveCodeBook（codebook，CodeBook）; 

} catch（IOException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} 
 try {

 saveDecodeBook（decodebook，DecodeBook）; 
} catch（IOException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} 
 try {

 savesubCodeBook（subcodebook，subcodeBook）; 
} catch（IOException e）{
 // TODO自动生成的catch块
 e.printStackTrace（）; 
} 

} 

 public void saveCodeBook（Map< String，List< Integer>> obj，String filePath）
 throws IOException {
 OutputStream os = null; 
 try {
 os = new ObjectOutputStream（new FileOutputStream（filePath））; 

（（ObjectOutputStream）os）.writeObject（obj）; 
} catch（Exception ex）{
} finally {
 os.close（）; 
} 
} 

 public void savesubCodeBook（Map< String，List< Integer>> obj，String filePath）
 throws IOException {
 OutputStream os = null; 
 try {
 os = new ObjectOutputStream（new FileOutputStream（filePath））; 

（（ObjectOutputStream）os）.writeObject（obj）; 
} catch（Exception ex）{
} finally {
 os.close（）; 
} 
} 

 public void saveDecodeBook（Map< Integer，String> obj，String filePath）
 throws IOException {
 OutputStream os = null; 
 try {
 os = new ObjectOutputStream（new FileOutputStream（filePath））; 

（ObjectOutputStream）os）.writeObject（obj）; 
} catch（Exception ex）{
} finally {
 os.close（）; 
} 
} 

}


I have a similar question posted, it was getting messy and this will be much easier to follow. The part that is in the Runner() that is /commented out/. You un-comment this, run the program once, check you console print out. Then /comment it out/ again, and run the program a second time, you will notice that the subCodebook = {} is returning a blank/null; This is my question, why is this returning null. 

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class Runner {

Map<Integer, String> decodebook = new HashMap<Integer, String>();
// List<Integer> numbers = new LinkedList<Integer>();
Map<String, List<Integer>> codebook = new HashMap<String, List<Integer>>();
Map<String, List<Integer>> subcodebook = new HashMap<String, List<Integer>>();
List<Integer> numbers = new LinkedList<Integer>();
List<Integer> otherNumbers = new LinkedList<Integer>();

public static void main(String[] args) throws IOException {
    new Runner();
}

public Runner() throws IOException  {

    /*numbers.add(6);
    numbers.add(156);
    numbers.add(363);
    numbers.add(336);
    numbers.add(26);
    numbers.add(61);

    otherNumbers.add(68);
    otherNumbers.add(78);
    otherNumbers.add(28);
    otherNumbers.add(668);
    otherNumbers.add(618);
    otherNumbers.add(686);
    otherNumbers.add(682);

    subcodebook.put("tony", numbers.subList(0, 2));
    subcodebook.put("alf", numbers.subList(3, 5));


    codebook.put("alf", numbers);
    codebook.put("tony", otherNumbers);
    decodebook.put(7898, "alf");
    decodebook.put(87576, "tony");

     saveStuff();*/


     loadBooks();
     System.out.println(" codebook" + codebook);
     System.out.println(" decodebook" + decodebook);
     System.out.println(" subCodebook" + subcodebook);
}

public void loadBooks() throws IOException {

     loadCodeBook("CodeBook");
    //System.out.println(codebook);

     loadsubCodeBook("subCodeBook");


     loadDeCodeBook("DecodeBook");
    // System.out.println(codebook);
    //System.out.println(decodebook);

}

public Map<String, List<Integer>> loadCodeBook(String filePath)
        throws IOException {
    HashMap<String, List<Integer>> codebook = null;
    InputStream is = null;
    try {
        is = new ObjectInputStream(new FileInputStream(filePath));
        codebook = (HashMap<String, List<Integer>>) ((ObjectInputStream) is)
                .readObject();
    } catch (Exception ex) {
    } finally {
        is.close();
    }
    return this.codebook = codebook;
}
public Map<String, List<Integer>> loadsubCodeBook(String filePath)
        throws IOException {
    HashMap<String, List<Integer>> subcodebook = null;
    InputStream is = null;
    try {
        is = new ObjectInputStream(new FileInputStream(filePath));
        subcodebook = (HashMap<String, List<Integer>>) ((ObjectInputStream) is)
                .readObject();
    } catch (Exception ex) {
    } finally {
        is.close();
    }
    return this.subcodebook = subcodebook;
}


public Map<Integer, String> loadDeCodeBook(String filePath)
        throws IOException {
    HashMap<Integer, String> decodebook = null;
    InputStream is = null;
    try {
        is = new ObjectInputStream(new FileInputStream(filePath));
        decodebook = (HashMap<Integer, String>) ((ObjectInputStream) is)
                .readObject();
    } catch (Exception ex) {
    } finally {
        is.close();
    }
    return this.decodebook = decodebook;
}

public void saveStuff() {
    try {
        saveCodeBook(codebook, "CodeBook");

    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {

        saveDecodeBook(decodebook, "DecodeBook");
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
    try {

        savesubCodeBook(subcodebook, "subcodeBook");
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }

}

public void saveCodeBook(Map<String, List<Integer>> obj, String filePath)
        throws IOException {
    OutputStream os = null;
    try {
        os = new ObjectOutputStream(new FileOutputStream(filePath));

        ((ObjectOutputStream) os).writeObject(obj);
    } catch (Exception ex) {
    } finally {
        os.close();
    }
}

public void savesubCodeBook(Map<String, List<Integer>> obj, String filePath)
        throws IOException {
    OutputStream os = null;
    try {
        os = new ObjectOutputStream(new FileOutputStream(filePath));

        ((ObjectOutputStream) os).writeObject(obj);
    } catch (Exception ex) {
    } finally {
        os.close();
    }
}

public void saveDecodeBook(Map<Integer, String> obj, String filePath)
        throws IOException {
    OutputStream os = null;
    try {
        os = new ObjectOutputStream(new FileOutputStream(filePath));

        ((ObjectOutputStream) os).writeObject(obj);
    } catch (Exception ex) {
    } finally {
        os.close();
    }
}

}

Yout try to save (and restore) the same object twice. Try this an note the important part

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.io.OutputStream;
import java.io.Serializable;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class Runner {

    Map<Integer, String> decodebook = new HashMap<Integer, String>();
// List<Integer> numbers = new LinkedList<Integer>();
    Map<String, List<Integer>> codebook = new HashMap<String, List<Integer>>();
    Map<String, List<Integer>> subcodebook = new HashMap<String, List<Integer>>();
    List<Integer> numbers = new LinkedList<Integer>();
    List<Integer> otherNumbers = new LinkedList<Integer>();

    public static void main(String[] args) throws IOException {
        new Runner();
    }

    public Runner() throws IOException {

        numbers.add(6);
        numbers.add(156);
        numbers.add(363);
        numbers.add(336);
        numbers.add(26);
        numbers.add(61);

        otherNumbers.add(68);
        otherNumbers.add(78);
        otherNumbers.add(28);
        otherNumbers.add(668);
        otherNumbers.add(618);
        otherNumbers.add(686);
        otherNumbers.add(682);

        // ---------------------------------------------------------
        //
        //  the imprtant part
        // 
        // ------------------------------------------------------------
        subcodebook.put("tony", new ArrayList(numbers.subList(0, 2)));
        subcodebook.put("alf", new ArrayList(numbers.subList(3, 5)));

        codebook.put("alf", numbers);
        codebook.put("tony", otherNumbers);
        decodebook.put(7898, "alf");
        decodebook.put(87576, "tony");

        saveStuff();
        System.out.println(" codebook" + codebook);
        System.out.println(" decodebook" + decodebook);
        System.out.println(" subCodebook" + subcodebook);
        loadBooks();
        System.out.println(" codebook" + codebook);
        System.out.println(" decodebook" + decodebook);
        System.out.println(" subCodebook" + subcodebook);
    }

    public void loadBooks() throws IOException {

        loadCodeBook("CodeBook");
        //System.out.println(codebook);

        loadsubCodeBook("subcodeBook");

        loadDeCodeBook("DecodeBook");
        // System.out.println(codebook);
        //System.out.println(decodebook);

    }

    public Map<String, List<Integer>> loadCodeBook(String filePath)
            throws IOException {
        HashMap<String, List<Integer>> codebook = null;
        InputStream is = null;
        try {
            is = new ObjectInputStream(new FileInputStream(filePath));
            codebook = (HashMap<String, List<Integer>>) ((ObjectInputStream) is)
                    .readObject();
        } catch (Exception ex) {
        } finally {
            is.close();
        }
        return this.codebook = codebook;
    }

    public Map<String, List<Integer>> loadsubCodeBook(String filePath)
            throws IOException {
        HashMap<String, List<Integer>> subcodebook = null;
        InputStream is = null;
        try {
            is = new ObjectInputStream(new FileInputStream(filePath));
            subcodebook = (HashMap<String, List<Integer>>) ((ObjectInputStream) is)
                    .readObject();
        } catch (Exception ex) {
        } finally {
            is.close();
        }
        return this.subcodebook = subcodebook;
    }

    public Map<Integer, String> loadDeCodeBook(String filePath)
            throws IOException {
        HashMap<Integer, String> decodebook = null;
        InputStream is = null;
        try {
            is = new ObjectInputStream(new FileInputStream(filePath));
            decodebook = (HashMap<Integer, String>) ((ObjectInputStream) is)
                    .readObject();
        } catch (Exception ex) {
        } finally {
            is.close();
        }
        return this.decodebook = decodebook;
    }

    public void saveStuff() {
        try {
            saveCodeBook(codebook, "CodeBook");

        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {

            saveDecodeBook(decodebook, "DecodeBook");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        try {

            savesubCodeBook(subcodebook, "subcodeBook");
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

    }

    public void saveCodeBook(Map<String, List<Integer>> obj, String filePath)
            throws IOException {
        OutputStream os = null;
        try {
            os = new ObjectOutputStream(new FileOutputStream(filePath));

            ((ObjectOutputStream) os).writeObject(obj);
        } catch (Exception ex) {
        } finally {
            os.close();
        }
    }

    public void savesubCodeBook(Map<String, List<Integer>> obj, String filePath)
            throws IOException {
        OutputStream os = null;
        try {
            os = new ObjectOutputStream(new FileOutputStream(filePath));

            ((ObjectOutputStream) os).writeObject(obj);
        } catch (Exception ex) {
        } finally {
            os.close();
        }
    }

    public void saveDecodeBook(Map<Integer, String> obj, String filePath)
            throws IOException {
        OutputStream os = null;
        try {
            os = new ObjectOutputStream(new FileOutputStream(filePath));

            ((ObjectOutputStream) os).writeObject(obj);
        } catch (Exception ex) {
        } finally {
            os.close();
        }
    }

}

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