在 Java 中保存和加载到文件/从文件加载时出现问题

Question

我发布了一个类似的问题，它变得越来越混乱，这将更容易理解。Runner（） 中/注释掉/的部分。您取消注释，运行程序一次，检查控制台打印出来。然后/注释掉/再次，并再次运行程序，您会注意到子代码本 = {} 返回一个空白/null;这是我的问题，为什么返回 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();
    }
}

}

Answer 1

您尝试保存（和恢复）同一对象两次。试试这个笔记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();
        }
    }
}