相当于Java中的python的shelve模块

Question

Java中有没有等同于python的shelve模块的模块？我需要它来实现像字典一样的分类数据访问。类字典分类数据访问是将Python对象保存为持久的、易于访问的数据库格式的强大方法。我需要一些相同的东西，但在Java中。

Answer 1

我也需要这个，所以我写了一个。有点晚了，但也许会有帮助。

它没有实现close()方法，而只是使用sync()，因为它只在实际写入文件时保持文件打开。

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.HashMap;

public class Shelf extends HashMap<String, Object> {
    private static final long serialVersionUID = 7127639025670585367L;
    private final File file;

    public static Shelf open(File file) {
    Shelf shelf = null;
    try {
        if (file.exists()) {
        final FileInputStream fis = new FileInputStream(file);
        ObjectInputStream ois = new ObjectInputStream(fis);
        shelf = (Shelf) ois.readObject();
        ois.close();
        fis.close();
        } else {
        shelf = new Shelf(file);
        shelf.sync();
        }
    } catch (Exception e) {
        // TODO: handle errors
    }
    return shelf;
    }

    // Shelf objects can only be created or opened by the Shelf.open method
    private Shelf(File file) {
    this.file = file;
    sync();
    }

    public void sync() {
    try {
        final FileOutputStream fos = new FileOutputStream(file);
        ObjectOutputStream oos = new ObjectOutputStream(fos);
        oos.writeObject(this);
        oos.close();
        fos.close();
    } catch (Exception e) {
        // TODO: handle errors
    }
    }

    // Simple Test Case
    public static void main(String[] args) {
    Shelf shelf = Shelf.open(new File("test.obj"));
    if (shelf.containsKey("test")) {
        System.out.println(shelf.get("test"));
    } else {
        System.out.println("Creating test string.  Run the program again.");
        shelf.put("test", "Hello Shelf!");
        shelf.sync();
    }
    }
}

Answer 2

您可以使用像Jackson这样的序列化库，它将POJO序列化为JSON。

来自tutorial的示例

Jackson的org.codehaus.jackson.map.ObjectMapper用于将

数据映射到普通的旧org.codehaus.jackson.map.ObjectMapper对象(“POJO”)。例如，给定JSON数据

{
  "name" : { "first" : "Joe", "last" : "Sixpack" },
  "gender" : "MALE",
  "verified" : false,
  "userImage" : "Rm9vYmFyIQ=="
}

需要两行Java代码才能将其转换为User实例：

ObjectMapper mapper = new ObjectMapper(); // can reuse, share globally
User user = mapper.readValue(new File("user.json"), User.class);

User类如下所示的

(来自Tatu博客上的entry )：

public class User {
    public enum Gender { MALE, FEMALE };

    public static class Name {
      private String _first, _last;

      public String getFirst() { return _first; }
      public String getLast() { return _last; }

      public void setFirst(String s) { _first = s; }
      public void setLast(String s) { _last = s; }
    }

    private Gender _gender;
    private Name _name;
    private boolean _isVerified;
    private byte[] _userImage;

    public Name getName() { return _name; }
    public boolean isVerified() { return _isVerified; }
    public Gender getGender() { return _gender; }
    public byte[] getUserImage() { return _userImage; }

    public void setName(Name n) { _name = n; }
    public void setVerified(boolean b) { _isVerified = b; }
    public void setGender(Gender g) { _gender = g; }
    public void setUserImage(byte[] b) { _userImage = b; }
}