如何使用GSON或Java中的其他JSON库反序列化列表？

Question

我可以在GAE上序列化我的servlet中的List,但我不能反序列化它.我究竟做错了什么？

这是我在GAE中的视频类,它是序列化的:

package legiontube;

import java.util.Date;

import javax.jdo.annotations.IdGeneratorStrategy;
import javax.jdo.annotations.IdentityType;
import javax.jdo.annotations.PersistenceCapable;
import javax.jdo.annotations.Persistent;
import javax.jdo.annotations.PrimaryKey;

@PersistenceCapable(identityType = IdentityType.APPLICATION)
public class Video {

    @PrimaryKey
    private String id;

    @Persistent
    private String titulo;

    @Persistent
    private String descricao;

    @Persistent
    private Date date;

    public Video(){};

 public Video(String id, String titulo, String descricao, Date date) {
  //super();
  this.id = id;
  this.titulo = titulo;
  this.descricao = descricao;
  this.date = date;
 }

 public String getId() {
  return id;
 }

 public void setId(String id) {
  this.id = id;
 }

 public String getTitulo() {
  return titulo;
 }

 public void setTitulo(String titulo) {
  this.titulo = titulo;
 }

 public String getDescricao() {
  return descricao;
 }

 public void setDescricao(String descricao) {
  this.descricao = descricao;
 }

 public Date getDate() {
  return date;
 }

 public void setDate(Date date) {
  this.date = date;
 }

}

这是我的其他应用程序中的类视频,我尝试反序列化:

package classes;

import java.util.Date;

public class Video {
 private String id;
 private String titulo;
 private String descricao;
 private Date date;

 public Video(String id, String titulo, String descricao, Date date) {
  //super();
  this.id = id;
  this.titulo = titulo;
  this.descricao = descricao;
  this.date = date;
 }

 public String getId() {
  return id;
 }
 public void setId(String id) {
  this.id = id;
 }
 public String getTitulo() {
  return titulo;
 }
 public void setTitulo(String titulo) {
  this.titulo = titulo;
 }
 public String getDescricao() {
  return descricao;
 }
 public void setDescricao(String descricao) {
  this.descricao = descricao;
 }
 public Date getDate() {
  return date;
 }
 public void setDate(Date date) {
  this.date = date;
 }

}

Answer 1

有了Gson,你只需要做一些事情:

List<Video> videos = gson.fromJson(json, new TypeToken<List<Video>>(){}.getType());

您可能还需要在Video要反序列化的类上提供无参数构造函数.

Answer 2

另一种方法是使用数组作为类型,例如:

Video[] videoArray = gson.fromJson(json, Video[].class);

这样你可以避免使用Type对象的所有麻烦,如果你真的需要一个列表,你总是可以将数组转换为列表,例如:

List<Video> videoList = Arrays.asList(videoArray);

恕我直言,这更具可读性.

Answer 3

试试这个单行

List<Video> videos = Arrays.asList(new Gson().fromJson(json, Video[].class));

参考:

1. 方法数组#asList
2. 构造函数Gson
3. 方法GSON#fromJson(源videos可以是类型的Arrays.asList,json或JsonElement)
4. 接口列表
5. JLS - 数组
6. JLS - 通用接口