使用GSON庫轉(zhuǎn)換Java對象為JSON對象的進(jìn)階實例詳解

更新時間：2016年06月22日 11:14:37 作者：李坤

這篇文章主要介紹了使用GSON庫轉(zhuǎn)換Java對象為JSON對象的進(jìn)階實例詳解,包括注冊TypeAdapter及處理Enum類型等實際運用中可能遇到的一些復(fù)雜問題,需要的朋友可以參考下

對List和map等結(jié)構(gòu)的常用轉(zhuǎn)換操作基本上可以滿足我們處理的絕大多數(shù)需求,但有時項目中對json有特殊的格式規(guī)定.比如下面的json串解析:

[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":2,"name":"曹貴生","birthDay":"Jun 22, 2012 9:54:49 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 9:54:49 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老師","title":"教授"},{"id":2,"name":"丁老師","title":"講師"}]}]

分析之后我們發(fā)現(xiàn)普通的方式都不好處理上面的json串.請看本文是如何處理的吧:

實體類:

import java.util.Date; 
 
public class Student { 
  private int id; 
  private String name; 
  private Date birthDay; 
 
  public int getId() { 
    return id; 
  } 
 
  public void setId(int id) { 
    this.id = id; 
  } 
 
  public String getName() { 
    return name; 
  } 
 
  public void setName(String name) { 
    this.name = name; 
  } 
 
  public Date getBirthDay() { 
    return birthDay; 
  } 
 
  public void setBirthDay(Date birthDay) { 
    this.birthDay = birthDay; 
  } 
 
  @Override 
  public String toString() { 
    return "Student [birthDay=" + birthDay + ", id=" + id + ", name=" 
        + name + "]"; 
  } 
 
} 

public class Teacher { 
  private int id; 
 
  private String name; 
 
  private String title; 
 
  public int getId() { 
    return id; 
  } 
 
  public void setId(int id) { 
    this.id = id; 
  } 
 
  public String getName() { 
    return name; 
  } 
 
  public void setName(String name) { 
    this.name = name; 
  } 
 
  public String getTitle() { 
    return title; 
  } 
 
  public void setTitle(String title) { 
    this.title = title; 
  } 
 
  @Override 
  public String toString() { 
    return "Teacher [id=" + id + ", name=" + name + ", title=" + title 
        + "]"; 
  } 
 
}

注意這里定義了一個TableData實體類:

import java.util.List; 
 
public class TableData { 
 
  private String tableName; 
 
  private List tableData; 
 
  public String getTableName() { 
    return tableName; 
  } 
 
  public void setTableName(String tableName) { 
    this.tableName = tableName; 
  } 
 
  public List getTableData() { 
    return tableData; 
  } 
 
  public void setTableData(List tableData) { 
    this.tableData = tableData; 
  } 
}

測試類:
(仔細(xì)看將json轉(zhuǎn)回為對象的實現(xiàn),這里經(jīng)過兩次轉(zhuǎn)化,第一次轉(zhuǎn)回的結(jié)果是map不是我們所期望的對象,對map再次轉(zhuǎn)為json后再轉(zhuǎn)為對象,我引用的是Gson2.1的jar處理正常,好像使用Gson1.6的jar會報錯,所以建議用最新版本)

import java.util.ArrayList; 
import java.util.Date; 
import java.util.List; 
 
import com.google.gson.Gson; 
import com.google.gson.reflect.TypeToken; 
 
public class GsonTest5 { 
 
  /** 
   * @param args 
   */ 
  public static void main(String[] args) { 
    // 對象轉(zhuǎn)為Json-->start 
    Student student1 = new Student(); 
    student1.setId(1); 
    student1.setName("李坤"); 
    student1.setBirthDay(new Date()); 
 
    Student student2 = new Student(); 
    student2.setId(2); 
    student2.setName("曹貴生"); 
    student2.setBirthDay(new Date()); 
 
    Student student3 = new Student(); 
    student3.setId(3); 
    student3.setName("柳波"); 
    student3.setBirthDay(new Date()); 
 
    List<Student> stulist = new ArrayList<Student>(); 
    stulist.add(student1); 
    stulist.add(student2); 
    stulist.add(student3); 
 
    Teacher teacher1 = new Teacher(); 
    teacher1.setId(1); 
    teacher1.setName("米老師"); 
    teacher1.setTitle("教授"); 
 
    Teacher teacher2 = new Teacher(); 
    teacher2.setId(2); 
    teacher2.setName("丁老師"); 
    teacher2.setTitle("講師"); 
    List<Teacher> teacherList = new ArrayList<Teacher>(); 
    teacherList.add(teacher1); 
    teacherList.add(teacher2); 
 
    TableData td1 = new TableData(); 
    td1.setTableName("students"); 
    td1.setTableData(stulist); 
 
    TableData td2 = new TableData(); 
    td2.setTableName("teachers"); 
    td2.setTableData(teacherList); 
 
    List<TableData> tdList = new ArrayList<TableData>(); 
    tdList.add(td1); 
    tdList.add(td2); 
    Gson gson = new Gson(); 
    String s = gson.toJson(tdList); 
 
    System.out.println(s); 
    // 結(jié)果:[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":2,"name":"曹貴生","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:44:16 AM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老師","title":"教授"},{"id":2,"name":"丁老師","title":"講師"}]}] 
    // 對象轉(zhuǎn)為Json-->end 
 
    // ///////////////////////////////////////////////////////////////////// 
 
    // 將json轉(zhuǎn)為數(shù)據(jù)-->start 
    List<TableData> tableDatas2 = gson.fromJson(s, 
        new TypeToken<List<TableData>>() { 
        }.getType()); 
    for (int i = 0; i < tableDatas2.size(); i++) { 
      TableData entityData = tableDatas2.get(i); 
      String tableName = entityData.getTableName(); 
      List tableData = entityData.getTableData(); 
      String s2 = gson.toJson(tableData); 
      // System.out.println(s2); 
      // System.out.println(entityData.getData()); 
      if (tableName.equals("students")) { 
        System.out.println("students"); 
        List<Student> retStuList = gson.fromJson(s2, 
            new TypeToken<List<Student>>() { 
            }.getType()); 
        for (int j = 0; j < retStuList.size(); j++) { 
          System.out.println(retStuList.get(j)); 
        } 
 
      } else if (tableName.equals("teachers")) { 
        System.out.println("teachers"); 
        List<Teacher> retTchrList = gson.fromJson(s2, 
            new TypeToken<List<Teacher>>() { 
            }.getType()); 
        for (int j = 0; j < retTchrList.size(); j++) { 
          System.out.println(retTchrList.get(j)); 
        } 
      } 
    } 
 
    // Json轉(zhuǎn)為對象-->end 
  } 
}

輸出結(jié)果:

[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":2,"name":"曹貴生","birthDay":"Jun 22, 2012 10:04:12 PM"},{"id":3,"name":"柳波","birthDay":"Jun 22, 2012 10:04:12 PM"}]},{"tableName":"teachers","tableData":[{"id":1,"name":"米老師","title":"教授"},{"id":2,"name":"丁老師","title":"講師"}]}] 
students 
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=1, name=李坤] 
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=2, name=曹貴生] 
Student [birthDay=Fri Jun 22 22:04:12 CST 2012, id=3, name=柳波] 
teachers 
Teacher [id=1, name=米老師, title=教授] 
Teacher [id=2, name=丁老師, title=講師]

注冊TypeAdapter及處理Enum類型

枚舉類型給我們的程序帶來了好處,如何用Gson來實現(xiàn)與Json的互轉(zhuǎn)呢?請看本文.

本文重點掌握如何自己寫一個TypeAdapter及注冊TypeAdapter和處理Enum類型.

實體類:

public enum PackageState { 
  PLAY, UPDATE, UPDATING, DOWNLOAD, DOWNLOADING, 
} 

public class PackageItem { 
  private String name; 
  private PackageState state; 
  private String size; 
 
  public String getName() { 
    return name; 
  } 
 
  public void setName(String name) { 
    this.name = name; 
  } 
 
  public PackageState getState() { 
    return state; 
  } 
 
  public void setState(PackageState state) { 
    this.state = state; 
  } 
 
  public String getSize() { 
    return size; 
  } 
 
  public void setSize(String size) { 
    this.size = size; 
  } 
 
  @Override 
  public String toString() { 
    return "PackageItem [name=" + name + ", size=" + size + ", state=" 
        + state + "]"; 
  } 
}

自己寫一個轉(zhuǎn)換器實現(xiàn)JsonSerializer<T>接口和jsonDeserializer<T>接口:

import java.lang.reflect.Type; 
 
import com.google.gson.JsonDeserializationContext; 
import com.google.gson.JsonDeserializer; 
import com.google.gson.JsonElement; 
import com.google.gson.JsonParseException; 
import com.google.gson.JsonPrimitive; 
import com.google.gson.JsonSerializationContext; 
import com.google.gson.JsonSerializer; 
 
public class EnumSerializer implements JsonSerializer<PackageState>, 
    JsonDeserializer<PackageState> { 
 
  // 對象轉(zhuǎn)為Json時調(diào)用,實現(xiàn)JsonSerializer<PackageState>接口 
  @Override 
  public JsonElement serialize(PackageState state, Type arg1, 
      JsonSerializationContext arg2) { 
    return new JsonPrimitive(state.ordinal()); 
  } 
 
  // json轉(zhuǎn)為對象時調(diào)用,實現(xiàn)JsonDeserializer<PackageState>接口 
  @Override 
  public PackageState deserialize(JsonElement json, Type typeOfT, 
      JsonDeserializationContext context) throws JsonParseException { 
    if (json.getAsInt() < PackageState.values().length) 
      return PackageState.values()[json.getAsInt()]; 
    return null; 
  } 
 
}

測試類:

import com.google.gson.Gson; 
import com.google.gson.GsonBuilder; 
 
public class GsonTest6 { 
 
  public static void main(String[] args) { 
    GsonBuilder gsonBuilder = new GsonBuilder(); 
    gsonBuilder.registerTypeAdapter(PackageState.class, 
        new EnumSerializer()); 
    Gson gson = gsonBuilder.create(); 
    PackageItem item = new PackageItem(); 
    item.setName("item_name"); 
    item.setSize("500M"); 
    item.setState(PackageState.UPDATING);// 這個 state是枚舉值 
 
    String s = gson.toJson(item); 
    System.out.println(s); 
 
    System.out.println("--------------------------------"); 
 
    PackageItem retItem = gson.fromJson(s, PackageItem.class); 
    System.out.println(retItem); 
  } 
}

輸出結(jié)果(結(jié)果中已經(jīng)將state的對應(yīng)枚舉類型轉(zhuǎn)為了int類型):

{"name":"item_name","state":2,"size":"500M"} 
-------------------------------- 
PackageItem [name=item_name, size=500M, state=UPDATING]

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