对List和map等结构的常用转换操作基本上可以满足我们处理的绝大多数需求,但有时项目中对json有特殊的格式规定.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":"曹贵生","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":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}]

分析之后我们发现普通的方式都不好处理上面的json串.请看本文是如何处理的吧:

实体类:

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 + "]"; } }

注意这里定义了一个TableData实体类:

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; } }

测试类:
(仔细看将json转回为对象的实现,这里经过两次转化,第一次转回的结果是map不是我们所期望的对象,对map再次转为json后再转为对象,我引用的是Gson2.1的jar处理正常,好像使用Gson1.6的jar会报错,所以建议用最新版本)

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) { // 对象转为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("曹贵生"); 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("米老师"); teacher1.setTitle("教授"); Teacher teacher2 = new Teacher(); teacher2.setId(2); teacher2.setName("丁老师"); teacher2.setTitle("讲师"); 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); // 结果:[{"tableName":"students","tableData":[{"id":1,"name":"李坤","birthDay":"Jun 22, 2012 10:44:16 AM"},{"id":2,"name":"曹贵生","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":"米老师","title":"教授"},{"id":2,"name":"丁老师","title":"讲师"}]}] // 对象转为Json-->end // ///////////////////////////////////////////////////////////////////// // 将json转为数据-->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转为对象-->end } }

输出结果:

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

注册TypeAdapter及处理Enum类型

枚举类型给我们的程序带来了好处,如何用Gson来实现与Json的互转呢?请看本文.

本文重点掌握如何自己写一个TypeAdapter及注册TypeAdapter和处理Enum类型.

实体类:

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 + "]"; } }

自己写一个转换器实现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> { // 对象转为Json时调用,实现JsonSerializer<PackageState>接口 @Override public JsonElement serialize(PackageState state, Type arg1, JsonSerializationContext arg2) { return new JsonPrimitive(state.ordinal()); } // json转为对象时调用,实现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; } }

测试类:

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);// 这个 state是枚举值 String s = gson.toJson(item); System.out.println(s); System.out.println("--------------------------------"); PackageItem retItem = gson.fromJson(s, PackageItem.class); System.out.println(retItem); } }

输出结果(结果中已经将state的对应枚举类型转为了int类型):

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