Gson 解析教程

甘甘灰 2018-08-03

展开全文

Gson 是google解析Json的一个开源框架,同类的框架fastJson,JackJson等等

本人fastJson用了两年，也是从去年才开始接触Gson,希望下面的总结会对博友有用,至于Gson与FastJson的对比,其实半斤八两的问题,不再赘述

第一步:在AS下面创建java工程并添加gson依赖

compile 'com.google.code.gson:gson:2.6.2'

Gson的实例化方式:

1:Gson gson=newGson();

2:通过GsonBuilder 可以配置多种选项

 gson = new GsonBuilder()
                    .setLenient()// json宽松
                    .enableComplexMapKeySerialization()//支持Map的key为复杂对象的形式
                    .serializeNulls() //智能null
                    .setPrettyPrinting()// 调教格式
                    .disableHtmlEscaping() //默认是GSON把HTML 转义的
                    .create();

Gson的基本用法:

JavaBean转换Json字符串

gson提供 publicString toJson(Object src) 方法可以将对象转换成jsonStr

package com.xuan.gson;
import com.google.gson.Gson;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 10:39
 */
public class GsonTest1 {
    public static class Student {
        private String name;
        private int age;
        //省略setter getter equals
    }
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static void main(String[] args) throws Exception {
        Gson gson = new Gson();
        Student student = new Student();
        student.setName("xuanyouwu");
        student.setAge(26);
        String jsonStr = gson.toJson(student);
        log("---->javabean convert jsonStr:" + jsonStr);
    }
}

运行结果:

---->javabean convert jsonStr:{"name":"xuanyouwu","age":26}

List Map转Json字符串

package com.xuan.gson;
import com.google.gson.Gson;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 10:39
 */
public class GsonTest1 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static void main(String[] args) throws Exception {
        Gson gson = new Gson();
        List<String> list = Arrays.asList("1", "a", "3", "rt", "5");
        log("---->list convert jsonStr:" + gson.toJson(list));
        Map<String, Object> content = new HashMap<String, Object>();
        content.put("name", "xuanyouwu");
        content.put("age", "26");
        log("---->map convert jsonStr:" + gson.toJson(content));
    }
}

运行结果:

---->list convert jsonStr:["1","a","3","rt","5"]
---->map convert jsonStr:{"name":"xuanyouwu","age":"26"}

Json字符串转JavaBean

        String studentJsonStr="{\"name\":\"xuanyouwu\",\"age\":26}";
        Student student1 = gson.fromJson(studentJsonStr, Student.class);
        log("------->json convert JavaBean:"+student1);

运行结果:

------->json convert JavaBean:Student{name='xuanyouwu', age=26}

Json字符串转List

        String listJsonStr="[\"1\",\"a\",\"3\",\"rt\",\"5\"]";

        Type type = new TypeToken<ArrayList<String>>() {
        }.getType();
        ArrayList<String> sList=gson.fromJson(listJsonStr, type);
        log("------->json convert List:"+sList);

    运行结果:

        ------->json convert List:[1, a, 3, rt, 5]

</pre><pre code_snippet_id="1687762" snippet_file_name="blog_20160518_11_939636" name="code" class="java">  Gson封装的类型体系

    Gson里面有一个非常有意思的抽象基类JsonElement,他的继承体系:

    <img src="https://img-blog.csdn.net/20160518135136864?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center" alt="" />

 JsonObject等同于org的JSONObject,JsonArray也类似,

   JsonNull 其实就是null 字段

     JsonNull jsonNull=new JsonNull();//构造方法过时，推荐INSTANCE

      JsonNull jsonNull=JsonNull.INSTANCE;
        log("-----"+jsonNull);

   运行结果:

      -----null

JsonPrimitive非常有意思,我们知道如果json转换成字符串可能包含引号的转义，但是通过JsonPrimative我们可以获得为转义的字符串，看实例：

package com.xuan.gson;
import com.google.gson.JsonNull;
import com.google.gson.JsonPrimitive;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest2 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static void main(String[] args) throws Exception {
        String studentJsonStr="{\"name\":\"xuanyouwu\",\"age\":26}";
        log("------>studentJsonStr:"+studentJsonStr);
        JsonPrimitive jsonPrimitive=new JsonPrimitive(studentJsonStr);
        log("------>jsonPrimitive:"+jsonPrimitive);
        log("------>jsonPrimitive:"+jsonPrimitive.toString());
        log("------>jsonPrimitive:"+jsonPrimitive.getAsString());
        JsonPrimitive jsonPrimitive2=new JsonPrimitive("this is String");
        log("------>jsonPrimitive2:"+jsonPrimitive2);
        log("------>jsonPrimitive2:"+jsonPrimitive2.toString());
        log("------>jsonPrimitive2:"+jsonPrimitive2.getAsString());
    }
}

运行结果:

------>studentJsonStr:{"name":"xuanyouwu","age":26}
------>jsonPrimitive:"{\"name\":\"xuanyouwu\",\"age\":26}"
------>jsonPrimitive:"{\"name\":\"xuanyouwu\",\"age\":26}"
------>jsonPrimitive:{"name":"xuanyouwu","age":26}
------>jsonPrimitive2:"this is String"
------>jsonPrimitive2:"this is String"
------>jsonPrimitive2:this is String

创建JsonObject

通过addPropert(key,value)可以向jsonObject中添加字段跟hashMap类似

        JsonObject jsonObject=new JsonObject();
        jsonObject.addProperty("name","xuanyouwu");
        jsonObject.addProperty("age",26);
        log("------>create jsonObject:"+jsonObject);

运行结果:

------>create jsonObject:{"name":"xuanyouwu","age":26}

创建JsonArray

     JsonArray jsonElements=new JsonArray();
        jsonElements.add("a");
        jsonElements.add("b");
        jsonElements.add("c");
        jsonElements.add("d");
        log("------>create jsonArray:"+jsonElements);

运行结果:

------>create jsonArray:["a","b","c","d"]

JsonObject 嵌套数组或者说嵌套JsonArray

通过JsonObject的add(key,JsonElement)可以为jsonObject 添加一个数组的字段

        JsonObject jsonObject2=new JsonObject();
        jsonObject2.addProperty("name","xuanyouwu");
        jsonObject2.addProperty("age",26);
        JsonArray jsonElements2=new JsonArray();
        jsonElements2.add("骑车");
        jsonElements2.add("打游戏");
        jsonElements2.add("看电视");
        jsonObject2.add("hobby",jsonElements2);
        log("------>create jsonObject inner JsonArray:"+jsonObject2);

运行结果:

------>create jsonObject inner JsonArray:{"name":"xuanyouwu","age":26,"hobby":["骑车","打游戏","看电视"]}

Gson注解

在Gson中有五类注解

重命名注解:SerializedName

作用:转换关键字key,json转换成JavaBean时,json字段的key 默认必须和我们声明类的字段名称一样,当服务器端返回了关键字怎么办，比如key 为new switch这样,我们在声明类的时候不能写这样的字段,可能你想服务器端改动，他可能要改数据库，但是我告诉你，做服务端的大部分不愿意改动他的json,是很自私的!这时候重命名注解都排上用场了第二种场景:服务器端返回的json 的key 简直太丑，或者太长,你想简化,my_parent_name,可以简化成mpn 比较优雅简介

实例:

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.annotations.SerializedName;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest3 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        public int age;
        @SerializedName("new")
        public int isnew;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", isnew=" + isnew +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\n" +
                "    \"age\": 26,\n" +
                "    \"name\": \"zhangsan\",\n" +
                "    \"new\": 1\n" +
                "}";
        Gson gson = new Gson();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>user:" + user);
    }
}

运行结果: ------>user:User{name='zhangsan', age=26, isnew=1}

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.annotations.SerializedName;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest3 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User2 {
        public String name;
        public int age;
        @SerializedName("my_parent_name")
        public String pn;
        @Override
        public String toString() {
            return "User2{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", pn='" + pn + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer2="{\n" +
                "    \"age\": 26,\n" +
                "    \"my_parent_name\": \"zhangsanf\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        Gson gson2 = new Gson();
        User2 user2 = gson2.fromJson(jsonFromServer2, User2.class);
        log("------>user2:" + user2);
    }
}

运行结果: ------>user2:User2{name='zhangsan', age=26, pn='zhangsanf'}

作用2:结合alternate 提供多种备用字段key来解析,@SerializedName(value ="desc",alternate = {"other","note"}) 如果json中有other就会解析成desc 如果有note也会解析成desc,注意1:value中的值不能出现在alternate中,注意2:alternate的备选字段会后面的替换前面的

实例：

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.annotations.SerializedName;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest4 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        public int age;
        @SerializedName(value = "desc",alternate = {"other","note"})
        public String desc;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    ", desc='" + desc + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\n" +
                "    \"age\": 26,\n" +
                "    \"other\": \"成都人\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        Gson gson = new Gson();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>user:" + user);
        String jsonFromServer2 = "{\n" +
                "    \"age\": 26,\n" +
                "    \"note\": \"成都人\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        User user2 = gson.fromJson(jsonFromServer2, User.class);
        log("------>user:" + user2);
        //包括desc 与note note在desc之后
        String jsonFromServer3="{\n" +
                "    \"age\": 26,\n" +
                "    \"desc\": \"desc成都人\",\n" +
                "    \"name\": \"zhangsan\",\n" +
                "    \"note\": \"note成都人\"\n" +
                "}";
        User user3 = gson.fromJson(jsonFromServer3, User.class);
        log("------>user:" + user3);
        //包括desc 与note note在desc之前
        String jsonFromServer4="{\n" +
                "    \"age\": 26,\n" +
                "    \"note\": \"note成都人\",\n" +
                "    \"name\": \"zhangsan\",\n" +
                "    \"desc\": \"desc成都人\"\n" +
                "}";
        User user4 = gson.fromJson(jsonFromServer4, User.class);
        log("------>user:" + user4);
    }
}

运行结果:

------>user:User{name='zhangsan', age=26, desc='成都人'}
------>user:User{name='zhangsan', age=26, desc='成都人'}
------>user:User{name='zhangsan', age=26, desc='note成都人'}
------>user:User{name='zhangsan', age=26, desc='desc成都人'}

Gson @Expose过滤注解

源码:默认既可以序列化又可以反序列化

@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
public @interface Expose {
  public boolean serialize() default true;
  public boolean deserialize() default true;
}

</pre><pre code_snippet_id="1687762" snippet_file_name="blog_20160518_25_4965554" name="code" class="java">可以排除不需要序列化的字段,需要配合GsonBuilder使用

<pre style="font-family: 宋体; font-size: 9pt; background-color: rgb(255, 255, 255);"><pre name="code" class="java"> Gson gson = new GsonBuilder()
                .excludeFieldsWithoutExposeAnnotation()
                .create();

  不添加@Expose注解的字段将不会解析:

   分为以下几种情况:

    1:不添加@Expose注解等同于@Expose(deserialize = false,serialize = false) 不做任何解析

    2:@Expose(deserialize = true,serialize = false) 只解析用用，也就是反序列化可以，序列化不可以

    3:@Expose(deserialize = false,serialize = true) 序列化可以，反序列化不行

    4:@Expose(deserialize = true,serialize = true) 既可以序列化，也可以反序列化

    实例:将分别演示这四种情况

  不添加@Expose注解:等同于@Expose(deserialize = false,serialize = false)

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest5 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .excludeFieldsWithoutExposeAnnotation()
                .create();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化:" + user);
        User user1 = new User();
        user1.name = "zhangsan2";
        String userStr = gson.toJson(user1);
        log("------>序列化:" + userStr);
    }
}

运行结果:

------>反序列化:User{name='null'}
------>序列化:{}

  添加@Expose注解

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest5 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        @Expose //等同于 @Expose(deserialize = true,serialize = true)
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .excludeFieldsWithoutExposeAnnotation()
                .create();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化:" + user);
        User user1 = new User();
        user1.name = "zhangsan2";
        String userStr = gson.toJson(user1);
        log("------>序列化:" + userStr);
    }
}

运行结果:

------>反序列化:User{name='zhangsan'}
------>序列化:{"name":"zhangsan2"}

@Expose注解只序列化

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest5 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        @Expose(deserialize = false,serialize = true)
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .excludeFieldsWithoutExposeAnnotation()
                .create();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化:" + user);
        User user1 = new User();
        user1.name = "zhangsan2";
        String userStr = gson.toJson(user1);
        log("------>序列化:" + userStr);
    }
}

运行结果:

------>反序列化:User{name='null'}------>序列化:{"name":"zhangsan2"}

@Expose 只反序列化

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Expose;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest5 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        @Expose(deserialize = true, serialize = false)
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .excludeFieldsWithoutExposeAnnotation()
                .create();
        User user = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化:" + user);
        User user1 = new User();
        user1.name = "zhangsan2";
        String userStr = gson.toJson(user1);
        log("------>序列化:" + userStr);
    }
}

运行结果:

------>反序列化:User{name='zhangsan'}
------>序列化:{}

@Since(float v)注解版本控制

结合GsonBuilder.setVersion(n)使用当n>=v时才会序列化解析

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Since;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest6 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        @Since(2)
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .setVersion(1)//版本为1
                .create();
        User user1 = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=1:" + user1);
        User user1_1 = new User();
        user1_1.name = "zhangsan2";
        String userStr = gson.toJson(user1_1);
        log("------>序列化v=1:" + userStr);
        Gson gson2 = new GsonBuilder()
                .setVersion(2)//版本为2
                .create();
        User user2 = gson2.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=2:" + user2);
        User user2_1 = new User();
        user2_1.name = "zhangsan2";
        String userStr2_1 = gson2.toJson(user2_1);
        log("------>序列化v=2:" + userStr2_1);
        Gson gson3 = new GsonBuilder()
                .setVersion(3)//版本为3
                .create();
        User user3 = gson3.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=3:" + user3);
        User user3_1 = new User();
        user3_1.name = "zhangsan2";
        String userStr3_1 = gson3.toJson(user3_1);
        log("------>序列化v=3:" + userStr3_1);
    }
}

运行结果:

------>反序列化v=1:User{name='null'}
------>序列化v=1:{}
------>反序列化v=2:User{name='zhangsan'}
------>序列化v=2:{"name":"zhangsan2"}
------>反序列化v=3:User{name='zhangsan'}
------>序列化v=3:{"name":"zhangsan2"}

@Util(float v)注解版本控制

当gson的setVersion(n) n<v 才解析

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.annotations.Until;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest6 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        @Until(2)
        public String name;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        String jsonFromServer = "{\"name\": \"zhangsan\"}";
        Gson gson = new GsonBuilder()
                .setVersion(1)//版本为1
                .create();
        User user1 = gson.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=1:" + user1);
        User user1_1 = new User();
        user1_1.name = "zhangsan2";
        String userStr = gson.toJson(user1_1);
        log("------>序列化v=1:" + userStr);
        Gson gson2 = new GsonBuilder()
                .setVersion(2)//版本为2
                .create();
        User user2 = gson2.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=2:" + user2);
        User user2_1 = new User();
        user2_1.name = "zhangsan2";
        String userStr2_1 = gson2.toJson(user2_1);
        log("------>序列化v=2:" + userStr2_1);
        Gson gson3 = new GsonBuilder()
                .setVersion(3)//版本为3
                .create();
        User user3 = gson3.fromJson(jsonFromServer, User.class);
        log("------>反序列化v=3:" + user3);
        User user3_1 = new User();
        user3_1.name = "zhangsan2";
        String userStr3_1 = gson3.toJson(user3_1);
        log("------>序列化v=3:" + userStr3_1);
    }
}

运行结果:

------>反序列化v=1:User{name='zhangsan'}
------>序列化v=1:{"name":"zhangsan2"}
------>反序列化v=2:User{name='null'}
------>序列化v=2:{}
------>反序列化v=3:User{name='null'}
------>序列化v=3:{}

Gson 高级用法

相信看过retrofit2.0 源码的同学都知道,其中有一个GsonConverterFactory 里面的用法十分精炼老成,这里来一段源码

据说使用TypeAdapter 效率更高,本人还未对比测试,暂时放后吧,TypeAdapter是什么玩意呢？

在源码中备注了一句 Converts Java objects to and from JSON 就是对象json之间的互相转换接替了T 泛型类的序列化和反序列化的逻辑

从源码中我们看到区分了2.1版本之前后之后的用法，2.1版本之前可以自定义adapter:

public class PointAdapter extends TypeAdapter<Point> {
 *     public Point read(JsonReader reader) throws IOException {
 *       if (reader.peek() == JsonToken.NULL) {
 *         reader.nextNull();
 *         return null;
 *       }
 *       String xy = reader.nextString();
 *       String[] parts = xy.split(",");
 *       int x = Integer.parseInt(parts[0]);
 *       int y = Integer.parseInt(parts[1]);
 *       return new Point(x, y);
 *     }
 *     public void write(JsonWriter writer, Point value) throws IOException {
 *       if (value == null) {
 *         writer.nullValue();
 *         return;
 *       }
 *       String xy = value.getX() + "," + value.getY();
 *       writer.value(xy);
 *     }
 *   }}

使用

GsonBuilder builder = new GsonBuilder();
 *   builder.registerTypeAdapter(Point.class, new PointAdapter());
 *   // if PointAdapter didn't check for nulls in its read/write methods, you should instead use
 *   // builder.registerTypeAdapter(Point.class, new PointAdapter().nullSafe());
 *   ...
 *   Gson gson = builder.create();

在2.1版本之后更推荐直接插入泛型就使用

//   String json = "{'origin':'0,0','points':['1,2','3,4']}";
//   TypeAdapter<Graph> graphAdapter = gson.getAdapter(Graph.class);
//   Graph graph = graphAdapter.fromJson(json);
// }</pre>
// And an example for serialization: <pre>   {@code
//
//   Graph graph = new Graph(...);
//   TypeAdapter<Graph> graphAdapter = gson.getAdapter(Graph.class);
//   String json = graphAdapter.toJson(graph);
// }</pre>

   实例:使用TypeAdapter 来序列化和反序列化

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.TypeAdapter;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest7 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        public int age;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        Gson gson = new Gson();
        TypeAdapter<User> userTypeAdapter = gson.getAdapter(User.class);
        User user = new User();
        user.name = "xuanyouwu";
        user.age = 26;
        String userJsonStr = userTypeAdapter.toJson(user);
        log("------>序列化:" + userJsonStr);
        User user1 = userTypeAdapter.fromJson(userJsonStr);
        log("------>反序列化:" + user1);
    }
}

运行结果:

------>序列化:{"name":"xuanyouwu","age":26}
------>反序列化:User{name='xuanyouwu', age=26}

Gson的容错机制:

   为什么要容错了,在javaBean中声明了int类型的age 如果服务端 返回的是"" 空字符串怎么办呢？崩溃？

   如果json格式不规范如 {name=zhangsan,age:26,hobby=null}  发现不是普通的key value

  容错实现方式1：

  1:创建Gson的方式

  gson = new GsonBuilder()
                    .setLenient()// json宽松
                    .create();

2:使用JsonReader

   JsonReader jsonReader = gson.newJsonReader(value.charStream());

   jsonReader.<span style="font-family: 宋体; font-size: 9pt;">setLenient(true)</span>

3:自定义TypeAdapter

4:使用注解JsonAdapter,其实也是自定义Adapter

1.2归为一类由框架实现,基本json大格式规范,键值对不标准,多引号的问题等等,而不报错停止解析,但是功能相对较弱

能解决bug

com.google.gson.JsonSyntaxException: com.google.gson.stream.MalformedJsonException: Use JsonReader.setLenient(true) to accept malformed JSON

3,4归为一类,都属于自定义adapter,但是3与gson绑定,4使用注解和字段绑定

实例：

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonParseException;
import com.google.gson.TypeAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest8 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        public int age;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
        ;
    }
    public static class UserTypeAdapter extends TypeAdapter<User> {
        @Override
        public void write(JsonWriter out, User value) throws IOException {
            out.beginObject();
            out.name("name").value(value.name);
            out.name("age").value(value.age);
            out.endObject();
        }
        @Override
        public User read(JsonReader in) throws IOException {
            User user = new User();
            in.beginObject();
            while (in.hasNext()) {
                switch (in.nextName()) {
                    case "name":
                        user.name = in.nextString();
                        break;
                    case "age":
                        try {
                            String str = in.nextString();
                            user.age = Integer.valueOf(str);
                        } catch (Exception e) {
                        }
                        break;
                }
            }
            in.endObject();
            return user;
        }
    }
    public static void main(String[] args) throws Exception {
        Gson gson = new Gson();
        String jsonStrFromServer = "{\n" +
                "    \"age\": \"\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        log("------->jsonFromServer:"+jsonStrFromServer);
        try {
            User user = gson.fromJson(jsonStrFromServer, User.class);
            log("------>默认Gson 解析:" + user);
        } catch (JsonParseException e) {//java.lang.NumberFormatException: empty String
            log("------>默认Gson 解析 异常:" + e);
        }
        Gson gson2 = new GsonBuilder()
                .registerTypeAdapter(User.class, new UserTypeAdapter()).create();
        try {
            User user2 = gson2.fromJson(jsonStrFromServer, User.class);
            log("------>自定义adapter 解析:" + user2);
        } catch (JsonParseException e) {//java.lang.NumberFormatException: empty String
            log("------>自定义adapter 异常:" + e);
        }
        try {
            UserTypeAdapter userTypeAdapter = new UserTypeAdapter();
            User user3 = userTypeAdapter.fromJson(jsonStrFromServer);
            log("------>自定义adapter 解析2:" + user3);
        } catch (Exception e) {
            log("------>自定义adapter 异常2:" + e);
        }
    }
}

运行结果:

------->jsonFromServer:{
"age": "",
"name": "zhangsan"
}
------>默认Gson 解析异常:com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: empty String
------>自定义adapter 解析:User{name='zhangsan', age=0}
------>自定义adapter 解析2:User{name='zhangsan', age=0}

可以看到 age是空字符串但是不影响整体的解析流程,这对客户端是十分友好的

基于注解的方式,上面的方式倾向于整体,注解的方式倾向于字段

package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.JsonParseException;
import com.google.gson.TypeAdapter;
import com.google.gson.annotations.JsonAdapter;
import com.google.gson.stream.JsonReader;
import com.google.gson.stream.JsonWriter;
import java.io.IOException;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest9 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        @JsonAdapter(IntegerTypeAdapter.class)
        public int age;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    public static class IntegerTypeAdapter extends TypeAdapter<Integer> {
        @Override
        public void write(JsonWriter out, Integer value) throws IOException {
            out.value(value);
        }
        @Override
        public Integer read(JsonReader in) throws IOException {
            int i = 0;
            try {
                String str = in.nextString();
                i = Integer.valueOf(str);
            } catch (Exception e) {
            }
            return i;
        }
    }
    public static class User2 {
        public String name;
        public int age;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        Gson gson = new Gson();
        String jsonStrFromServer = "{\n" +
                "    \"age\": \"\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        log("------->jsonFromServer:" + jsonStrFromServer);
        try {
            User2 user2 = gson.fromJson(jsonStrFromServer, User2.class);
            log("------>gson 解析:" + user2);
        } catch (Exception e) {
            log("------>gson 解析异常:" + e);
        }
        try {
            User user = gson.fromJson(jsonStrFromServer, User.class);
            log("------>JsonAdapter 注解 解析:" + user);
        } catch (JsonParseException e) {//java.lang.NumberFormatException: empty String
            log("------>JsonAdapter 注解 异常:" + e);
        }
    }
}

运行结果:

------->jsonFromServer:{
    "age": "",
    "name": "zhangsan"
}
------>gson 解析异常:com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: empty String
------>JsonAdapter 注解 解析:User{name='zhangsan', age=0}

可以看到我们成功地跳过服务端返回json不合理的坑了吧

</pre><pre code_snippet_id="1687762" snippet_file_name="blog_20160519_47_1535429" name="code" class="java">不得不吐槽啊，像这种服务器端错误，应该完全归结服务端json不合理返回，

往往老板都会找客户端原因，怎么又崩溃了？怎么又不显示了？老板不会关心是不是数据返回不合理的问题的！

做客户端需要相当的承受能力哈,同意的点个赞哈

</pre><p>其实上面的方式保险是很保险，但是需要维护的地方多，代码量大，我们介绍另外一种方式:JsonSerializer与JsonDeserializer 之关系单方面的处理，可以全局注册某个类型的处理：看实例：</p><p><pre name="code" class="java">package com.xuan.gson;
import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonDeserializationContext;
import com.google.gson.JsonDeserializer;
import com.google.gson.JsonElement;
import com.google.gson.JsonParseException;
import java.lang.reflect.Type;
/**
 * @author xuanyouwu
 * @email xuanyouwu@163.com
 * @time 2016-05-18 11:20
 */
public class GsonTest10 {
    private static void log(String msg) {
        System.out.println(msg);
    }
    public static class User {
        public String name;
        public int age;
        @Override
        public String toString() {
            return "User{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
    public static void main(String[] args) throws Exception {
        JsonDeserializer<Integer> jsonDeserializer = new JsonDeserializer<Integer>() {
            @Override
            public Integer deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
                try {
                    return json.getAsInt();
                } catch (NumberFormatException e) {
                    return 0;
                }
            }
        };
        Gson gson = new GsonBuilder()
                .registerTypeAdapter(int.class, jsonDeserializer)
                .create();
        String jsonStrFromServer = "{\n" +
                "    \"age\": \"\",\n" +
                "    \"name\": \"zhangsan\"\n" +
                "}";
        log("------->jsonFromServer:" + jsonStrFromServer);
        try {
            User user = gson.fromJson(jsonStrFromServer, User.class);
            log("------>  JsonDeserializer<Integer> 解析:" + user);
        } catch (Exception e) {
            log("------>  JsonDeserializer<Integer> 解析异常:" + e);
        }
        Gson gson1=new Gson();
        try {
            User user1 = gson1.fromJson(jsonStrFromServer, User.class);
            log("------> 默认gson 解析:" + user1);
        } catch (Exception e) {
            log("------>  默认gson 解析异常:" + e);
        }
    }
}

运行结果:

------->jsonFromServer:{
"age": "",
"name": "zhangsan"
}
------> JsonDeserializer<Integer> 解析:User{name='zhangsan', age=0}
------> 默认gson 解析异常:com.google.gson.JsonSyntaxException: java.lang.NumberFormatException: empty String

这样定义全局的反序列化工具就能避免解析异常