gson使用教程-翻译7

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原文地址:http://www.studytrails.com/java/json/java-google-json-custom-serializer-deserializer.jsp

就如我们之前看到的教程,Gson提供自定义序列化器和反序列化器.如果我们不需要Gson默认的转换方式，我们可以通过自定义序列化器和反序列化器来转换java对象和json.下面的第一个demo是展示自定义序列化器和第二个demo是展示自定义反序列化器.

Custom Serializer

自定义序列化器通过实现JsonSerializer这个接口和实现public JsonElement serialize(T src,Type typeOfSrc,JsonSerializationContext context)方法,src这个是转换源对象，而Type是转换源对象的类型.下面的demo展示如何创建和使用自定义序列化器．

package com.studytrails.json.gson;import java.lang.reflect.Type;import com.google.gson.Gson;import com.google.gson.GsonBuilder;import com.google.gson.JsonElement;import com.google.gson.JsonObject;import com.google.gson.JsonSerializationContext;import com.google.gson.JsonSerializer;import com.google.gson.reflect.TypeToken;public class DogSerializer implements JsonSerializer<dog> {    @Override    public JsonElement serialize(Dog src, Type typeOfSrc, JsonSerializationContext context) {        // This method gets involved whenever the parser encounters the Dog        // object (for which this serializer is registered)        JsonObject object = new JsonObject();        String name = src.getName().replaceAll(" ", "_");        object.addProperty("name", name);        // we create the json object for the dog and send it back to the        // Gson serializer        return object;    }    public static void main(String[] args) {        Animall<Dog> animal = new Animall<Dog>();        Dog dog = new Dog("I am a dog");        animal.setAnimal(dog);        // Create the GsonBuilder and register a serializer for the Dog class.        // Whenever the Dog class is encountered Gson calls the DogSerializer        // we set pretty printing own to format the json        Gson gson = new GsonBuilder().registerTypeAdapter(Dog.class, new DogSerializer()).setPrettyPrinting().create();        // Since Animal contains generic type create the type using TypeToken        // class.        Type animalType = new TypeToken<Animal<Dog>>() {        }.getType();        System.out.println(gson.toJson(animal, animalType));    }}

Animal类

package com.studytrails.json.gson;public class Animal<t> {    public T animal;    public void setAnimal(T animal) {        this.animal = animal;    }    public T get() {        return animal;    }}

Dog类

package com.studytrails.json.gson;public class Dog {    private String name;    public Dog(String name) {        this.name = name;    }    public String getName() {        return name;    }}

Custom DeSerializer

使用一个自定义反序列化器把一个json转换成Dog对象.通过实现JsonDeserializer接口来自定义反序列化器．

  package com.studytrails.json.gson;import java.lang.reflect.Type;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 com.google.gson.reflect.TypeToken;public class DogDeserialiser implements JsonDeserializer<Dog> {    @Override    public Dog deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {        String name = json.getAsJsonObject().get("name").getAsString();        name = name.replace(" ", "_");        Dog dog = new Dog(name);        return dog;    }    public static void main(String[] args) {        String json = "{\"animal\":{\"name\":\"I am a dog\"}}";        Gson gson = new GsonBuilder().registerTypeAdapter(Dog.class, new DogDeserialiser()).create();        Type animalType = new TypeToken<Animal<Dog>>() {        }.getType();        Animal<Dog> animal = gson.fromJson(json, animalType);        System.out.println(animal.get().getName());    }}

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