gson使用教程-翻譯4

原文地址:http://www.studytrails.com/java/json/java-google-json-serializing-collections.jsp

Serializing list

將Colloections轉成json就跟對象轉成json一樣.但是,問題在於Collections是可以有泛型的．所以在我們進行解析的時候需要將泛型的類型傳進對應的方法裏面.需要注意的是如果Collection中有不一樣的類型，那麼將無法進行解析．

以下就是示例代碼:

>() {}.getType();
        List datasets = gson.fromJson(json, datasetListType);
        for (Dataset dataset : datasets) {
            System.out.println(dataset.getAlbum_title());
            System.out.println(dataset.getAlbum_id());
        }
        // Prints
        //album1
        //1
        //album2
        //2
    }
}" data-snippet-id="ext.8f9d091ade9603c7228cea570561db37" data-snippet-saved="false" data-csrftoken="wxInFRZY-upUb_4SBj56fFTapdh99tBVPdGs" data-codota-status="done">package com.studytrails.json.gson;

import java.lang.reflect.Type;
import java.util.Collection;
import java.util.List;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class DeSerializeListExample5 {
    public static void main(String[] args) {
        String json = "[{album_id:1,album_title:'album1'},{album_id:2,album_title:'album2'}]";

        Gson gson = new Gson();
        // create the type for the collection. In this case define that the collection is of type Dataset
        Type datasetListType = new TypeToken<Collection<Dataset>>() {}.getType();
        List<Dataset> datasets = gson.fromJson(json, datasetListType);
        for (Dataset dataset : datasets) {
            System.out.println(dataset.getAlbum_title());
            System.out.println(dataset.getAlbum_id());
        }
        // Prints
        //album1
        //1
        //album2
        //2
    }
}

DataSet類:

 otherProperties = new HashMap();
     public String getAlbum_id() {
        return album_id;
    }
     public void setAlbum_id(String album_id) {
        this.album_id = album_id;
    }
     public String getAlbum_title() {
        return album_title;
    }
    public void setAlbum_title(String album_title) {
        this.album_title = album_title;
    }
    public Object get(String name) {
        return otherProperties.get(name);
    }
}" data-snippet-id="ext.be7a5a225823cc78e314e602aa3fd029" data-snippet-saved="false" data-csrftoken="02dpYMPM-Ty4ZHIBj3_ITwM1fXe5AlfzlKCA" data-codota-status="done">package com.studytrails.json.gson;
 import java.util.HashMap;
import java.util.Map;

public class Dataset {
    private String album_id;
    private String album_title;
    private Map<String , Object> otherProperties = new HashMap<String , Object>();
     public String getAlbum_id() {
        return album_id;
    }
     public void setAlbum_id(String album_id) {
        this.album_id = album_id;
    }
     public String getAlbum_title() {
        return album_title;
    }
    public void setAlbum_title(String album_title) {
        this.album_title = album_title;
    }
    public Object get(String name) {
        return otherProperties.get(name);
    }
}

同樣的在一些使用泛型的普通java類型面對同樣的問題．Gsont提供一個TypeToken的類來保存泛型的類型信息下面的demo中展示瞭如何使用TypeToken這個類來轉換和解析有泛型的普通類．

 animal = new Animal();
        // Create a Dog instance
        Dog dog = new Dog("I am a dog");

        animal.setAnimal(dog);
        Gson gson = new Gson();
        // Define a Type that is an Animal of type dog.
        Type animalType = new TypeToken>() {
        }.getType();

        // we first convert the animal object to a json and then read the json
        // back. However we define the json to be of Animal type
        Animal animal1 = gson.fromJson(gson.toJson(animal, animalType), Animal.class);
        System.out.println(animal1.get().getClass()); // prints class
                                                        // com.google.gson.internal.LinkedTreeMap

        // In contrast to above where we read the json back using the Animal
        // type, here we read the json back as the custom animalType Type. This
        // gives Gson an idea of what
        // the generic type should be.
        Animal animal2 = gson.fromJson(gson.toJson(animal), animalType);
        System.out.println(animal2.get().getClass());
        // prints class com.studytrails.json.gson.Dog

    }
}" data-snippet-id="ext.5763325dc80adb719d96612af9843b1f" data-snippet-saved="false" data-csrftoken="whIW2m9G-MB4Cy6cV1Ike3o7K_4kXf7h9kaI" data-codota-status="done">package com.studytrails.json.gson;

import java.lang.reflect.Type;

import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;

public class GenericTypesExample8 {
    public static void main(String[] args) {
        // create an animal class that is of type dog.
        Animal<dog> animal = new Animal<Dog>();
        // Create a Dog instance
        Dog dog = new Dog("I am a dog");

        animal.setAnimal(dog);
        Gson gson = new Gson();
        // Define a Type that is an Animal of type dog.
        Type animalType = new TypeToken<Animal<Dog>>() {
        }.getType();

        // we first convert the animal object to a json and then read the json
        // back. However we define the json to be of Animal type
        Animal animal1 = gson.fromJson(gson.toJson(animal, animalType), Animal.class);
        System.out.println(animal1.get().getClass()); // prints class
                                                        // com.google.gson.internal.LinkedTreeMap

        // In contrast to above where we read the json back using the Animal
        // type, here we read the json back as the custom animalType Type. This
        // gives Gson an idea of what
        // the generic type should be.
        Animal animal2 = gson.fromJson(gson.toJson(animal), animalType);
        System.out.println(animal2.get().getClass());
        // prints class com.studytrails.json.gson.Dog

    }
}

Animal類:

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類:

package com.studytrails.json.gson;

public class Dog {
    private String name;

    public Dog(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

}