Android 利用Gson生成或解析json

目前手机端和服务端数据交流格式一般是json，而谷歌提供了Gson来解析json。下载Gson:https://code.google.com/p/google-gson/

下载的放在lib并导入，若出现错误：java.lang.NoClassDefFoundError: com.google.gson.Gson

是因为没有导入android-support-v4.jar，导入即可。

一、单个对象生成json

生成以下类，该怎么生成呢？

{
    "createDate": "2015-02-01 10:39:50",
    "id": "1",
    "name": "传说之美",
    "password": "123456"
}

先定义一个account类,属性有id、name、password、createDate。

public class Account {
	private String id;
	private String password;
	private String name;
	private String createDate;
	public Account() {
		super();
	}
	public Account(String id, String password, String name, String createDate) {
		super();
		this.id = id;
		this.password = password;
		this.name = name;
		this.createDate = createDate;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getCreateDate() {
		return createDate;
	}
	public void setCreateDate(String createDate) {
		this.createDate = createDate;
	}
	@Override
	public String toString() {
		return "Account [id=" + id + ", password=" + password + ", name=" + name + ", createDate=" + createDate + "]\n\n";
	}
}

定义好这个类，就可以利用Gson生成json字符串了。

		// 生成account对象
		SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd hh:mm:ss");
		Account account = new Account("1", "123456", "传说之美", sdf.format(new Date()));

		// 利用gson对象生成json字符串
		Gson gson = new Gson();
		String jsonString = gson.toJson(account);
                Log.i("", jsonString);

输入的log如下

二、解析json字符串为单个对象

在上面已生成了jsonString，那如何将其解析为单个对象，很简单。

		// 利用gson解析json字符串为单个对象
		Account account1 = gson.fromJson(jsonString, Account.class);
		Log.i("", account1.toString());

看看输出的log

三、生成单个对象的json数组

什么事json数组，类似下面的

[
    {
        "id": "2",
        "createDate": "2015-02-01 11:21:27",
        "password": "123456",
        "name": "传说"
    },
    {
        "id": "2",
        "createDate": "2015-02-01 11:21:27",
        "password": "123456",
        "name": "之美"
    }
]

生成json数组代码如下

		Account account2 = new Account("2", "123456", "传说", sdf.format(new Date()));
		Account account3 = new Account("2", "123456", "之美", sdf.format(new Date()));
		List<Account> accountList = new ArrayList<Account>();
		accountList.add(account2);
		accountList.add(account3);

		JSONArray accountArray = new JSONArray();
		for (int i = 0; i < accountList.size(); i++) {
			String accountStr = gson.toJson(accountList.get(i));
			JSONObject accountObject;
			try {
				accountObject = new JSONObject(accountStr);
				accountArray.put(i, accountObject);
			} catch (JSONException e) {
				e.printStackTrace();
			}
		}
		Log.i("", accountArray.toString());

log的输出为

四、由多个单个对象的json数组解析为对个单个对象

多个单个对象组成的json数组解析如下

		// 解析json数组
		List<Account> accountList2 = new ArrayList<Account>();
		for(int i=0;i<accountArray.length(); i++){
			JSONObject jsonObject = null;
			try {
				jsonObject = accountArray.getJSONObject(i);
			} catch (JSONException e) {
				e.printStackTrace();
			}
			if(jsonObject != null){
				Account tempAccount = gson.fromJson(jsonObject.toString(), Account.class);
				accountList2.add(tempAccount);
			}
		}
		Log.i("accountList2", accountList2.toString());

输出的log

或者用更快捷的转化方法

		Account[] accountArrays = new Gson().fromJson(accountArray.toString(), Account[].class);
		for(int i=0;i<accountArrays.length;i++){
			Log.i("accountArrays",accountArrays[i].toString());
		}
		// 转化为List
		List<Account> foosList = Arrays.asList(accountArrays);

更快捷地解析成List

		// 更快捷地解析成List
		Type listType = new TypeToken<ArrayList<Account>>(){}.getType();
		ArrayList<Account> accsList = new Gson().fromJson(accountArray.toString(), listType);
		Log.i("accsList",accsList.toString());

五、生成一个对象嵌套对象的json

嵌套的json类似如下

{
    "member": {
        "id": "4",
        "name": "我是传说"
    },
    "id": "4",
    "createDate": "2015-02-02 12:03:32",
    "password": "888888",
    "name": "传说之美"
}

生成这个json有2种方法。

1、再添加一个member类，像添加account类一样添加即可。

public class Member {
	private String id;
	private String name;
	public Member() {
		super();
	}
	public Member(String id, String name) {
		super();
		this.id = id;
		this.name = name;
	}
	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	@Override
	public String toString() {
		return "Member [id=" + id + ", name=" + name + "]\n\n";
	}
}

生成代码如下

		// 生成对象嵌套对象的json
		Account account4 = new Account("4", "888888", "传说之美", sdf.format(new Date()));
		Member member = new Member("4", "我是传说");
		String accountStr = gson.toJson(account4);
		String memberStr = gson.toJson(member);
		JSONObject object = null;
		try {
			JSONObject memberObject = new JSONObject(memberStr);
			object = new JSONObject(accountStr);
			object.put("member", memberObject);
		} catch (JSONException e) {
			e.printStackTrace();
		}
		Log.i("", object.toString());

输出的log

六、解析对象嵌套对象的json 

		Account account5 = gson.fromJson(object.toString(), Account.class);
		Log.i("解析对象嵌套对象的json", account5.toString());
		// 这里用isNull来判断是否存在这个object，存在就拿出member的JSONObject
		JSONObject memberObject = null;
		if(!object.isNull("member")){
			try {
				memberObject = object.getJSONObject("member");
			} catch (JSONException e) {
				e.printStackTrace();
			}
		}
		Member member5 = null;
		if(null != memberObject){
			member5 = gson.fromJson(memberObject.toString(), Member.class);
			Log.i("解析对象嵌套对象的json", member5.toString());
		}

输出的结果

 7、另外一种解析对象嵌套对象的json 

定义一个类

public class AccountObject {
	private String id;
	private String password;
	private String name;
	private String createDate;
	private MemberObject memberObject = new MemberObject();

	public class MemberObject {
		private String id;
		private String name;
		@Override
		public String toString() {
			return "MemberObject [id=" + id + ", name=" + name+ "]\n\n";
		}
	}
	@Override
	public String toString() {
		return "AccountObject [id=" + id + ", password=" + password + ", name=" + name + ", createDate=" + createDate + ","+ memberObject.toString() + "]\n\n";
	}
}

生成json并解析

		try {
			JSONObject mObject = new JSONObject(memberStr);
			object = new JSONObject(accountStr);
			object.put("memberObject", mObject);
		} catch (JSONException e) {
			e.printStackTrace();
		}
		AccountObject accountObject = gson.fromJson(object.toString(), AccountObject.class);
		Log.i("accountObject", accountObject.toString());

打印出来的log

本文博客原创地址：http://www.cnblogs.com/liqw/p/4266209.html

demo下载链接：http://files.cnblogs.com/files/liqw/LauncherActivity.zip