Amdroid示例：利用Gson生成或解析json

转自:http://www.cnblogs.com/liqw/p/4266209.html

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？

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{
    "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。

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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 + "] ";
    }
}

定义好这个类，就可以利用Gson生成json字符串了。

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// 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。

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// 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

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[
    {
        "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

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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

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// 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

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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

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// 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

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{
    "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。

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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 + "] ";
    }
}

生成代码如下

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// 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 

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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

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

生成json并解析

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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

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原文地址：https://www.cnblogs.com/boonya/p/4332458.html