Java 提取json中的文字

1. 簡單的 json 文字

 {"result":
 	{
 		"code":1,
	    "msg":"success",
   		"url":"",
	    "data":"0",
   		"date":"1530007139"
 	},
	"data":
	{
		"token":"iamtoken",
		"life":1530005620,
	   "expires":7200
   }
 }

2. 需求

如果需要提取code中的值，該怎麼做呢？如果需要提取token中的值又該怎麼做呢？需要藉助Alibaba的一個jar 包，其maven依賴如下：

<!-- https://mvnrepository.com/artifact/com.alibaba/fastjson -->
<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>fastjson</artifactId>
    <version>1.2.53</version>
</dependency>

實現上述需求的程式碼如下：

package utils;

import com.alibaba.fastjson.
 
JSONObject;

public class JsonUtils {
    //get a normal string by json string
    public static void main(String[] args) {
        String content = "{\"result\":{\"code\":1,\"msg\":\"success\",\"url\":\"\",\"data\":\"0\",\"date\":\"1530007139\"},\"data\":{\"token\":\"iamtoken\",\"life\":1530005620,\"expires\":7200}}"
 
;
        System.out.println("token: "+getToken(content));
        System.out.println("code: "+getCode(content));
    }

    public static String getCode(String content) {
        JSONObject jsonObject = JSONObject.parseObject(content);
        String code = jsonObject.getJSONObject("result").getString("code");
        return code;
    }

    public static String getToken(String content) {
        JSONObject jsonObject = JSONObject.parseObject(content);//將該字串解析成jsonObject
        String token = jsonObject.getJSONObject("data").getString("token");//提取該物件中的data域，
        return  token;
    }
}

3. 執行結果

4. 複雜的 json 文字

如果 json 文字如下所示，那麼該怎麼獲取呢？

對應的文字如下：

{"data":[
	{
		"id":524816977,
		"type":"answer",
		"relationship":
		{
			"is_author":false,
			"is_authorized":false,
			"is_nothelp":false,
			"is_thanked":false,
			"voting":0,
			"upvoted_followees":[]
		}
	},
	{
		"id":524816978,
		"type":"answer",
		"relationship":
		{
			"is_author":true,
			"is_authorized":false,
			"is_nothelp":false,
			"is_thanked":false,
			"voting":10,
			"upvoted_followees":[]
		}
	}
]}

可以看到這裡的 json相當於一個數組了。裡面裝有兩個json 物件，分別是：

	{
		"id":524816977,
		"type":"answer",
		"relationship":
		{
			"is_author":false,
			"is_authorized":false,
			"is_nothelp":false,
			"is_thanked":false,
			"voting":0,
			"upvoted_followees":[]
		}
	}

和

{
		"id":524816978,
		"type":"answer",
		"relationship":
		{
			"is_author":true,
			"is_authorized":false,
			"is_nothelp":false,
			"is_thanked":false,
			"voting":10,
			"upvoted_followees":[]
		}
	}

那麼該怎麼獲取這裡面的某個值呢？比如id的值。
如果此時還按照上述簡單json 文字的寫法，程式碼如下：

public void getValue() {
        String jsonString = "{\n" +
                "  \"data\": [\n" +
                "    {\n" +
                "      \"id\": 524816977,\n" +
                "      \"type\": \"answer\",\n" +
                "      \"relationship\": {\n" +
                "        \"is_author\": false,\n" +
                "        \"is_authorized\": false,\n" +
                "        \"is_nothelp\": false,\n" +
                "        \"is_thanked\": false,\n" +
                "        \"voting\": 0,\n" +
                "        \"upvoted_followees\": []\n" +
                "      }\n" +
                "    },\n" +
                "    {\n" +
                "      \"id\": 524816978,\n" +
                "      \"type\": \"answer\",\n" +
                "      \"relationship\": {\n" +
                "        \"is_author\": true,\n" +
                "        \"is_authorized\": false,\n" +
                "        \"is_nothelp\": false,\n" +
                "        \"is_thanked\": false,\n" +
                "        \"voting\": 10,\n" +
                "        \"upvoted_followees\": []\n" +
                "      }\n" +
                "    }\n" +
                "  ]\n" +
                "}";
        JSONObject jsonObject = JSONObject.parseObject(jsonString);
        System.out.println("id : "+jsonObject.getJSONObject("data").getJSONObject("id"));
    }

執行得到的結果是：

可以看到很明顯的錯誤就是：不能將一個JSONArray 轉換成一個 JSONObject物件，所以應該修改程式碼成如下的樣子：

public void getValue() {
        String jsonString = "{\n" +
                "  \"data\": [\n" +
                "    {\n" +
                "      \"id\": 524816977,\n" +
                "      \"type\": \"answer\",\n" +
                "      \"relationship\": {\n" +
                "        \"is_author\": false,\n" +
                "        \"is_authorized\": false,\n" +
                "        \"is_nothelp\": false,\n" +
                "        \"is_thanked\": false,\n" +
                "        \"voting\": 0,\n" +
                "        \"upvoted_followees\": []\n" +
                "      }\n" +
                "    },\n" +
                "    {\n" +
                "      \"id\": 524816978,\n" +
                "      \"type\": \"answer\",\n" +
                "      \"relationship\": {\n" +
                "        \"is_author\": true,\n" +
                "        \"is_authorized\": false,\n" +
                "        \"is_nothelp\": false,\n" +
                "        \"is_thanked\": false,\n" +
                "        \"voting\": 10,\n" +
                "        \"upvoted_followees\": []\n" +
                "      }\n" +
                "    }\n" +
                "  ]\n" +
                "}";
        JSONObject jsonObject = JSONObject.parseObject(jsonString);
        JSONArray data = jsonObject.getJSONArray("data");
        System.out.println("json size is: "+data.size());

        //print the
        for(int i = 0;i< data.size();i++) {
            //輸出其中每一個
            System.out.println(data.get(i).toString());
        }

        for(int i = 0 ;i< data.size();i++) {
            System.out.println("id: "+data.getJSONObject(i).getString("id"));
        }
    }

執行結果如下：

參考文章

• https://bbs.csdn.net/topics/392404716?page=1