java 无限递归遍历json对象

秒速五厘米 2021-09-02 05:00 871阅读 0赞

### 需求 ###

给一个json字符串，遍历json字符串，输出其每个key对应的value。举一个例子：

{
        "a":1,
        "b":{
            "b1":2
        }
    }

能够输出：a->1；b.b1->2

上例只是为了说明问题举得一个最简单的json，实际应用中json可以是嵌套非常复杂的结构。

### 方案 ###

**1、采用递归的方法打印每个路径上的值：**

static final String json_schema2 = "{\"a\":1,\"b\":{\"b1\":2},\"c\":[1,2,3,4],\"d\":{\"d1\":{\"d1_1\":100,\"d1_2\":101},\"d2\":[\"d2_1\",\"d2_2\"]},\"e\":[{\"e1\":1},{\"e2\":2}]}";
    
    static void  analysisJson(Object objJson){
        	//如果objJson为json数组
        	if(objJson instanceof JSONArray) {
        		JSONArray objArray = (JSONArray)objJson;
    			for (int i = 0; i < objArray.size(); i++) {
    				analysisJson(objArray.get(i));
    			}
        	} else if(objJson instanceof JSONObject) { //如果objJson为json对象
        		JSONObject jsonObject = (JSONObject)objJson;
    			Iterator it = jsonObject.keySet().iterator();
    			while(it.hasNext()) {
    				String key = it.next().toString();
    				Object value = jsonObject.get(key); //value
    				if(value instanceof JSONArray) { //如果value是数组
    					JSONArray objArray = (JSONArray)value;
    					analysisJson(objArray);
    				} else if(value instanceof JSONObject){ //如果value是json对象
    					analysisJson((JSONObject)value);
    				} else { //如果value是基本类型
    					System.out.println("["+key+"]:"+value.toString()+" ");
    				}
    			}
        	} else { //objJson为基本类型
        		System.out.println(objJson.toString()+" ");
        	}
        }

输出：

[a]:1 
    [b1]:2 
    1 
    2 
    3 
    4 
    [d1_1]:100 
    [d1_2]:101 
    d2_1 
    d2_2 
    [e1]:1 
    [e2]:2

参考：[https://blog.csdn.net/UpdateAllTheTime/article/details/82789034][https_blog.csdn.net_UpdateAllTheTime_article_details_82789034]

上面的方法虽然可以输出json对象中的每个值，但是丢失了json结构中key的路径，此外对于数组接口，没有输出key。

对上面方法进行优化：

static void  analysisJson2(Object objJson,String flag) {
        	if(objJson instanceof JSONArray) {//如果obj为json数组
        		JSONArray objArray = (JSONArray)objJson;
    			for (int i = 0; i < objArray.size(); i++) {
    				analysisJson2(objArray.get(i),flag);
    			}
        	} else if(objJson instanceof JSONObject){//如果为json对象
        		JSONObject jsonObject = (JSONObject)objJson;
    			Iterator it = jsonObject.keySet().iterator();
    			while(it.hasNext()) {
    				String key = it.next().toString();
    				Object object = jsonObject.get(key);
    				//如果得到的是数组
    				if(object instanceof JSONArray){
    					JSONArray objArray = (JSONArray)object;
    					String path = "";
    					if (StringUtils.isNotBlank(flag)) {
    						path = flag + "." + key;
    					} else {
    						path = key;
    					}
    					analysisJson2(objArray,path);
    				} else if(object instanceof JSONObject) {//如果key中是一个json对象
    					String path = "";
    					if (StringUtils.isNotBlank(flag)) {
    						path = flag + "." + key;
    					} else {
    						path = key;
    					}
    					analysisJson2((JSONObject)object,path);
    				} else {//如果key中是其他
    					String path = "";
    					if (StringUtils.isNotBlank(flag)) {
    						path = flag + "." + key;
    					} else {
    						path = key;
    					}
    					System.out.println(path+":"+object.toString()+" ");
    				}
    			}
        	} else {//如果key中是其他
    			System.out.println(flag+":"+objJson.toString()+" ");
    		}
        }

输出：

a:1 
    b.b1:2 
    c:1 
    c:2 
    c:3 
    c:4 
    d.d1.d1_1:100 
    d.d1.d1_2:101 
    d.d2:d2_1 
    d.d2:d2_2 
    e.e1:1 
    e.e2:2

非常完美，吧json结构中key的每个路径都保存了下来。但是，还是有一点点的小瑕疵，对于数组结构，没有输出下标值。

**2、json-flatter库：**

github：[https://github.com/wnameless/json-flattener][https_github.com_wnameless_json-flattener]

json-flatter库可以将json结构按照上面需求输出，同时对于数组还能显示下标。例如：

{ "a":
      { "b": 1,
        "c": null,
        "d": [false, true]
      },
      "e": "f",
      "g": 2.3
    }
    //输出
    { "a.b": 1,
      "a.c": null,
      "a.d[0]": false,
      "a.d[1]": true,
      "e": "f",
      "g": 2.3
    }

示例：

<dependency>
    	<groupId>com.github.wnameless.json</groupId>
    	<artifactId>json-flattener</artifactId>
    	<version>0.9.0</version>
    </dependency>

String json = "{ \"a\" : { \"b\" : 1, \"c\": null, \"d\": [false, true] }, \"e\": \"f\", \"g\":2.3 }";
    Map<String, Object> flattenJson = JsonFlattener.flattenAsMap(json);
    
    System.out.println(flattenJson);
    // Output: {a.b=1, a.c=null, a.d[0]=false, a.d[1]=true, e=f, g=2.3}
    
    String jsonStr = JsonFlattener.flatten(json);
    System.out.println(jsonStr);
    // Output: {"a.b":1,"a.c":null,"a.d[0]":false,"a.d[1]":true,"e":"f","g":2.3}
    
    String nestedJson = JsonUnflattener.unflatten(jsonStr);
    System.out.println(nestedJson);
    // {"a":{"b":1,"c":null,"d":[false,true]},"e":"f","g":2.3}
    
    // Support JSON keys which contain dots or square brackets
    String flattendJsonWithDotKey = JsonFlattener.flatten("[{\"a.a.[\":1},2,{\"c\":[3,4]}]");
    System.out.println(flattendJsonWithDotKey);
    // Output: {"[0][\"a.a.[\"]":12,"[1]":2,"[2].c[0]":3,"[2].c[1]":4}
    
    String nestedJsonWithDotKey = JsonUnflattener.unflatten(
            "{\"[1][0];\":2,\"[0]\":1,\"[1][1]\":3,\"[2]\":4,\"[3][\\\"ab.c.[\\\"]\":5}");
    System.out.println(nestedJsonWithDotKey);
    // Output: [1,[2,3],4,{"ab.c.[":5}]

[https_blog.csdn.net_UpdateAllTheTime_article_details_82789034]: https://blog.csdn.net/UpdateAllTheTime/article/details/82789034
[https_github.com_wnameless_json-flattener]: https://github.com/wnameless/json-flattener