專案特點
GitHub專案地址：https://github.com/json-path/JsonPath
主要功能：
- 將Json字串轉為Java Map物件（這個不算什麼，FastJson之類的工具都可以）
- 通過強大的規則表示式定位欄位，返回欄位值或值集合（很厲害）
支援的規則表示式以及示例（選自專案readme）：
| JsonPath (點選測試) | 結果 |
|---|---|
| $.store.book[*].author | The authors of all books |
| $..author | All authors |
| $.store.* | All things, both books and bicycles |
| $.store..price | The price of everything |
| $..book[2] | The third book |
| $..book[-2] | The second to last book |
| $..book[0,1] | The first two books |
| $..book[:2] | All books from index 0 (inclusive) until index 2 (exclusive) |
| $..book[1:2] | All books from index 1 (inclusive) until index 2 (exclusive) |
| $..book[-2:] | Last two books |
| $..book[2:] | Book number two from tail |
| $..book[?(@.isbn)] | All books with an ISBN number |
| $.store.book[?(@.price < 10)] | All books in store cheaper than 10 |
| $..book[?(@.price <= $['expensive'])] | All books in store that are not "expensive" |
| $..book[?(@.author =~ /.*REES/i)] | All books matching regex (ignore case) |
| $..* | Give me every thing |
| $..book.length() | The number of books |
實戰測試
就用專案readme文件提供的例子進行測試：
json格式字串，點選檢視
{
"store": {
"book": [
{
"category": "reference",
"author": "Nigel Rees",
"title": "Sayings of the Century",
"price": 8.95
},
{
"category": "fiction",
"author": "Evelyn Waugh",
"title": "Sword of Honour",
"price": 12.99
},
{
"category": "fiction",
"author": "Herman Melville",
"title": "Moby Dick",
"isbn": "0-553-21311-3",
"price": 8.99
},
{
"category": "fiction",
"author": "J. R. R. Tolkien",
"title": "The Lord of the Rings",
"isbn": "0-395-19395-8",
"price": 22.99
}
],
"bicycle": {
"color": "red",
"price": 19.95
}
},
"expensive": 10
}
POM中引入依賴：
<dependency>
<groupId>com.jayway.jsonpath</groupId>
<artifactId>json-path</artifactId>
<version>2.7.0</version>
</dependency>
寫一個單元測試類：
@SpringBootTest
@RunWith(MockitoJUnitRunner.class)
public class JsonPathTest {
private final String jsonStr = "...";
private final Object context = Configuration.defaultConfiguration().jsonProvider().parse(jsonStr);
@Test
public void test(){}
}
其中：
- 第二個註解可以做到啟動SpringBoot測試類而無需啟動SpringApplication，並且也可以做到元件注入等功能。
- jsonStr用來指代之前所述的json字串，這裡簡略寫。
- context實際上是由json字串通過預設配置生成的一個Map<String, Object>。
先看看context的型別：
System.out.println("context的型別：" + context.getClass().getSimpleName() + "\n");
------------------------------------------------------------------
output: context的型別：LinkedHashMap
用法1：通過key定位一個value：
jsonpath = "$.store.book[1].price";
result = JsonPath.read(testMap, jsonpath);
System.out.println("contents on " + jsonpath + ": " + result + "\n");
------------------------------------------------------------------
output: contents on $.store.book[1].price: 12.99
用法2：通過key定位一組value：
jsonpath = "$.store.book[*].price";
result = JsonPath.read(context, jsonpath);
System.out.println("contents on " + jsonpath + ": " + result + "\n");
------------------------------------------------------------------
output: contents on $.store.book[*].price: [8.95,12.99,8.99,22.99]
這裡如果去檢視result的type，會發現它是JSONArray型別，是List<Object>介面的實現，當List用就可以了。
用法3：向下遞迴查詢：
jsonpath = "$..price";
result = JsonPath.read(context, jsonpath);
System.out.println("contents on " + jsonpath + ": " + result);
------------------------------------------------------------------
output: contents on $..price: [8.95,12.99,8.99,22.99,19.95]
在測試的時候想起一個問題，設想這樣的場景，如果我們已經有了這樣一個Map，只需要JsonPath提供的規則表示式解析與查詢能力，那麼想要使用JsonPath是不是需要Map->JsonString->context->規則解析->查詢結果？答案是不需要的。
我們已經知道這個context本就是一個Map型別，那麼是不是可以省去中間轉為json string的步驟呢？我們測試看看：
//1. 先將json解析為一個Map
Map<String, Object> testMap = (Map) JSONObject.parseObject(JSON_STRING);
jsonpath = "$..price";
//2. 再將Map傳入read方法，看是否能查詢到結果：
result = JsonPath.read(testMap, jsonpath);
System.out.println("contents on " + jsonpath + ": " + result);
------------------------------------------------------------------
output: contents on $..price: [8.95,12.99,8.99,22.99,19.95]
可以看出，JsonPath的搜尋規則解析能力是支援對普通Map進行查詢的。