Jayway JsonPath介绍

绝地灬酷狼 2021-06-22 15:38 384阅读 0赞

XML的一个经常强调的优点是可以使用大量工具来分析，转换和有选择地从XML文档中提取数据，[XPath][]是这些功能强大的工具之一。jsonPath类似Xpath，可以在json数据结构中进行分析。

对比XPath和JsonPath表达式如下：

<table> 
 <tbody> 
  <tr> 
   <td><strong>XPath</strong></td> 
   <td><strong>JSONPath</strong></td> 
   <td><strong>Description</strong></td> 
  </tr> 
  <tr> 
   <td>/</td> 
   <td>$</td> 
   <td>the root object/element</td> 
  </tr> 
  <tr> 
   <td>.</td> 
   <td>@</td> 
   <td>the current object/element</td> 
  </tr> 
  <tr> 
   <td>/</td> 
   <td>. or []</td> 
   <td>child operator</td> 
  </tr> 
  <tr> 
   <td>..</td> 
   <td>n/a</td> 
   <td>parent operator</td> 
  </tr> 
  <tr> 
   <td>//</td> 
   <td>..</td> 
   <td>recursive descent. JSONPath borrows this syntax from E4X.</td> 
  </tr> 
  <tr> 
   <td>*</td> 
   <td>*</td> 
   <td>wildcard. All objects/elements regardless their names.</td> 
  </tr> 
  <tr> 
   <td>@</td> 
   <td>n/a</td> 
   <td>attribute access. JSON structures don't have attributes.</td> 
  </tr> 
  <tr> 
   <td>[]</td> 
   <td>[]</td> 
   <td>subscript operator. XPath uses it to iterate over element collections and for&nbsp;<a href="http://www.w3.org/TR/xpath#predicates" rel="nofollow">predicates</a>. In Javascript and JSON it is the native array operator.</td> 
  </tr> 
  <tr> 
   <td>|</td> 
   <td>[,]</td> 
   <td>Union operator in XPath results in a combination of node sets. JSONPath allows alternate names or array indices as a set.</td> 
  </tr> 
  <tr> 
   <td>n/a</td> 
   <td>[start:end:step]</td> 
   <td>array slice operator borrowed from ES4.</td> 
  </tr> 
  <tr> 
   <td>[]</td> 
   <td>?()</td> 
   <td>applies a filter (script) expression.</td> 
  </tr> 
  <tr> 
   <td>n/a</td> 
   <td>()</td> 
   <td>script expression, using the underlying script engine.</td> 
  </tr> 
  <tr> 
   <td>()</td> 
   <td>n/a</td> 
   <td>grouping in Xpath</td> 
  </tr> 
 </tbody> 
</table>

Jayway JsonPath是[Stefan Goessner JsonPath ][Stefan Goessner JsonPath]的java版本实现，

*  github：[https://github.com/json-path/JsonPath][https_github.com_json-path_JsonPath]
 *  在线工具：[http://jsonpath.herokuapp.com/][http_jsonpath.herokuapp.com]

### Jayway JsonPath功能介绍 ###

1、JsonPath 表达式可以用 . 或者 \[\] 表示：

$.store.book[0].title
    或者
    $['store']['book'][0]['title']

2、操作符：

<table> 
 <thead> 
  <tr> 
   <th>Operator</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><code>$</code></td> 
   <td>The root element to query. This starts all path expressions.</td> 
  </tr> 
  <tr> 
   <td><code>@</code></td> 
   <td>The current node being processed by a filter predicate.</td> 
  </tr> 
  <tr> 
   <td><code>*</code></td> 
   <td>Wildcard. Available anywhere a name or numeric are required.</td> 
  </tr> 
  <tr> 
   <td><code>..</code></td> 
   <td>Deep scan. Available anywhere a name is required.</td> 
  </tr> 
  <tr> 
   <td><code>.&lt;name&gt;</code></td> 
   <td>Dot-notated child</td> 
  </tr> 
  <tr> 
   <td><code>['&lt;name&gt;' (, '&lt;name&gt;')]</code></td> 
   <td>Bracket-notated child or children</td> 
  </tr> 
  <tr> 
   <td><code>[&lt;number&gt; (, &lt;number&gt;)]</code></td> 
   <td>Array index or indexes</td> 
  </tr> 
  <tr> 
   <td><code>[start:end]</code></td> 
   <td>Array slice operator</td> 
  </tr> 
  <tr> 
   <td><code>[?(&lt;expression&gt;)]</code></td> 
   <td>Filter expression. Expression must evaluate to a boolean value.</td> 
  </tr> 
 </tbody> 
</table>

3、函数：

<table> 
 <thead> 
  <tr> 
   <th>Function</th> 
   <th>Description</th> 
   <th>Output</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>min()</td> 
   <td>Provides the min value of an array of numbers</td> 
   <td>Double</td> 
  </tr> 
  <tr> 
   <td>max()</td> 
   <td>Provides the max value of an array of numbers</td> 
   <td>Double</td> 
  </tr> 
  <tr> 
   <td>avg()</td> 
   <td>Provides the average value of an array of numbers</td> 
   <td>Double</td> 
  </tr> 
  <tr> 
   <td>stddev()</td> 
   <td>Provides the standard deviation value of an array of numbers</td> 
   <td>Double</td> 
  </tr> 
  <tr> 
   <td>length()</td> 
   <td>Provides the length of an array</td> 
   <td>Integer</td> 
  </tr> 
  <tr> 
   <td>sum()</td> 
   <td>Provides the sum value of an array of numbers</td> 
   <td>Double</td> 
  </tr> 
 </tbody> 
</table>

4、过滤器：

<table> 
 <thead> 
  <tr> 
   <th>Operator</th> 
   <th>Description</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td>==</td> 
   <td>left is equal to right (note that 1 is not equal to '1')</td> 
  </tr> 
  <tr> 
   <td>!=</td> 
   <td>left is not equal to right</td> 
  </tr> 
  <tr> 
   <td>&lt;</td> 
   <td>left is less than right</td> 
  </tr> 
  <tr> 
   <td>&lt;=</td> 
   <td>left is less or equal to right</td> 
  </tr> 
  <tr> 
   <td>&gt;</td> 
   <td>left is greater than right</td> 
  </tr> 
  <tr> 
   <td>&gt;=</td> 
   <td>left is greater than or equal to right</td> 
  </tr> 
  <tr> 
   <td>=~</td> 
   <td>left matches regular expression [?(@.name =~ /foo.*?/i)]</td> 
  </tr> 
  <tr> 
   <td>in</td> 
   <td>left exists in right [?(@.size in ['S', 'M'])]</td> 
  </tr> 
  <tr> 
   <td>nin</td> 
   <td>left does not exists in right</td> 
  </tr> 
  <tr> 
   <td>subsetof</td> 
   <td>left is a subset of right [?(@.sizes subsetof ['S', 'M', 'L'])]</td> 
  </tr> 
  <tr> 
   <td>anyof</td> 
   <td>left has an intersection with right [?(@.sizes anyof ['M', 'L'])]</td> 
  </tr> 
  <tr> 
   <td>noneof</td> 
   <td>left has no intersection with right [?(@.sizes noneof ['M', 'L'])]</td> 
  </tr> 
  <tr> 
   <td>size</td> 
   <td>size of left (array or string) should match right</td> 
  </tr> 
  <tr> 
   <td>empty</td> 
   <td>left (array or string) should be empty</td> 
  </tr> 
 </tbody> 
</table>

5、示例：

{
        "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
    }

JsonPath表达式：

<table> 
 <thead> 
  <tr> 
   <th>JsonPath (click link to try)</th> 
   <th>Result</th> 
  </tr> 
 </thead> 
 <tbody> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$.store.book%5B*%5D.author" rel="nofollow">$.store.book[*].author</a></td> 
   <td>The authors of all books</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..author" rel="nofollow">$..author</a></td> 
   <td>All authors</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$.store.*" rel="nofollow">$.store.*</a></td> 
   <td>All things, both books and bicycles</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$.store..price" rel="nofollow">$.store..price</a></td> 
   <td>The price of everything</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B2%5D" rel="nofollow">$..book[2]</a></td> 
   <td>The third book</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B2%5D" rel="nofollow">$..book[-2]</a></td> 
   <td>The second to last book</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B0,1%5D" rel="nofollow">$..book[0,1]</a></td> 
   <td>The first two books</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B:2%5D" rel="nofollow">$..book[:2]</a></td> 
   <td>All books from index 0 (inclusive) until index 2 (exclusive)</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B1:2%5D" rel="nofollow">$..book[1:2]</a></td> 
   <td>All books from index 1 (inclusive) until index 2 (exclusive)</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B-2:%5D" rel="nofollow">$..book[-2:]</a></td> 
   <td>Last two books</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B2:%5D" rel="nofollow">$..book[2:]</a></td> 
   <td>Book number two from tail</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B?%28@.isbn%29%5D" rel="nofollow">$..book[?(@.isbn)]</a></td> 
   <td>All books with an ISBN number</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$.store.book%5B?%28@.price%20%3C%2010%29%5D" rel="nofollow">$.store.book[?(@.price &lt; 10)]</a></td> 
   <td>All books in store cheaper than 10</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B?%28@.price%20%3C=%20$%5B%27expensive%27%5D%29%5D" rel="nofollow">$..book[?(@.price &lt;= $['expensive'])]</a></td> 
   <td>All books in store that are not "expensive"</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book%5B?%28@.author%20=~%20/.*REES/i%29%5D" rel="nofollow">$..book[?(@.author =~ /.*REES/i)]</a></td> 
   <td>All books matching regex (ignore case)</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..*" rel="nofollow">$..*</a></td> 
   <td>Give me every thing</td> 
  </tr> 
  <tr> 
   <td><a href="http://jsonpath.herokuapp.com/?path=$..book.length%28%29" rel="nofollow">$..book.length()</a></td> 
   <td>The number of books</td> 
  </tr> 
 </tbody> 
</table>

### Jayway JsonPath使用 ###

** 1、执行jsonPath表达式：**

String json = "...";
    
    List<String> authors = JsonPath.read(json, "$.store.book[*].author");

如果需要多次执行，避免每次读重新解析json，可以通过如下方式：

String json = "...";
    Object document = Configuration.defaultConfiguration().jsonProvider().parse(json);
    
    String author0 = JsonPath.read(document, "$.store.book[0].author");
    String author1 = JsonPath.read(document, "$.store.book[1].author");

或者：（推荐这种写法）

String json = "...";
    
    ReadContext ctx = JsonPath.parse(json);
    List<String> authorsOfBooksWithISBN = ctx.read("$.store.book[?(@.isbn)].author");

**2、返回值：**

** **JsonPath将自动尝试将结果强制转换为调用者期望的类型，如果出错将报出异常：

//Will throw an java.lang.ClassCastException    
    List<String> list = JsonPath.parse(json).read("$.store.book[0].author")
    
    //Works fine
    String author = JsonPath.parse(json).read("$.store.book[0].author")

1）当jsonPath表示为下列不确定的，则返回list：

*  .. ：全局匹配
 *  ?(<expression>) ： 过滤表达式
 *  \[<number>, <number> (, <number>)\] ：多索引

2）当表达式明确时，可以通过设置MappingProvider返回指定类型：

默认情况下，MappingProvider SPI提供了一个简单的对象映射器，当指定所需的返回类型时，MappingProvider将尝试执行映射。例如下面示例演示了Long和Date之间的映射。

String json = "{\"date_as_long\" : 1411455611975}";
    Date date = JsonPath.parse(json).read("$['date_as_long']", Date.class);

如果将JsonPath配置为使用JacksonMappingProvider或GsonMappingProvider，您甚至可以将JsonPath输出直接映射到POJO。

Configuration conf = Configuration.builder()
                                      .jsonProvider(new GsonJsonProvider())
                                      .build();
    Book book = JsonPath.using(conf).parse(json).read("$.store.book[0]", Book.class);

3）使用TypeRef：

TypeRef<List<String>> typeRef = new TypeRef<List<String>>() {};
    List<String> titles = JsonPath.parse(JSON_DOCUMENT).read("$.store.book[*].title", typeRef);

**3、配置：**

[
       {
          "name" : "john",
          "gender" : "male"
       },
       {
          "name" : "ben"
       }
    ]

1）DEFAULT\_PATH\_LEAF\_TO\_NULL：

默认JsonPath表达式在对应的json中找不到数据时会报空指针异常，配置该选项后，找不到的会返回null。

Configuration conf = Configuration.defaultConfiguration();
    
    //Works fine
    String gender0 = JsonPath.using(conf).parse(json).read("$[0]['gender']");
    //PathNotFoundException thrown
    String gender1 = JsonPath.using(conf).parse(json).read("$[1]['gender']");
    
    Configuration conf2 = conf.addOptions(Option.DEFAULT_PATH_LEAF_TO_NULL);
    
    //Works fine
    String gender0 = JsonPath.using(conf2).parse(json).read("$[0]['gender']");
    //Works fine (null is returned)
    String gender1 = JsonPath.using(conf2).parse(json).read("$[1]['gender']");

2）ALWAYS\_RETURN\_LIST：

配置后JsonPath始终返回list，即使表达式是一个明确的。

Configuration conf = Configuration.defaultConfiguration();
    
    //ClassCastException thrown
    List<String> genders0 = JsonPath.using(conf).parse(json).read("$[0]['gender']");
    
    Configuration conf2 = conf.addOptions(Option.ALWAYS_RETURN_LIST);
    
    //Works fine
    List<String> genders0 = JsonPath.using(conf2).parse(json).read("$[0]['gender']");

3）SUPPRESS\_EXCEPTIONS

默认Jayway JsonPath在执行jsonPath时会报错异常，配置后异常将被抑制。

*  如果同时指定ALWAYS\_RETURN\_LIST：返回空list；
 *  没有制定ALWAYS\_RETURN\_LIST is NOT：返回null；

4）REQUIRE\_PROPERTIES

禁止通配符，比如 $\[\*\].b，会抛出 PathNotFoundException 异常。

5）AS\_PATH\_LIST

JsonPath可以返回Path或Value。值是默认值，也是上面所有示例返回的值。可以通过该选项让其返回路径。

Configuration conf = Configuration.builder()
       .options(Option.AS_PATH_LIST).build();
    
    List<String> pathList = using(conf).parse(json).read("$..author");
    
    assertThat(pathList).containsExactly(
        "$['store']['book'][0]['author']",
        "$['store']['book'][1]['author']",
        "$['store']['book'][2]['author']",
        "$['store']['book'][3]['author']");

**4、保存/修改值：**

String newJson = JsonPath.parse(json).set("$['store']['book'][0]['author']", "Paul").jsonString();

**5、谓词（Predicates）：**

主要是filter predicate。有很多种方法实现，例如：

1）Inline Predicates

List<Map<String, Object>> books =  JsonPath.parse(json)
                                         .read("$.store.book[?(@.price < 10)]");
    
    /**
    *You can use && and || to combine multiple predicates [?(@.price < 10 && @.category == *'fiction')] , [?(@.category == 'reference' || @.price > 10)].
    *
    *You can use ! to negate a predicate [?(!(@.price < 10 && @.category == 'fiction'))].
    */

2）filter predicates：

import static com.jayway.jsonpath.JsonPath.parse;
    import static com.jayway.jsonpath.Criteria.where;
    import static com.jayway.jsonpath.Filter.filter;
    ...
    ...
    Filter cheapFictionFilter = filter(
       where("category").is("fiction").and("price").lte(10D)
    );
    List<Map<String, Object>> books =  
       parse(json).read("$.store.book[?]", cheapFictionFilter);
    
    
    //Filters can also be combined with 'OR' and 'AND'
    Filter fooOrBar = filter(
       where("foo").exists(true)).or(where("bar").exists(true)
    );
       
    Filter fooAndBar = filter(
       where("foo").exists(true)).and(where("bar").exists(true)
    );

**注**：JsonPath中的占位符？和路径中的过滤器要相互匹配。如果提供了多个过滤器，则会按占位符数量必须与提供的过滤器数量匹配的顺序应用它们。您可以在一个过滤器操作\[？，？\]中指定多个谓词占位符，两个谓词必须匹配。

3）Roll your own

Predicate booksWithISBN = new Predicate() {
        @Override
        public boolean apply(PredicateContext ctx) {
            return ctx.item(Map.class).containsKey("isbn");
        }
    };
    
    List<Map<String, Object>> books = 
       reader.read("$.store.book[?].isbn", List.class, booksWithISBN);

**6、JsonProvider SPI：**

Jayway JsonPath提供了一下json provider：

*  [JsonSmartJsonProvider][] (default)
 *  [JacksonJsonProvider][]
 *  [JacksonJsonNodeJsonProvider][JacksonJsonProvider]
 *  [GsonJsonProvider][]
 *  [JsonOrgJsonProvider][]

Configuration.setDefaults(new Configuration.Defaults() {
    
        private final JsonProvider jsonProvider = new JacksonJsonProvider();
        private final MappingProvider mappingProvider = new JacksonMappingProvider();
          
        @Override
        public JsonProvider jsonProvider() {
            return jsonProvider;
        }
    
        @Override
        public MappingProvider mappingProvider() {
            return mappingProvider;
        }
        
        @Override
        public Set<Option> options() {
            return EnumSet.noneOf(Option.class);
        }
    });

**注：**JacksonJsonProvider requires com.fasterxml.jackson.core:jackson-databind:2.4.5 and the GsonJsonProvider requires com.google.code.gson:gson:2.3.1 on your classpath.

我们在解析json时，通常也会判断值得类型是object还是array，可以使用如下方法：

Configuration conf = Configuration.builder().options(Option.AS_PATH_LIST).build();
    ReadContext ctx = JsonPath.using(conf).parse(json1_schema);
    List<String> requiredPathList = ctx.read("$..required");
    
    for (String path : requiredPathList) {
        //TODO 判断required的正确性:如果requiredValueList中元素不是array则continue
        String replace = path.replace("$['", "").replace("']['", ",").replace("']", "");
        Object object = requiredValueList.get(requiredIndex);
        requiredIndex++;
        if(object instanceof net.minidev.json.JSONArray) {
            //System.out.println("        "+replace+","+object.toString());
            pathRequiredMap.put(replace, JSONArray.parseArray(object.toString()));
        }
    }

**7、Cache SPI：**

Jayway JsonPath提供了一下cache：

*  com.jayway.jsonpath.spi.cache.LRUCache (default, thread safe)
 *  com.jayway.jsonpath.spi.cache.NOOPCache (no cache)

CacheProvider.setCache(new Cache() {
        //Not thread safe simple cache
        private Map<String, JsonPath> map = new HashMap<String, JsonPath>();
    
        @Override
        public JsonPath get(String key) {
            return map.get(key);
        }
    
        @Override
        public void put(String key, JsonPath jsonPath) {
            map.put(key, jsonPath);
        }
    });

参考：[https://zju-cy.github.io/2019/07/07/JsonPath][https_zju-cy.github.io_2019_07_07_JsonPath]

[XPath]: http://en.wikipedia.org/wiki/XPath
[Stefan Goessner JsonPath]: http://goessner.net/articles/JsonPath/
[https_github.com_json-path_JsonPath]: https://github.com/json-path/JsonPath
[http_jsonpath.herokuapp.com]: http://jsonpath.herokuapp.com/
[JsonSmartJsonProvider]: https://code.google.com/p/json-smart/
[JacksonJsonProvider]: https://github.com/FasterXML/jackson
[GsonJsonProvider]: https://code.google.com/p/google-gson/
[JsonOrgJsonProvider]: http://www.json.org/java/index.html
[https_zju-cy.github.io_2019_07_07_JsonPath]: https://zju-cy.github.io/2019/07/07/JsonPath