3,JsonPath进阶实战--断言

断言

断言简单点说就是满足一定条件的逻辑表达式.在Springboot Cloud Gateway中匹配路由的断言及Java8中提供的Predicate接口都是断言.

JsonPath中有三种方式创建断言: 行内断言, 过滤器断言, 自定义断言

准备json数据

{
    "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
}

Book实体

@Data  
public static class Book {  
  
    /**  
     * 分类  
     */  
    private String category;  
    /**  
     * 作者  
     */  
    private String author;  
    /**  
     * 标题  
     */  
    private String title;  
    /**  
     * 价格  
     */  
    private Double price;  
  
    /**  
     * 书籍编号  
     */  
    private String isbn;  
}

maven坐标

<dependency>  
    <groupId>org.projectlombok</groupId>  
    <artifactId>lombok</artifactId>  
    <version>1.18.16</version>  
</dependency>

<dependency>  
   <groupId>cn.hutool</groupId>  
   <artifactId>hutool-all</artifactId>  
   <version>5.3.9</version>  
</dependency>

<dependency>
    <groupId>com.jayway.jsonpath</groupId>
    <artifactId>json-path</artifactId>
    <version>2.7.0</version>
</dependency>

0,通过三种断言实现抽取book对象包含isbn属性同时price属性的值要大于10

1,行内断言

行内断言定义在计算路径中

TypeRef<List<Book>> typeRef = new TypeRef<List<Book>>(){};  
// 行内断言  
List<Book> books = JsonPath.parse(jsonData).read("$..book[?(@.isbn && @.price > 10)]", typeRef);
Console.log(JSONUtil.toJsonStr(books));

可以使用&& 和 ||组合多种断言,比如[?(@.price < 10 && @.category == 'fiction')] , [?(@.category == 'reference' || @.price > 10)],[?(!(@.price < 10 && @.category == 'fiction'))].

2,过滤器断言

使用Filter API构建断言

• 方式1

// 过滤器断言 1
Filter filter = Filter.filter(Criteria.where("isbn").exists(true).and("price").gt(10));
List<Book> books = JsonPath.parse(jsonData).read("$..book[?]", filter);
Console.log(JSONUtil.toJsonStr(books));

• 方式2

// 过滤器断言 2
Filter filter = Filter.filter(Criteria.where("isbn").exists(true)).and(Criteria.where("price").gt(10));
List<Book> books = JsonPath.parse(jsonData).read("$..book[?]", filter);
Console.log(JSONUtil.toJsonStr(books));

• 方式3

// 过滤器断言 3
Filter filter1 = Filter.filter(Criteria.where("isbn").exists(true));
Filter filter2 = Filter.filter(Criteria.where("price").gt(10));
List<Book> books = JsonPath.parse(jsonData).read("$..book[?][?]", filter1,filter2);
Console.log(JSONUtil.toJsonStr(books));

注意路径中的过滤器占位符?, 其中占位符的数量要和过滤器的数量一致

3,自定义断言

// 自定义断言
Predicate booksWithISBNAndPrice = ctx -> ctx.item(Map.class).containsKey("isbn") && (Double)ctx.item(Map.class).get("price") > 10;
List<Book> books = JsonPath.read(document,"$..book[?]", booksWithISBNAndPrice);
Console.log(JSONUtil.toJsonStr(books));

20220721013253.png

总结:

• 以上3种方式的断言使用方法都可以相互转换
• 行内断言和过滤器断言使用方便灵活
• 自定义断言灵活但是不好理解和编写