JsonPath实践（三）

本期讲一下获取数组时增加过滤条件，这里用到的语法稍微复杂一点点。主要的过滤条件有几类：「属性是否存在」、「属性值比较」、「属性值与属性值」和「数组长度求值」。

json数据

首先看官方给的json数据的Demo（我做了一点点修改）：

JSONObject json = JSON.parseObject("{" +
                "    "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," +
                "    "ss": [32,32,4,23]" +
                "}");

验证属性是否存在

jsonpath：$..book[?(@.isbn)]

代码：

        Object read = JsonPath.read(json, "$..book[?(@.isbn)]");
        output(JSONArray.parseArray(read.toString()));

等效写法省略……

控制台输出：

INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO-> 
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞  {
＞  ① . "author":"Herman Melville",
＞  ① . "price":8.99,
＞  ① . "isbn":"0-553-21311-3",
＞  ① . "category":"fiction",
＞  ① . "title":"Moby Dick"
＞  }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
INFO-> 
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞  {
＞  ① . "author":"J. R. R. Tolkien",
＞  ① . "price":22.99,
＞  ① . "isbn":"0-395-19395-8",
＞  ① . "category":"fiction",
＞  ① . "title":"The Lord of the Rings"
＞  }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~

Process finished with exit code 0

暂时没有找到提供验证属性不存在的API，不过这个可以通过另外的方式实现，例如：「属性值比较」和「属性值正则匹配」等等，后面会讲到。

属性值比较

字符串比较：

jsonpath：$..book[?(@.isbn == '0-395-19395-8')]

数值比较：

jsonpath：$..book[?(@.price > 20)]

这里语法支持不同数据类型的自动化转换的，跟其他脚本语言一样。JSonpath还支持更多的「值标胶」写法，这个以后单独写篇文章讲一讲。

代码：

        Object read = JsonPath.read(json, "$..book[?(@.price > 20)]");
        output(JSONArray.parseArray(read.toString()));

等效写法继续省略……

控制台输出：

INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO-> 
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞  {
＞  ① . "author":"J. R. R. Tolkien",
＞  ① . "price":22.99,
＞  ① . "isbn":"0-395-19395-8",
＞  ① . "category":"fiction",
＞  ① . "title":"The Lord of the Rings"
＞  }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~

Process finished with exit code 0

属性值与属性值

这个比较简单，涉及到一个JSonpath语法的嵌套问题。

jsonpath：..book[?(@.price >

这里语法的嵌套基本是个套娃，不过个人还是不建议使用套娃，毕竟标记语法当然是越简单越好，非常强调可读性。

代码：

        Object read = JsonPath.read(json, "$..book[?(@.price > $['expensive'])]");
        output(JSONArray.parseArray(read.toString()));

等效写法继续省略……

控制台输出：


INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO-> 
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞  {
＞  ① . "author":"Evelyn Waugh",
＞  ① . "price":12.99,
＞  ① . "category":"fiction",
＞  ① . "title":"Sword of Honour"
＞  }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
INFO-> 
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞  {
＞  ① . "author":"J. R. R. Tolkien",
＞  ① . "price":22.99,
＞  ① . "isbn":"0-395-19395-8",
＞  ① . "category":"fiction",
＞  ① . "title":"The Lord of the Rings"
＞  }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~

Process finished with exit code 0

数组长度求值

这个就更简单了，求数组长度的一个API。

jsonpath：$..book.length()

这里有一个坑，如果把length()方法用到对数组过滤或者指定数组对象之后，会变成求该对象属性个数或者过滤后数组的长度的功能了，返回结果是个数值类型的数组。

代码：

        Object read = JsonPath.read(json, "$..book.length()");
        output(read);

等效写法继续省略……

控制台输出：


INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO-> [4]

Process finished with exit code 0