书接上文和上上文：
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。
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]" +
"}");
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
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。字符串比较：
jsonpath：$..book[?(@.isbn == '0-395-19395-8')]
数值比较：
jsonpath：$..book[?(@.price > 20)]
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, "$..book[?(@.price > 20)]");
output(JSONArray.parseArray(read.toString()));
等效写法继续省略……
控制台输出：
INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO->
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞ {
＞ ① . "author":"J. R. R. Tolkien",
＞ ① . "price":22.99,
＞ ① . "isbn":"0-395-19395-8",
＞ ① . "category":"fiction",
＞ ① . "title":"The Lord of the Rings"
＞ }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
Process finished with exit code 0
这个比较简单，涉及到一个JSonpath语法的嵌套问题。
jsonpath：$..book[?(@.price > $['expensive'])]
代码：
Object read = JsonPath.read(json, "$..book[?(@.price > $['expensive'])]");
output(JSONArray.parseArray(read.toString()));
等效写法继续省略……
控制台输出：
INFO-> 当前用户：fv，IP：10.60.192.21，工作目录：/Users/fv/Documents/workspace/fun/,系统编码格式:UTF-8,系统Mac OS X版本:10.15.6
INFO->
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞ {
＞ ① . "author":"Evelyn Waugh",
＞ ① . "price":12.99,
＞ ① . "category":"fiction",
＞ ① . "title":"Sword of Honour"
＞ }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
INFO->
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
＞ {
＞ ① . "author":"J. R. R. Tolkien",
＞ ① . "price":22.99,
＞ ① . "isbn":"0-395-19395-8",
＞ ① . "category":"fiction",
＞ ① . "title":"The Lord of the Rings"
＞ }
~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~ JSON ~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~~☢~
Process finished with exit code 0
这个就更简单了，求数组长度的一个API。
jsonpath：$..book.length()
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