JsonPath index() 函数：获取指定下标的元素

在 Jayway JSONPath 中，index() 函数用于获取数组中指定下标的元素，如果下标为负数，则从数组末尾开始获取。如下：

[0, 1, 2, 3, 4, 5]

[-5, -4, -3, -2, -1]

假设我们有以下 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
}

如果执行 $.store.book.index(2) 表达式将获取下标为 2 的书籍，JSON 如下：

{
    "category": "fiction",
    "author": "Herman Melville",
    "title": "Moby Dick",
    "isbn": "0-553-21311-3",
    "price": 8.99
}

如果执行 $.store.book.index(-1) 表达式将获取最后一本书籍，JSON 如下：

{
    "category": "fiction",
    "author": "J. R. R. Tolkien",
    "title": "The Lord of the Rings",
    "isbn": "0-395-19395-8",
    "price": 22.99
}

Java 示例：

package com.hxstrive.json_path.function;

import com.jayway.jsonpath.JsonPath;

/**
 * last() 函数
 * @author hxstrive.com
 */
public class FunctionDemo10 {

    public static void main(String[] args) {
        String json = "{" +
                "    \"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" +
                "}";
        Object obj = JsonPath.read(json, "$.store.book.last()");
        System.out.println(obj);
    }

}

运行示例，输出如下：

{category=fiction, author=J. R. R. Tolkien, title=The Lord of the Rings, isbn=0-395-19395-8, price=22.99}