JsonPath Cache SPI

JsonPath 2.1.0 引入了新的缓存 SPI。这允许 API 用户根据自己的需要配置路径缓存。缓存必须在首次访问前配置好，否则会产生 JsonPathException 异常。JsonPath 有两种缓存实现

• com.jayway.jsonpath.spi.cache.LRUCache （默认，线程安全）

• com.jayway.jsonpath.spi.cache.NOOPCache （无缓存）

如果您想实现自己的缓存，API 也很简单，例如：

CacheProvider.setCache(new Cache() {
    // 简单缓存，不是线程安全的
    private Map<String, JsonPath> map = new HashMap<String, JsonPath>();

    // 从缓存中获取
    @Override
    public JsonPath get(String key) {
        return map.get(key);
    }

    // 设置值到缓存
    @Override
    public void put(String key, JsonPath jsonPath) {
        map.put(key, jsonPath);
    }
});

下面是一个完整示例：

package com.hxstrive.json_path;

import com.jayway.jsonpath.JsonPath;
import com.jayway.jsonpath.spi.cache.Cache;
import com.jayway.jsonpath.spi.cache.CacheProvider;

import java.util.List;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;

/**
 * Jayway JsonPath 示例
 * @author hxstrive.com
 */
public class Demo15 {

    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" +
                "}";

        // 自定义缓存
        CacheProvider.setCache(new Cache() {
            private Map<String, JsonPath> map = new ConcurrentHashMap<String, JsonPath>();

            @Override
            public JsonPath get(String key) {
                System.out.println(">> 从缓存获取 key");
                return map.get(key);
            }

            @Override
            public void put(String key, JsonPath jsonPath) {
                System.out.println("<< " + key + " 放入缓存");
                map.put(key, jsonPath);
            }
        });

        String color = JsonPath.read(json, "$.store.bicycle.color");
        System.out.println("color=" + color);

        color = JsonPath.read(json, "$.store.bicycle.color");
        System.out.println("color=" + color);
    }

}

运行示例，输出如下：

>> 从缓存获取 key
<< $.store.bicycle.color 放入缓存
color=red
>> 从缓存获取 key
color=red

从输出可知，首次访问时缓存没有命中，且进行了缓存设置操作，第二次访问时，缓存命中了。