apache httpclient cache 实现可缓存的http客户端

这里的cache storage 采用ehcache，而不是默认的内存式的cache storage。采用ehcache可以将内容缓存到磁盘上。

maven

        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient</artifactId>
            <version>4.5</version>
        </dependency>

        <dependency>
            <groupId>org.apache.httpcomponents</groupId>
            <artifactId>httpclient-cache</artifactId>
            <version>4.5</version>
        </dependency>


        <dependency>
            <groupId>net.sf.ehcache</groupId>
            <artifactId>ehcache</artifactId>
            <version>2.8.3</version>
        </dependency>

ehcache配置如下：

<ehcache>
    <!-- <diskStore path="java.io.tmpdir" /> -->
    
    <diskStore path="c:\ehcache"/>
    
    <defaultCache 
        maxElementsInMemory="10000" 
        eternal="false"
        timeToIdleSeconds="120" 
        timeToLiveSeconds="120" 
        overflowToDisk="true"
        maxElementsOnDisk="10000000" 
        diskPersistent="false"
        diskExpiryThreadIntervalSeconds="120" 
        memoryStoreEvictionPolicy="LRU" />


    <cache name="httpCache" 
        maxElementsInMemory="10000" 
        eternal="true"
        timeToIdleSeconds="0" 
        timeToLiveSeconds="0"  
        overflowToDisk="true"
        maxElementsOnDisk="10000000" 
        diskPersistent="true"
        diskExpiryThreadIntervalSeconds="120" 
        memoryStoreEvictionPolicy="LRU" />
</ehcache>

这里有两个关键点：一是将eternal设置为true，表示采用非内存式的缓存；二是将diskPersistent设置为true，表示将缓存持久化到硬盘。

测试的代码如下：

package my.httpClient;

import java.io.IOException;

import net.sf.ehcache.Cache;
import net.sf.ehcache.CacheManager;
import net.sf.ehcache.config.CacheConfiguration;
import net.sf.ehcache.config.Configuration;
import net.sf.ehcache.config.DiskStoreConfiguration;
import net.sf.ehcache.config.PersistenceConfiguration;
import net.sf.ehcache.config.PersistenceConfiguration.Strategy;
import net.sf.ehcache.store.MemoryStoreEvictionPolicy;

import org.apache.http.HttpHost;
import org.apache.http.client.ClientProtocolException;
import org.apache.http.client.cache.CacheResponseStatus;
import org.apache.http.client.cache.HttpCacheContext;
import org.apache.http.client.config.RequestConfig;
import org.apache.http.client.methods.CloseableHttpResponse;
import org.apache.http.client.methods.HttpGet;
import org.apache.http.impl.client.CloseableHttpClient;
import org.apache.http.impl.client.cache.CacheConfig;
import org.apache.http.impl.client.cache.CachingHttpClients;
import org.apache.http.impl.client.cache.ehcache.EhcacheHttpCacheStorage;

public class EhCacheTest1 {

    public static void main(String[] args) throws ClientProtocolException,
            IOException {

        System.out.println("begin");

        // EhCache缓存存储
        CacheManager cacheManager = CacheManager.create();
        Cache httpCache = cacheManager.getCache("httpCache");

        // 定义httpclient的缓存存储
        EhcacheHttpCacheStorage ehcacheHttpCacheStorage = new EhcacheHttpCacheStorage(
                httpCache);

        // 缓存配置
        CacheConfig cacheConfig = CacheConfig.custom()
                .setMaxCacheEntries(10000).setMaxObjectSize(819200).build();

        RequestConfig requestConfig = RequestConfig.custom()
                .setConnectTimeout(30000).setSocketTimeout(30000).build();

        HttpHost proxy = new HttpHost("127.0.0.1", 8888);

        CloseableHttpClient cachingClient = CachingHttpClients.custom()
                .setCacheConfig(cacheConfig)
                .setHttpCacheStorage(ehcacheHttpCacheStorage)
                .setDefaultRequestConfig(requestConfig).setProxy(proxy).build();

        HttpCacheContext context = HttpCacheContext.create();
        HttpGet httpget = new HttpGet("http://test.cn:11677/api/values?id=8888");

        CloseableHttpResponse response = cachingClient
                .execute(httpget, context);
        try {
            CacheResponseStatus responseStatus = context
                    .getCacheResponseStatus();
            switch (responseStatus) {
            case CACHE_HIT:
                System.out
                        .println("A response was generated from the cache with "
                                + "no requests sent upstream");
                break;
            case CACHE_MODULE_RESPONSE:
                System.out
                        .println("The response was generated directly by the "
                                + "caching module");
                break;
            case CACHE_MISS:
                System.out.println("The response came from an upstream server");
                break;
            case VALIDATED:
                System.out.println("The response was generated from the cache "
                        + "after validating the entry with the origin server");
                break;
            }
        } catch (Exception e) {
            // TODO: handle exception

        } finally {
             response.close();
             cacheManager.shutdown();        
             System.out.println("end");
        }
    }

}

以上代码有几个需要说明的地方：

（1）服务端需要遵循RFC2626中规定缓存方面的协议。

（2）代码setHttpCacheStorage(ehcacheHttpCacheStorage)用于设置缓存存储。

（3）代码setProxy(proxy)用于配置代理，当你使用fiddler进行调试的时候，这个很有用。若不采用代理，则可以将这句给去掉。

（4）代码cacheManager.shutdown()用于关闭cacheManager，记得一定要执行这一句，否则会报错。