Hystrix-request cache(请求缓存)

开启请求缓存

　　请求缓存在run()和construce()执行之前生效，所以可以有效减少不必要的线程开销。你可以通过实现getCachekey()方法来开启请求缓存。

package org.hope.hystrix.example.request.cache;

import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;

public class CommandUsingRequestCache extends HystrixCommand<Boolean> {
    private final int value;

    public CommandUsingRequestCache(int value) {
        super(HystrixCommandGroupKey.Factory.asKey("ExampleGroup"));
        this.value = value;
    }

    @Override
    protected Boolean run() throws Exception {
        return value == 0 || value % 2 == 0;
    }

    @Override
    protected String getCacheKey() {
        return String.valueOf(value);
    }
}

单元测试

package org.hope.hystrix.example.request.cache;

import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
import org.hope.hystrix.example.request.cache.CommandUsingRequestCache;
import org.junit.Test;

import static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

public class CommandUsingRequestCacheTest {

    @Test
    public void testWithoutCacheHits() {
        HystrixRequestContext cxt = HystrixRequestContext.initializeContext();
        try {
            assertTrue(new CommandUsingRequestCache(2).execute());
            assertTrue(new CommandUsingRequestCache(1).execute());
        } finally {
            cxt.shutdown();
        }
    }

    @Test
    public void testWithCacheHits() {
        HystrixRequestContext cxt = HystrixRequestContext.initializeContext();
        try {
            CommandUsingRequestCache command2a = new CommandUsingRequestCache(2);
            CommandUsingRequestCache command2b = new CommandUsingRequestCache(2);

            assertTrue(command2a.execute());
            // this is the first time we've executed this command with the value of "2" so it should not be from cache
//            assertFalse(command2a.isResponseFromCache());
            System.out.println(command2a.isResponseFromCache());

            assertTrue(command2b.execute());
            // this is the second time we've executed this command with the same value so it should return from cache
//            assertTrue(command2b.isResponseFromCache());
            System.out.println(command2b.isResponseFromCache());
        } finally {
            cxt.shutdown();
        }

        // start a new request context
        cxt = HystrixRequestContext.initializeContext();
        try {
            CommandUsingRequestCache command3b = new CommandUsingRequestCache(2);
            assertTrue(command3b.execute());
            // this is a new request context so this should not come from cache
//            assertFalse(command3b.isResponseFromCache());
            System.out.println(command3b.isResponseFromCache());
        } finally {
            cxt.shutdown();
        }
    }
}

清理失效缓存

package org.hope.hystrix.example.request.cache;


import com.netflix.hystrix.HystrixCommand;
import com.netflix.hystrix.HystrixCommandGroupKey;
import com.netflix.hystrix.HystrixCommandKey;
import com.netflix.hystrix.HystrixRequestCache;
import com.netflix.hystrix.strategy.concurrency.HystrixConcurrencyStrategyDefault;

/**
 * 清理缓存
 */
public class CommandUsingRequestCacheInvalidation{

    private static volatile String prefixStoredOnRemoteDataStore = "ValueBeforeSet_";

    public static class GetterCommand extends HystrixCommand<String> {
        private static final HystrixCommandKey GETTER_KEY = HystrixCommandKey.Factory.asKey("GetterCommand");
        private final int id;
        public GetterCommand(int id) {
            super(Setter.withGroupKey(HystrixCommandGroupKey.Factory.asKey("GetSetGet")).andCommandKey(GETTER_KEY));
            this.id = id;
        }

        @Override
        protected String run() throws Exception {
            return prefixStoredOnRemoteDataStore + id;
        }

        @Override
        protected String getCacheKey() {
            return String.valueOf(id);
        }

        //Allow the cache to be flushed for this object.
        public static void flushCache(int id) {
            HystrixRequestCache.getInstance(GETTER_KEY, HystrixConcurrencyStrategyDefault.getInstance()).clear(String.valueOf(id));
        }

    }

    public static class SetterCommand extends HystrixCommand<Void> {
        private final int id;
        private final String prefix;

        public SetterCommand(int id, String prefix) {
            super(HystrixCommandGroupKey.Factory.asKey("GetSetGet"));
            this.id = id;
            this.prefix = prefix;
        }


        @Override
        protected Void run() throws Exception {
            // persist the value against the datastore
            prefixStoredOnRemoteDataStore = prefix;
            // flush the cache
            GetterCommand.flushCache(id);
            return null;
        }
    }

}

单元测试：

package org.hope.hystrix.example.request.cache;

import com.netflix.hystrix.strategy.concurrency.HystrixRequestContext;
import org.junit.Test;

/**
 * Created by lisen on 2017/12/27.
 */
public class CommandUsingRequestCacheInvalidationTest {

    @Test
    public void flushCacheTest() {
        HystrixRequestContext context = HystrixRequestContext.initializeContext();
        System.out.println(new CommandUsingRequestCacheInvalidation.GetterCommand(1).execute());

        CommandUsingRequestCacheInvalidation.GetterCommand commandAgainstCache = new CommandUsingRequestCacheInvalidation.GetterCommand(1);

        System.out.println(commandAgainstCache.isResponseFromCache()); //false
        System.out.println(commandAgainstCache.execute());
        System.out.println(commandAgainstCache.isResponseFromCache()); //false
        // set the new value
        new CommandUsingRequestCacheInvalidation.SetterCommand(1, "ValueAfterSet_").execute();
        // fetch it again
        CommandUsingRequestCacheInvalidation.GetterCommand commandAfterSet = new CommandUsingRequestCacheInvalidation.GetterCommand(1);
        //the getter should return with the new prefix, not the value from cache
        System.out.println(commandAfterSet.isResponseFromCache());
        System.out.println(commandAfterSet.execute());
    }
}

注解的实现请求缓存

注解	描述	属性
@CacheResult	改注解用来标记请求命令返回的结果应该被缓存，它必须与@HystrixCommand注解结合使用	cacheKeyMethod
@CacheRemove	该注解用来让请求命令的缓存失效，失效的缓存根据定义的key决定	commandKey,cacheKeyMethod
@CacheKey	改注解用来在请求命令的参数上标记，使其作为缓存的Key值，如果没有标注则会使用所有参数。如果同时还使用了@CacheResult和 @CacheRemove注解的cacheKeyMethod方法指定缓存Key的生成，那么该注解将不会起作用	value

设置缓存

package org.hope.hystrix.example.request.cache;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheKey;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheResult;
import org.hope.hystrix.example.model.User;
import org.springframework.stereotype.Service;

@Service
public class RequestCacheAnnotation {

    /**
     *  返回的结果会置入请求缓存中，缓存的key值会使用所有的方法入参，
     *  也就是这里Long类型的id
     */
    @CacheResult
    @HystrixCommand
    public String getUserById(Long id) {
        return "你好" + id;
    }

    /**
     *  cacheKeyMethod可以为缓存指定具体的缓存key
     */
    @CacheResult(cacheKeyMethod = "getUserByIdCacheKey")
    @HystrixCommand
    public String getUserById2(Long id) {
        return "你好:" + id;
    }

    public String getUserByIdCacheKey(Long id) {
        return String.valueOf(id);
    }

    /**
     *  通过@CacheKey来定义具体的缓存Key。
     *  但是注意，@CacheKey的优先级比@CacheResult(cacheKeyMethod = "")的优先级低。
     *  如果已经使用了cacheKeyMethod指定缓存Key的生成函数，那么@CacheKey注解不会生效
     */
    @CacheResult
    @HystrixCommand
    public String getUserById3(@CacheKey("id") Long id) {
        return "你好:" + id;
    }

    /**
     *  @CacheKey还可以通过访问参数对象内部属性作为缓存key
     *  这里指定了User对象id属性作为缓存key
     */
    @CacheResult
    @HystrixCommand
    public String getUserById4(@CacheKey("id") User user) {
        return "你好" + user.getId();
    }

}

清理缓存

package org.hope.hystrix.example.request.cache;

import com.netflix.hystrix.contrib.javanica.annotation.HystrixCommand;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheKey;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheRemove;
import com.netflix.hystrix.contrib.javanica.cache.annotation.CacheResult;
import org.hope.hystrix.example.model.User;

public class RequestClearCacheAnnotation {

    @CacheResult
    @HystrixCommand
    public User getUserById(@CacheKey("id") Long id) {
        User u = new User();
        u.setId(id);
        return u;
    }

    /**
     * 用@CacheRemove来清理失效缓存，其中commandKey是必须指定的
     */
    @CacheRemove(commandKey = "getUserById")
    @HystrixCommand
    public void update(@CacheKey("id") User user) {
        User u = new User();
        u.setId(20L);
    }

    public String getUserById(User user) {
        return String.valueOf(user.getId());
    }
}

https://gitee.com/huayicompany/Hystrix-learn/tree/master/hystrix-example

参考：

[1]Github，https://github.com/Netflix/Hystrix/wiki/How-it-Works

[2] 《SpringCloud微服务实战》，电子工业出版社，翟永超