緩存是實際工作中非常常用的一種提高性能的方法, 我們會在許多場景下來使用緩存。
本文通過一個簡單的例子進行展開,通過對比我們原來的自定義緩存和 spring 的基於註釋的 cache 配置方法,展現了 spring cache 的強大之處,然後介紹了其基本的原理,擴展點和使用場景的限制。通過閱讀本文,你應該可以短時間內掌握 spring 帶來的強大緩存技術,在很少的配置下即可給既有代碼提供緩存能力。
概述
Spring 3.1 引入了激動人心的基於註釋(annotation)的緩存(cache)技術,它本質上不是一個具體的緩存實現方案(例如EHCache 或者 OSCache),而是一個對緩存使用的抽象,通過在既有代碼中添加少量它定義的各種 annotation,即能夠達到緩存方法的返回對象的效果。
Spring 的緩存技術還具備相當的靈活性,不僅能夠使用 SpEL(Spring Expression Language)來定義緩存的 key 和各種 condition,還提供開箱即用的緩存臨時存儲方案,也支持和主流的專業緩存例如 EHCache 集成。
其特點總結如下:
-
通過少量的配置 annotation 註釋即可使得既有代碼支持緩存
-
支持開箱即用 Out-Of-The-Box,即不用安裝和部署額外第三方組件即可使用緩存
-
支持 Spring Express Language,能使用對象的任何屬性或者方法來定義緩存的 key 和 condition
-
支持 AspectJ,並通過其實現任何方法的緩存支持
-
支持自定義 key 和自定義緩存管理者,具有相當的靈活性和擴展性
本文將針對上述特點對 Spring cache 進行詳細的介紹,主要通過一個簡單的例子和原理介紹展開,然後我們將一起看一個比較實際的緩存例子,最後會介紹 spring cache 的使用限制和注意事項。好吧,讓我們開始吧
我們以前如何自己實現緩存的呢
這裏先展示一個完全自定義的緩存實現,即不用任何第三方的組件來實現某種對象的內存緩存。
場景如下:
對一個賬號查詢方法做緩存,以賬號名稱爲 key,賬號對象爲 value,當以相同的賬號名稱查詢賬號的時候,直接從緩存中返回結果,否則更新緩存。賬號查詢服務還支持 reload 緩存(即清空緩存)
首先定義一個實體類:賬號類,具備基本的 id 和 name 屬性,且具備 getter 和 setter 方法
- public class Account {
- private int id;
- private String name;
- public Account(String name) {
- this.name = name;
- }
- public int getId() {
- return id;
- }
- public void setId(int id) {
- this.id = id;
- }
- public String getName() {
- return name;
- }
- public void setName(String name) {
- this.name = name;
- }
- }
public class Account {
private int id;
private String name;
public Account(String name) {
this.name = name;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
然後定義一個緩存管理器,這個管理器負責實現緩存邏輯,支持對象的增加、修改和刪除,支持值對象的泛型。如下:
- import com.google.common.collect.Maps;
- import java.util.Map;
- /**
- * @author wenchao.ren
- * 2015/1/5.
- */
- public class CacheContext<T> {
- private Map<String, T> cache = Maps.newConcurrentMap();
- public T get(String key){
- return cache.get(key);
- }
- public void addOrUpdateCache(String key,T value) {
- cache.put(key, value);
- }
- // 根據 key 來刪除緩存中的一條記錄
- public void evictCache(String key) {
- if(cache.containsKey(key)) {
- cache.remove(key);
- }
- }
- // 清空緩存中的所有記錄
- public void evictCache() {
- cache.clear();
- }
- }
import com.google.common.collect.Maps;
import java.util.Map;
/**
* @author wenchao.ren
* 2015/1/5.
*/
public class CacheContext<T> {
private Map<String, T> cache = Maps.newConcurrentMap();
public T get(String key){
return cache.get(key);
}
public void addOrUpdateCache(String key,T value) {
cache.put(key, value);
}
// 根據 key 來刪除緩存中的一條記錄
public void evictCache(String key) {
if(cache.containsKey(key)) {
cache.remove(key);
}
}
// 清空緩存中的所有記錄
public void evictCache() {
cache.clear();
}
}
好,現在我們有了實體類和一個緩存管理器,還需要一個提供賬號查詢的服務類,此服務類使用緩存管理器來支持賬號查詢緩存,如下:
- import com.google.common.base.Optional;
- import org.slf4j.Logger;
- import org.slf4j.LoggerFactory;
- import org.springframework.stereotype.Service;
- import javax.annotation.Resource;
- /**
- * @author wenchao.ren
- * 2015/1/5.
- */
- @Service
- public class AccountService1 {
- private final Logger logger = LoggerFactory.getLogger(AccountService1.class);
- @Resource
- private CacheContext<Account> accountCacheContext;
- public Account getAccountByName(String accountName) {
- Account result = accountCacheContext.get(accountName);
- if (result != null) {
- logger.info("get from cache... {}", accountName);
- return result;
- }
- Optional<Account> accountOptional = getFromDB(accountName);
- if (!accountOptional.isPresent()) {
- throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
- }
- Account account = accountOptional.get();
- accountCacheContext.addOrUpdateCache(accountName, account);
- return account;
- }
- public void reload() {
- accountCacheContext.evictCache();
- }
- private Optional<Account> getFromDB(String accountName) {
- logger.info("real querying db... {}", accountName);
- //Todo query data from database
- return Optional.fromNullable(new Account(accountName));
- }
- }
import com.google.common.base.Optional;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Service;
import javax.annotation.Resource;
/**
* @author wenchao.ren
* 2015/1/5.
*/
@Service
public class AccountService1 {
private final Logger logger = LoggerFactory.getLogger(AccountService1.class);
@Resource
private CacheContext<Account> accountCacheContext;
public Account getAccountByName(String accountName) {
Account result = accountCacheContext.get(accountName);
if (result != null) {
logger.info("get from cache... {}", accountName);
return result;
}
Optional<Account> accountOptional = getFromDB(accountName);
if (!accountOptional.isPresent()) {
throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
}
Account account = accountOptional.get();
accountCacheContext.addOrUpdateCache(accountName, account);
return account;
}
public void reload() {
accountCacheContext.evictCache();
}
private Optional<Account> getFromDB(String accountName) {
logger.info("real querying db... {}", accountName);
//Todo query data from database
return Optional.fromNullable(new Account(accountName));
}
}
現在我們開始寫一個測試類,用於測試剛纔的緩存是否有效
- import org.junit.Before;
- import org.junit.Test;
- import org.slf4j.Logger;
- import org.slf4j.LoggerFactory;
- import org.springframework.context.support.ClassPathXmlApplicationContext;
- import static org.junit.Assert.*;
- public class AccountService1Test {
- private AccountService1 accountService1;
- private final Logger logger = LoggerFactory.getLogger(AccountService1Test.class);
- @Before
- public void setUp() throws Exception {
- ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext1.xml");
- accountService1 = context.getBean("accountService1", AccountService1.class);
- }
- @Test
- public void testInject(){
- assertNotNull(accountService1);
- }
- @Test
- public void testGetAccountByName() throws Exception {
- accountService1.getAccountByName("accountName");
- accountService1.getAccountByName("accountName");
- accountService1.reload();
- logger.info("after reload ....");
- accountService1.getAccountByName("accountName");
- accountService1.getAccountByName("accountName");
- }
- }
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import static org.junit.Assert.*;
public class AccountService1Test {
private AccountService1 accountService1;
private final Logger logger = LoggerFactory.getLogger(AccountService1Test.class);
@Before
public void setUp() throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext1.xml");
accountService1 = context.getBean("accountService1", AccountService1.class);
}
@Test
public void testInject(){
assertNotNull(accountService1);
}
@Test
public void testGetAccountByName() throws Exception {
accountService1.getAccountByName("accountName");
accountService1.getAccountByName("accountName");
accountService1.reload();
logger.info("after reload ....");
accountService1.getAccountByName("accountName");
accountService1.getAccountByName("accountName");
}
}
按照分析,執行結果應該是:首先從數據庫查詢,然後直接返回緩存中的結果,重置緩存後,應該先從數據庫查詢,然後返回緩存中的結果. 查看程序運行的日誌如下:
00:53:17.166 [main] INFO c.r.s.cache.example1.AccountService - real querying db... accountName
00:53:17.168 [main] INFO c.r.s.cache.example1.AccountService - get from cache... accountName
00:53:17.168 [main] INFO c.r.s.c.example1.AccountServiceTest - after reload ....
00:53:17.168 [main] INFO c.r.s.cache.example1.AccountService - real querying db... accountName
00:53:17.169 [main] INFO c.r.s.cache.example1.AccountService - get from cache... accountName
可以看出我們的緩存起效了,但是這種自定義的緩存方案有如下劣勢:
-
緩存代碼和業務代碼耦合度太高,如上面的例子,AccountService 中的 getAccountByName()方法中有了太多緩存的邏輯,不便於維護和變更
-
不靈活,這種緩存方案不支持按照某種條件的緩存,比如只有某種類型的賬號才需要緩存,這種需求會導致代碼的變更
-
緩存的存儲這塊寫的比較死,不能靈活的切換爲使用第三方的緩存模塊
如果你的代碼中有上述代碼的影子,那麼你可以考慮按照下面的介紹來優化一下你的代碼結構了,也可以說是簡化,你會發現,你的代碼會變得優雅的多!
Spring cache是如何做的呢
我們對AccountService1 進行修改,創建AccountService2:
- import com.google.common.base.Optional;
- import com.rollenholt.spring.cache.example1.Account;
- import org.slf4j.Logger;
- import org.slf4j.LoggerFactory;
- import org.springframework.cache.annotation.Cacheable;
- import org.springframework.stereotype.Service;
- /**
- * @author wenchao.ren
- * 2015/1/5.
- */
- @Service
- public class AccountService2 {
- private final Logger logger = LoggerFactory.getLogger(AccountService2.class);
- // 使用了一個緩存名叫 accountCache
- @Cacheable(value="accountCache")
- public Account getAccountByName(String accountName) {
- // 方法內部實現不考慮緩存邏輯,直接實現業務
- logger.info("real querying account... {}", accountName);
- Optional<Account> accountOptional = getFromDB(accountName);
- if (!accountOptional.isPresent()) {
- throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
- }
- return accountOptional.get();
- }
- private Optional<Account> getFromDB(String accountName) {
- logger.info("real querying db... {}", accountName);
- //Todo query data from database
- return Optional.fromNullable(new Account(accountName));
- }
- }
import com.google.common.base.Optional;
import com.rollenholt.spring.cache.example1.Account;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.cache.annotation.Cacheable;
import org.springframework.stereotype.Service;
/**
* @author wenchao.ren
* 2015/1/5.
*/
@Service
public class AccountService2 {
private final Logger logger = LoggerFactory.getLogger(AccountService2.class);
// 使用了一個緩存名叫 accountCache
@Cacheable(value="accountCache")
public Account getAccountByName(String accountName) {
// 方法內部實現不考慮緩存邏輯,直接實現業務
logger.info("real querying account... {}", accountName);
Optional<Account> accountOptional = getFromDB(accountName);
if (!accountOptional.isPresent()) {
throw new IllegalStateException(String.format("can not find account by account name : [%s]", accountName));
}
return accountOptional.get();
}
private Optional<Account> getFromDB(String accountName) {
logger.info("real querying db... {}", accountName);
//Todo query data from database
return Optional.fromNullable(new Account(accountName));
}
}
我們注意到在上面的代碼中有一行:
@Cacheable(value="accountCache")
這個註釋的意思是,當調用這個方法的時候,會從一個名叫 accountCache 的緩存中查詢,如果沒有,則執行實際的方法(即查詢數據庫),並將執行的結果存入緩存中,否則返回緩存中的對象。這裏的緩存中的 key 就是參數 accountName,value 就是 Account 對象。“accountCache”緩存是在 spring*.xml 中定義的名稱。我們還需要一個 spring 的配置文件來支持基於註釋的緩存
- <beans xmlns="http://www.springframework.org/schema/beans"
- xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
- xmlns:context="http://www.springframework.org/schema/context"
- xmlns:cache="http://www.springframework.org/schema/cache"
- xsi:schemaLocation="http://www.springframework.org/schema/beans
- http://www.springframework.org/schema/beans/spring-beans.xsd
- http://www.springframework.org/schema/context
- http://www.springframework.org/schema/context/spring-context.xsd
- http://www.springframework.org/schema/cache
- http://www.springframework.org/schema/cache/spring-cache.xsd">
- <context:component-scan base-package="com.rollenholt.spring.cache"/>
- <context:annotation-config/>
- <cache:annotation-driven/>
- <bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
- <property name="caches">
- <set>
- <bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean">
- <property name="name" value="default"/>
- </bean>
- <bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean">
- <property name="name" value="accountCache"/>
- </bean>
- </set>
- </property>
- </bean>
- </beans>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:cache="http://www.springframework.org/schema/cache"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/cache
http://www.springframework.org/schema/cache/spring-cache.xsd">
<context:component-scan base-package="com.rollenholt.spring.cache"/>
<context:annotation-config/>
<cache:annotation-driven/>
<bean id="cacheManager" class="org.springframework.cache.support.SimpleCacheManager">
<property name="caches">
<set>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean">
<property name="name" value="default"/>
</bean>
<bean class="org.springframework.cache.concurrent.ConcurrentMapCacheFactoryBean">
<property name="name" value="accountCache"/>
</bean>
</set>
</property>
</bean>
</beans>
注意這個 spring 配置文件有一個關鍵的支持緩存的配置項:
<cache:annotation-driven />
這個配置項缺省使用了一個名字叫 cacheManager 的緩存管理器,這個緩存管理器有一個 spring 的缺省實現,即 org.springframework.cache.support.SimpleCacheManager,這個緩存管理器實現了我們剛剛自定義的緩存管理器的邏輯,它需要配置一個屬性 caches,即此緩存管理器管理的緩存集合,除了缺省的名字叫 default 的緩存,我們還自定義了一個名字叫 accountCache 的緩存,使用了缺省的內存存儲方案 ConcurrentMapCacheFactoryBean,它是基於 Java.util.concurrent.ConcurrentHashMap 的一個內存緩存實現方案。
然後我們編寫測試程序:
- import org.junit.Before;
- import org.junit.Test;
- import org.slf4j.Logger;
- import org.slf4j.LoggerFactory;
- import org.springframework.context.support.ClassPathXmlApplicationContext;
- import static org.junit.Assert.*;
- public class AccountService2Test {
- private AccountService2 accountService2;
- private final Logger logger = LoggerFactory.getLogger(AccountService2Test.class);
- @Before
- public void setUp() throws Exception {
- ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext2.xml");
- accountService2 = context.getBean("accountService2", AccountService2.class);
- }
- @Test
- public void testInject(){
- assertNotNull(accountService2);
- }
- @Test
- public void testGetAccountByName() throws Exception {
- logger.info("first query...");
- accountService2.getAccountByName("accountName");
- logger.info("second query...");
- accountService2.getAccountByName("accountName");
- }
- }
import org.junit.Before;
import org.junit.Test;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import static org.junit.Assert.*;
public class AccountService2Test {
private AccountService2 accountService2;
private final Logger logger = LoggerFactory.getLogger(AccountService2Test.class);
@Before
public void setUp() throws Exception {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("applicationContext2.xml");
accountService2 = context.getBean("accountService2", AccountService2.class);
}
@Test
public void testInject(){
assertNotNull(accountService2);
}
@Test
public void testGetAccountByName() throws Exception {
logger.info("first query...");
accountService2.getAccountByName("accountName");
logger.info("second query...");
accountService2.getAccountByName("accountName");
}
}
上面的測試代碼主要進行了兩次查詢,第一次應該會查詢數據庫,第二次應該返回緩存,不再查數據庫,我們執行一下,看看結果
01:10:32.435 [main] INFO c.r.s.c.example2.AccountService2Test - first query...
01:10:32.456 [main] INFO c.r.s.cache.example2.AccountService2 - real querying account... accountName
01:10:32.457 [main] INFO c.r.s.cache.example2.AccountService2 - real querying db... accountName
01:10:32.458 [main] INFO c.r.s.c.example2.AccountService2Test - second query...
可以看出我們設置的基於註釋的緩存起作用了,而在 AccountService.java 的代碼中,我們沒有看到任何的緩存邏輯代碼,只有一行註釋:@Cacheable(value=”accountCache”),就實現了基本的緩存方案,是不是很強大?
轉載自:http://blog.csdn.net/a494303877/article/details/53780597