在Mybatis中允许开发者自定义自己的缓存，本文将使用Redis作为Mybatis的二级缓存。在Mybatis中定义二级缓存，需要如下配置：
1、 MyBatis支持二级缓存的总开关：全局配置变量参数“cacheEnabled=true”
2、select语句所在的Mapper需配置了<cache> 或<cached-ref>节点
3、select语句的参数 useCache=true
Mybatis配置文件如下：
<settings>
<!-- 这个配置使全局的映射器启用或禁用缓存 -->
<setting name="cacheEnabled" value="true" />
<!-- 对于未知的SQL查询，允许返回不同的结果集以达到通用的效果 -->
<setting name="multipleResultSetsEnabled" value="true"/>
<!-- 配置默认的执行器。SIMPLE 执行器没有什么特别之处。REUSE 执行器重用预处理语句。BATCH 执行器重用语句和批量更新 -->
<setting name="defaultExecutorType" value="REUSE" />
<!-- 全局启用或禁用延迟加载。当禁用时，所有关联对象都会即时加载。 -->
<setting name="lazyLoadingEnabled" value="false" />
<setting name="aggressiveLazyLoading" value="true" />
<!-- <setting name="enhancementEnabled" value="true"/> -->
<!-- 设置超时时间，它决定驱动等待一个数据库响应的时间。 -->
<setting name="defaultStatementTimeout" value="25000" />
</settings>
Mybatis的Mapper的配置文件如下：
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="user"> <!-- 二级缓存 -->
<cache type="com.qunar.mobile.mybatis.cache.QRedisCache"/> <select id="getUsers" resultType="User" useCache="true">
select
user_id as userId, user_name as username, user_desc as userDesc, create_time as createTime
from bisystem_user
</select> </mapper>
自定义二级缓存需要实现Mybatis的Cache接口，Redis缓存实现如下：
public class QRedisCache implements Cache {
private String cacheId;
private final ReadWriteLock readWriteLock = new ReentrantReadWriteLock(true);
public QRedisCache(String cacheId) {
if (cacheId == null) {
throw new IllegalArgumentException("Cache instances require an ID");
}
this.cacheId = cacheId;
}
@Override
public String getId() {
return cacheId;
}
@Override
public void putObject(Object key, Object value) {
JedisUtils.put(key, value);
}
@Override
public Object getObject(Object key) {
return JedisUtils.get(key);
}
@Override
public Object removeObject(Object key) {
return JedisUtils.remove(key);
}
@Override
public void clear() {
JedisUtils.removeAll();
}
@Override
public int getSize() {
return 0;
}
@Override
public ReadWriteLock getReadWriteLock() {
return readWriteLock;
}
}
在QRedisCache使用的辅助类JedisUtils及SerializeUtils实现如下：
public class JedisUtils {
private static final Logger logger = Logger.getLogger(JedisUtils.class);
private static JedisPool JEDISPOOL;
static {
Properties props = new Properties();
try {
props.load(JedisUtils.class.getResourceAsStream("/redis.properties"));
JedisPoolConfig conf = new JedisPoolConfig();
conf.setMaxIdle(Integer.valueOf(props.getProperty("jedis.pool.maxIdle")));
conf.setTestOnBorrow(Boolean.valueOf(props.getProperty("jedis.pool.testOnBorrow")));
conf.setTestOnReturn(Boolean.valueOf(props.getProperty("jedis.pool.testOnReturn")));
JEDISPOOL = new JedisPool(conf, props.getProperty("redis.ip"), Integer.valueOf(props.getProperty("redis.port")));
} catch (IOException e) {
logger.error("加载[jedis.properties]异常[" + e.getMessage() + "]", e);
}
}
public static Jedis getJedis() {
return JEDISPOOL.getResource();
}
public static void recycleJedis(Jedis jedis) {
jedis.close();
}
/**
* Redis存储Object序列化流
* */
public static void put(Object key, Object value) {
Jedis jedis = getJedis();
jedis.set(SerializeUtils.serialize(key), SerializeUtils.serialize(value));
recycleJedis(jedis);
}
public static <T> T get(Object key) {
Jedis jedis = getJedis();
T value = SerializeUtils.unserialize(jedis.get(SerializeUtils.serialize(key)));
recycleJedis(jedis);
return value;
}
public static Long remove(Object key) {
Jedis jedis = getJedis();
Long num = jedis.del(SerializeUtils.serialize(key));
recycleJedis(jedis);
return num;
}
public static void removeAll() {
Jedis jedis = getJedis();
jedis.flushDB();
recycleJedis(jedis);
}
}
public class SerializeUtils {
private static final Logger logger = Logger.getLogger(SerializeUtils.class);
private static void close(ObjectOutputStream objectOutputStream, ByteArrayOutputStream byteArrayOutputStream) {
try {
if (byteArrayOutputStream != null) {
byteArrayOutputStream.close();
}
if (objectOutputStream != null) {
objectOutputStream.close();
}
} catch (Exception e) {
e.printStackTrace();
logger.error("关闭IO资源异常[" + e.getMessage() + "]", e);
}
}
private static void close(ObjectInputStream objectInputStream, ByteArrayInputStream byteArrayInputStream) {
try {
if (objectInputStream != null) {
objectInputStream.close();
}
if (byteArrayInputStream != null) {
byteArrayInputStream.close();
}
} catch (Exception e) {
e.printStackTrace();
logger.error("关闭IO资源异常[" + e.getMessage() + "]", e);
}
}
public static byte[] serialize(Object object) {
ObjectOutputStream objectOutputStream = null;
ByteArrayOutputStream byteArrayOutputStream = null;
try {
byteArrayOutputStream = new ByteArrayOutputStream();
objectOutputStream = new ObjectOutputStream(byteArrayOutputStream);
objectOutputStream.writeObject(object);
byte[] bytes = byteArrayOutputStream.toByteArray();
return bytes;
} catch (Exception e) {
e.printStackTrace();
logger.error("序列化对象异常[" + e.getMessage() + "]", e);
} finally {
close(objectOutputStream, byteArrayOutputStream);
}
return null;
}
@SuppressWarnings("unchecked")
public static <T> T unserialize(byte[] bytes) {
if (bytes == null)
return null;
ByteArrayInputStream byteArrayInputStream = null;
ObjectInputStream objectInputStream = null;
try {
byteArrayInputStream = new ByteArrayInputStream(bytes);
objectInputStream = new ObjectInputStream(byteArrayInputStream);
return (T) objectInputStream.readObject();
} catch (Exception e) {
e.printStackTrace();
} finally {
close(objectInputStream, byteArrayInputStream);
}
return null;
}
}
Redis的配置文件redis.properties如下：
#redis服务器ip# redis.ip=192.168.2.107 #redis服务器端口号# redis.port=6379 #********jedis池参数设置********# #jedis的最大分配对象# jedis.pool.maxActive=3000 #jedis最大保存idel状态对象数 # jedis.pool.maxIdle=1000 #jedis池没有对象返回时，最大等待时间 # jedis.pool.maxWait=1500 #jedis调用borrowObject方法时，是否进行有效检查# jedis.pool.testOnBorrow=true #jedis调用returnObject方法时，是否进行有效检查 # jedis.pool.testOnReturn=true