MyBatis高级技巧：性能优化实战
MyBatis 进阶：性能优化与高级特性
MyBatis 作为一款优秀的持久层框架，其核心功能是简化数据库操作。但在实际开发中，掌握其高级特性能够显著提升开发效率和系统性能。以下内容涵盖 MyBatis 的进阶使用技巧。
动态 SQL 的灵活运用
MyBatis 提供了强大的动态 SQL 功能，通过 <if>, <choose>, <foreach> 等标签实现条件查询。例如，构建一个多条件查询：
<select id="findUsers" resultType="User">
SELECT * FROM users
<where>
<if test="name != null">
AND name = #{name}
</if>
<if test="age != null">
AND age = #{age}
</if>
</where>
</select>
使用 <foreach> 标签处理批量插入操作：
<insert id="batchInsert">
INSERT INTO users (name, age) VALUES
<foreach item="user" collection="list" separator=",">
(#{user.name}, #{user.age})
</foreach>
</insert>
缓存机制深度解析
MyBatis 提供一级缓存和二级缓存机制。一级缓存默认开启，作用于 SqlSession 级别。二级缓存需要手动配置，作用于 Mapper 级别：
<cache eviction="LRU" flushInterval="60000" size="512" readOnly="true"/>
缓存的策略包括：
- LRU：最近最少使用
- FIFO：先进先出
- SOFT：软引用
- WEAK：弱引用
插件开发与拦截器
通过实现 Interceptor 接口可以自定义 MyBatis 插件，用于监控和修改 SQL 执行过程。例如实现一个性能监控插件：
@Intercepts({
@Signature(type= Executor.class, method="query",
args={MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})
})
public class PerformanceInterceptor implements Interceptor {
@Override
public Object intercept(Invocation invocation) throws Throwable {
long start = System.currentTimeMillis();
Object result = invocation.proceed();
long end = System.currentTimeMillis();
System.out.println("SQL执行耗时：" + (end - start) + "ms");
return result;
}
}
高级结果映射
复杂对象关系可以通过 <resultMap> 精细控制：
<resultMap id="detailedUser" type="User">
<id property="id" column="user_id"/>
<result property="name" column="user_name"/>
<collection property="roles" ofType="Role">
<id property="id" column="role_id"/>
<result property="name" column="role_name"/>
</collection>
</resultMap>
批量操作优化
使用 BatchExecutor 可以显著提升批量操作性能：
SqlSession session = sqlSessionFactory.openSession(ExecutorType.BATCH);
try {
UserMapper mapper = session.getMapper(UserMapper.class);
for (User user : users) {
mapper.insert(user);
}
session.commit();
} finally {
session.close();
}
类型处理器定制
自定义类型处理器处理特殊数据类型：
@MappedTypes(EncryptedString.class)
public class EncryptedStringTypeHandler extends BaseTypeHandler<EncryptedString> {
@Override
public void setNonNullParameter(PreparedStatement ps, int i,
EncryptedString parameter, JdbcType jdbcType) throws SQLException {
ps.setString(i, encrypt(parameter.getValue()));
}
@Override
public EncryptedString getNullableResult(ResultSet rs, String columnName)
throws SQLException {
String value = rs.getString(columnName);
return value == null ? null : new EncryptedString(decrypt(value));
}
}
多数据源支持
配置多个数据源并通过 @MapperScan 指定：
@Configuration
@MapperScan(basePackages = "com.dao.master", sqlSessionTemplateRef = "masterSqlSessionTemplate")
public class MasterDataSourceConfig {
@Bean
@ConfigurationProperties(prefix = "spring.datasource.master")
public DataSource masterDataSource() {
return DataSourceBuilder.create().build();
}
@Bean
public SqlSessionTemplate masterSqlSessionTemplate(
@Qualifier("masterDataSource") DataSource dataSource) throws Exception {
SqlSessionFactoryBean factory = new SqlSessionFactoryBean();
factory.setDataSource(dataSource);
return new SqlSessionTemplate(factory.getObject());
}
}
存储过程调用
通过 MyBatis 调用存储过程：
<select id="callProcedure" statementType="CALLABLE">
{call calculate_bonus(
#{employeeId, mode=IN},
#{year, mode=IN},
#{month, mode=IN},
#{bonus, mode=OUT, jdbcType=DECIMAL}
)}
</select>
分页插件集成
集成 PageHelper 实现物理分页：
PageHelper.startPage(1, 10);
List<User> users = userMapper.selectAll();
PageInfo<User> pageInfo = new PageInfo<>(users);
乐观锁实现
通过版本号控制实现乐观锁：
<update id="updateWithLock">
UPDATE products
SET name=#{name}, price=#{price}, version=version+1
WHERE id=#{id} AND version=#{version}
</update>
掌握这些进阶技术能够帮助开发者构建更高效、更健壮的持久层解决方案。实际应用中应根据具体场景选择合适的优化策略，平衡开发效率与系统性能。
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