深度解析MyBatis 动态 SQL 与缓存机制

@SelectProvider(type = UserSqlProvider.class, method = "selectByCondition")  
List<User> selectByCondition(Map<String, Object> params);  
// 自定义SQL提供器  
public class UserSqlProvider {  
    public String selectByCondition(Map<String, Object> params) {  
        SQL sql = new SQL();  
        sql.SELECT("*").FROM("users");  
        if (params.containsKey("username")) {  
            sql.WHERE("username = #{username}");  
        }  
        if (params.containsKey("age")) {  
            sql.WHERE("age >= #{age}");  
        }  
        return sql.toString();  
    }  
}  

String sql = new SQL()  
    .SELECT("id", "username")  
    .FROM("users")  
    .WHERE("status = 'ACTIVE'")  
    .ORDER_BY("create_time DESC")  
    .toString();  

public class DefaultSqlSession implements SqlSession {  
    private final Executor executor;  
    @Override  
    public <T> T selectOne(String statement, Object parameter) {  
        List<T> list = this.selectList(statement, parameter);  
        // 一级缓存逻辑在Executor中实现  
        return list.isEmpty() ? null : list.get(0);  
    }  
}  
public class BaseExecutor implements Executor {  
    private final PerpetualCache localCache;  
    @Override  
    public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {  
        BoundSql boundSql = ms.getBoundSql(parameter);  
        CacheKey key = createCacheKey(ms, parameter, rowBounds, boundSql);  
        return query(ms, parameter, rowBounds, resultHandler, key, boundSql);  
    }  
    @Override  
    public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {  
        // 先从一级缓存获取  
        List<E> list = (List<E>) localCache.getObject(key);  
        if (list != null) {  
            handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);  
            return list;  
        } else {  
            // 缓存未命中，执行数据库查询  
            list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);  
            return list;  
        }  
    }  
}  

<dependency>  
    <groupId>org.mybatis.caches</groupId>  
    <artifactId>mybatis-redis</artifactId>  
    <version>1.0.0-beta2</version>  
</dependency>  

<cache type="org.mybatis.caches.redis.RedisCache"/>  
<!-- redis.properties -->  
host=127.0.0.1  
port=6379  
timeout=2000  

<!-- 高并发场景优化配置 -->  
<cache  
    eviction="LRU"  
    flushInterval="300000" <!-- 5分钟刷新一次 -->  
    size="2048"          <!-- 增大缓存容量 -->  
    readOnly="true"/>    <!-- 只读模式提升性能 -->