MyBatis中一级缓存和二级缓存的区别

try (SqlSession session = sqlSessionFactory.openSession()) {
    BlogMapper mapper = session.getMapper(BlogMapper.class);
    
    // 第一次查询，数据来自数据库
    Blog blog1 = mapper.selectBlogById(1);
    // 第二次查询，相同的会话中，数据来自一级缓存
    Blog blog2 = mapper.selectBlogById(1);
}

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
    try {
        MappedStatement ms = configuration.getMappedStatement(statement);
        return executor.query(ms, wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER);
    } catch (Exception e) {
        throw ExceptionFactory.wrapException("Error querying database.  Cause: " + e, e);
    } finally {
        ErrorContext.instance().reset();
    }
}

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);
}

<!-- 在 mybatis-config.xml 中启用全局二级缓存 -->
<configuration>
    <settings>
        <setting name="cacheEnabled" value="true"/>
    </settings>
</configuration>

<!-- 在 Mapper.xml 中开启二级缓存 -->
<cache eviction="FIFO" flushInterval="60000" size="512" readOnly="true"/>

public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler,
                         CacheKey key, BoundSql boundSql) throws SQLException {
    Cache cache = ms.getCache();
    if (cache != null) {
        flushCacheIfRequired(ms);
        if (ms.isUseCache() && resultHandler == null) {
            ensureNoOutParams(ms, boundSql);
            @SuppressWarnings("unchecked")
            List<E> list = (List<E>) tcm.getObject(cache, key);
            if (list == null) {
                list = delegate.query(ms, parameter, rowBounds, resultHandler, key, boundSql);
                tcm.putObject(cache, key, list); // issue #578 and #116
            }
            return list;
        }
    }
    return delegate.query(ms, parameter, rowBounds, resultHandler, key, boundSql);
}