<settings>
  <setting name="lazyLoadingEnabled" value="true"/>
  <setting name="aggressiveLazyLoading" value="false"/>
 </settings>

<resultMap id="blogAuthorResumtMap" type="Blog">
  <id column="id" property="id"/>
  <result column="title" property="title"/>
  <result column="category" property="category"/>
  <result column="author_id" property="author_id"/>
  <!--使用assocition支持延迟加载功能，配置延迟加载关联关系-->
  <association property="author" javaType="Author" select="selectAuthorById" column="author_id"/>
 </resultMap>

 <!--要使用延迟记载的方法-->
 <select id="selectBlogAuthor" resultMap="blogAuthorResumtMap">
  SELECT id,title,category,author_id FROM t_blog
 </select>

 <!--延迟加载查询博客对应的作者方法-->
 <select id="selectAuthorById" parameterType="int" resultType="Author">
  SELECT id,name from t_author where id=#{value}
 </select>

@Test
 public void getBlogAuthorByLazyloading(){
  SqlSession sqlSession=null;
  try{
   sqlSession=sqlSessionFactory.openSession();
   List<Blog> list = sqlSession.selectList("com.autohome.mapper.Author.selectBlogAuthor");
 
   for (Blog blog:list) {
    System.out.println("id:"+blog.getId()+",title:"+blog.getTitle()+",category:"+blog.getCategory());
    System.out.println("author:"+blog.getAuthor().getName());
   }
 
  }catch(Exception e){
   e.printStackTrace();
  }finally {
   sqlSession.close();
  }
 }

public void testCache(){
  SqlSession sqlSession=null;
  try{
   sqlSession=sqlSessionFactory.openSession();
 
   Author author = sqlSession.selectOne("com.autohome.mapper.Author.selectAuthorById",1);
   System.out.println("作者信息 id:"+author.getId()+",name:"+author.getName());
 
   author = sqlSession.selectOne("com.autohome.mapper.Author.selectAuthorById",1);
   System.out.println("作者信息2 id:"+author.getId()+",name:"+author.getName());
 
  }catch(Exception e){
   e.printStackTrace();
  }finally {
   sqlSession.close();
  }
 }

@Override
 public <T> T selectOne(String statement) {
 return this.<T>selectOne(statement, null);
 }
 
 @Override
 public <T> T selectOne(String statement, Object parameter) {
 // Popular vote was to return null on 0 results and throw exception on too many.
 List<T> list = this.<T>selectList(statement, parameter);
 if (list.size() == 1) {
  return list.get(0);
 } else if (list.size() > 1) {
  throw new TooManyResultsException("Expected one result (or null) to be returned by selectOne(), but found: " + list.size());
 } else {
  return null;
 }
 }

@Override
 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();
 }
 }

//先创建CacheKey
public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
 BoundSql boundSql = ms.getBoundSql(parameterObject);
 CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql);
 return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
 }
 
//再执行查询方法
public <E> List<E> query(MappedStatement ms, Object parameterObject, 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, parameterObject, boundSql);
  @SuppressWarnings("unchecked")
  List<E> list = (List<E>) tcm.getObject(cache, key);
  if (list == null) {
   list = delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
   tcm.putObject(cache, key, list); // issue #578 and #116
  }
  return list;
  }
 }
 return delegate.<E> query(ms, parameterObject, rowBounds, resultHandler, key, boundSql);
 }

public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
 ErrorContext.instance().resource(ms.getResource()).activity("executing a query").object(ms.getId());
 if (closed) {
 throw new ExecutorException("Executor was closed.");
 }
 if (queryStack == 0 && ms.isFlushCacheRequired()) {
 clearLocalCache();
 }
 List<E> list;
 try {
 queryStack++;
 list = resultHandler == null ? (List<E>) localCache.getObject(key) : null;
 if (list != null) {
  handleLocallyCachedOutputParameters(ms, key, parameter, boundSql);
 } else {
  list = queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql);
 }
 } finally {
 queryStack--;
 }
 if (queryStack == 0) {
 for (DeferredLoad deferredLoad : deferredLoads) {
  deferredLoad.load();
 }
 // issue #601
 deferredLoads.clear();
 if (configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) {
  // issue #482
  clearLocalCache();
 }
 }
 return list;
}

private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException {
 List<E> list;
 localCache.putObject(key, EXECUTION_PLACEHOLDER);
 try {
  list = doQuery(ms, parameter, rowBounds, resultHandler, boundSql);
 } finally {
  localCache.removeObject(key);
 }
 localCache.putObject(key, list);
 if (ms.getStatementType() == StatementType.CALLABLE) {
  localOutputParameterCache.putObject(key, parameter);
 }
 return list;
 }

@Test
 public void testCache2(){
  SqlSession sqlSession=null;
  SqlSession sqlSession2=null;
  try{
   sqlSession=sqlSessionFactory.openSession();
   sqlSession2=sqlSessionFactory.openSession();
 
   Author author = sqlSession.selectOne("com.autohome.mapper.Author.selectAuthorById",1);
   System.out.println("作者信息 id:"+author.getId()+",name:"+author.getName());
   sqlSession.close();
 
   Author author2 = sqlSession2.selectOne("com.autohome.mapper.Author.selectAuthorById",1);
   System.out.println("作者信息2 id:"+author2.getId()+",name:"+author2.getName());
   sqlSession2.close();
  }catch(Exception e){
   e.printStackTrace();
  }finally {
 
  }
 }

<select id="selectBlogAuthor" resultMap="blogAuthorResumtMap" useCache="false">
  SELECT id,title,category,author_id FROM t_blog
 </select>