本文是作者原创,版权归作者所有.若要转载,请注明出处.本文以简单的select语句为例,只贴我觉得比较重要的源码,其他不重要非关键的就不贴了
主流程和insert语句差不多,这里主要讲不同的流程,前面配置解析就不看了
SqlSession sqlSession = sqlSessionFactory.openSession(); //通过动态代理实现接口 ,用动态代理对象去帮我们执行SQL //这里生成mapper实际类型是org.apache.ibatis.binding.MapperProxy DemoMapper mapper = sqlSession.getMapper(DemoMapper.class); //这里用生成的动态代理对象执行 String projId="0124569b738e405fb20b68bfef37f487"; String sectionName="标段"; List<ProjInfo> projInfos = mapper.selectAll(projId, sectionName); System.out.println(projInfos); //sqlSession.commit(); sqlSession.close();
点进去,看下方法sqlSession.getMapper(DemoMapper.class),这个调到下面这个方法
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { //这里就是动态代理生成的代理对象 final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } }
我们看下mapperProxyFactory.newInstance(sqlSession)这个方法
public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
继续点进去看
protected T newInstance(MapperProxy<T> mapperProxy) { return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); }
好,很明显了,这里用的jdk的动态代理,关于动态代理,这里就不赘述了,下次有机会在设计模式里专门讲一下.所以这里返回的是代理对象
继续往下看,我们看mapper.selectAll(projId, sectionName)这个方法debug进去,调的是jdk动态代理的invoke方法,里面就是具体的查询逻辑了
//这里method是接口DemoMapper的selectAll方法 @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { // 如果目标方法是Object类继承来的，直接调用目标方法 //method.getDeclaringClass()是接口DemoMapper的类对象,这里结果为false,跳过这一步 if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); //这里method是接口DemoMapper的selectAll方法,所以结果也为false,跳过这一步 } else if (method.isDefault()) { if (privateLookupInMethod == null) { return invokeDefaultMethodJava8(proxy, method, args); } else { return invokeDefaultMethodJava9(proxy, method, args); } } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } //这里将method放入缓存 // 从缓存中获取MapperMethod 对象,如果没有就创建新的并添加 final MapperMethod mapperMethod = cachedMapperMethod(method); //这是真正的执行方法 return mapperMethod.execute(sqlSession, args); }
缓存的东西,我们下次再说,我们继续点进去看
//就是这个执行方法 public Object execute(SqlSession sqlSession, Object[] args) { Object result; //command.getType()此时是select switch (command.getType()) { case INSERT: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.insert(command.getName(), param)); break; } case UPDATE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.update(command.getName(), param)); break; } case DELETE: { Object param = method.convertArgsToSqlCommandParam(args); result = rowCountResult(sqlSession.delete(command.getName(), param)); break; } //进入这个分支 case SELECT: //这里结果为false,不进这里 if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; //这里结果为真,进这里 } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); //这里结果为false,不进这里 } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); //这里结果为false,不进这里 } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else { // Object param = method.convertArgsToSqlCommandParam(args); //处理参数完成后后param是hashmap类型,key有两种,一种是#{}里面的参数名, // 另一种是(param1, param2, ...),value只有一种,就是我们的实际参数 //这里执行sql得到查询结果result,跟进去看下 result = sqlSession.selectOne(command.getName(), param); if (method.returnsOptional() && (result == null || !method.getReturnType().equals(result.getClass()))) { result = Optional.ofNullable(result); } } break; case FLUSH: result = sqlSession.flushStatements(); break; default: throw new BindingException("Unknown execution method for: " + command.getName()); } if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) { throw new BindingException("Mapper method '" + command.getName() + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ")."); } return result; }
继续往下看
private <E> Object executeForMany(SqlSession sqlSession, Object[] args) {
List<E> result;
Object param = method.convertArgsToSqlCommandParam(args);
if (method.hasRowBounds()) {
RowBounds rowBounds = method.extractRowBounds(args);
result = sqlSession.selectList(command.getName(), param, rowBounds);
} else {
//进这里,点进去看
result = sqlSession.selectList(command.getName(), param);
}
// issue #510 Collections & arrays support
if (!method.getReturnType().isAssignableFrom(result.getClass())) {
if (method.getReturnType().isArray()) {
return convertToArray(result);
} else {
return convertToDeclaredCollection(sqlSession.getConfiguration(), result);
}
}
return result;
}
继续
//这个是真正的sql执行方法了,statement是具体的方法名com.lusaisai.dao.DemoMapper.selectOne //parameter是参数名和真是的参数 @Override public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { //configuration对象根据statement,得到关于sql语句的相关信息 //这里得到的ms包含sql语句 MappedStatement ms = configuration.getMappedStatement(statement); //这里就是执行sql语句 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(); } }
继续跟
//执行语句这个方法,跟进去看下 @Override 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); //这个跟进去看戏,应该是真正的jdbc操作了 return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }
继续
@Override 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, boundSql); @SuppressWarnings("unchecked") List<E> list = (List<E>) tcm.getObject(cache, key); if (list == null) { list = delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); tcm.putObject(cache, key, list); // issue #578 and #116 } return list; } } //前面是缓存处理跟进去 return delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }
这里继续
@Override 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 { //进这里,继续跟 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; }
继续
private <E> List<E> queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { List<E> list; //key值就是待执行的sql localCache.putObject(key, EXECUTION_PLACEHOLDER); try { //跟进去 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; }
继续
@Override public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { Statement stmt = null; try { Configuration configuration = ms.getConfiguration(); StatementHandler handler = configuration.newStatementHandler(wrapper, ms, parameter, rowBounds, resultHandler, boundSql); stmt = prepareStatement(handler, ms.getStatementLog()); return handler.query(stmt, resultHandler); } finally { closeStatement(stmt); } }
跟一下return那行
@Override public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { //这里强转成预编译对象PreparedStatement PreparedStatement ps = (PreparedStatement) statement; ps.execute(); return resultSetHandler.handleResultSets(ps); }
好,我们看到PreparedStatement对象了,继续
public List<Object> handleResultSets(Statement stmt) throws SQLException { ErrorContext.instance().activity("handling results").object(mappedStatement.getId()); final List<Object> multipleResults = new ArrayList<>(); int resultSetCount = 0; ResultSetWrapper rsw = getFirstResultSet(stmt); List<ResultMap> resultMaps = mappedStatement.getResultMaps(); int resultMapCount = resultMaps.size(); validateResultMapsCount(rsw, resultMapCount); while (rsw != null && resultMapCount > resultSetCount) { ResultMap resultMap = resultMaps.get(resultSetCount); handleResultSet(rsw, resultMap, multipleResults, null); //这里已经执行完sql,生成结果集了 rsw = getNextResultSet(stmt); cleanUpAfterHandlingResultSet(); resultSetCount++; } String[] resultSets = mappedStatement.getResultSets(); if (resultSets != null) { while (rsw != null && resultSetCount < resultSets.length) { ResultMapping parentMapping = nextResultMaps.get(resultSets[resultSetCount]); if (parentMapping != null) { String nestedResultMapId = parentMapping.getNestedResultMapId(); ResultMap resultMap = configuration.getResultMap(nestedResultMapId); handleResultSet(rsw, resultMap, null, parentMapping); } rsw = getNextResultSet(stmt); cleanUpAfterHandlingResultSet(); resultSetCount++; } } return collapseSingleResultList(multipleResults); }
继续跟我注释的那行
private ResultSetWrapper getNextResultSet(Statement stmt) { // Making this method tolerant of bad JDBC drivers try { if (stmt.getConnection().getMetaData().supportsMultipleResultSets()) { // Crazy Standard JDBC way of determining if there are more results //这里的stmt已经包含可执行的sql了 if (!(!stmt.getMoreResults() && stmt.getUpdateCount() == -1)) { ResultSet rs = stmt.getResultSet(); if (rs == null) { return getNextResultSet(stmt); } else { return new ResultSetWrapper(rs, configuration); } } } } catch (Exception e) { // Intentionally ignored. } return null; }
最后再贴张网上找的图
好,到这里我们已经看完执行流程,其实封装了很多层,并没有全都要搞懂的必要,这里的重点是用了动态代理,底层肯定是jdbc操作,当然它还加了很多缓存和各种验证的代码.关于缓存的源码,有机会下次再看吧.
