1.Mybatis的架構
1.1 Mybatis的框架分層
1.2 MyBatis的實現原理
mybatis底層還是採用原生jdbc來對數據庫進行操作的，只是通過 SqlSessionFactory，SqlSession Executor,StatementHandler，ParameterHandler,ResultHandler和TypeHandler等幾個處理器封裝了這些過程
<code> 執行器：Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed) 參數處理器： ParameterHandler (getParameterObject, setParameters) 結構處理器 ResultSetHandler (handleResultSets, handleOutputParameters) sql查詢處理器：StatementHandler (prepare, parameterize, batch, update, query)/<code>
其中StatementHandler用通過ParameterHandler與ResultHandler分別進行參數預編譯 與結果處理。而ParameterHandler與ResultHandler都使用TypeHandler進行映射。如下圖：
2.Mybatis工作過程
通過讀mybatis的源碼進行分析mybatis的執行操作的整個過程，我們通過debug調試就可以知道Mybatis每一步做了什麼事，我先把debug每一步結果 截圖，然後在分析這個流程。
第一步:讀取配置文件，形成InputStream
2.1 創建SqlSessionFacotry的過程
從debug調試看出 返回的 sqlSessionFactory 是DefaultSesssionFactory類型的，但是configuration此時已經被初始化了。查看源碼後畫如下創建DefaultSessionFactory的時序圖：
2.2 創建SqlSession的過程
從debug調試 看出SqlSessinoFactory.openSession() 返回的sqlSession是 DefaultSession類型的，此SqlSession裡包含一個Configuration的對象，和一個Executor對象。查看源碼後畫如下創建DefaultSession的時序圖：
2.3 創建Mapper的過程
從debug調試可以看出，mapper是一個Mapper代理對象，而且初始化了Configuration對象，Executor的對象。查看源碼後畫如下創建Mapper的時序圖：
2.4 執行CRUD過程
2.4.1 以select為例查看各步執行的源碼
1.mapper.selectEmployeeList()其實是MapperProxy執行invoke方法，此方法顯示是判斷Method的方法是不是Object的toString等方法如果不是就執行MapperMethod
<code>public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {// 判斷Method的方法是不是Object的toString等方法 if(Object.class.equals(method.getDeclaringClass())) { try { return method.invoke(this, args); } catch (Throwable var5) { throw ExceptionUtil.unwrapThrowable(var5); } } else { //判斷private final Map<method> methodCache;這個map裡面有沒有這個方法的一級緩存，如果沒 MapperMethod mapperMethod = this.cachedMapperMethod(method); return mapperMethod.execute(this.sqlSession, args); } } //查詢一級緩存和設置一級緩存 private MapperMethod cachedMapperMethod(Method method) { MapperMethod mapperMethod = (MapperMethod)this.methodCache.get(method); if(mapperMethod == null) { mapperMethod = new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration()); this.methodCache.put(method, mapperMethod); } return mapperMethod; }/<method>/<code>
經過上面的調用後進入MapperMethod裡面執行
<code>//判斷sql命令類型public Object execute(SqlSession sqlSession, Object[] args) { Object param; Object result; if(SqlCommandType.INSERT == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.insert(this.command.getName(), param)); } else if(SqlCommandType.UPDATE == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.update(this.command.getName(), param)); } else if(SqlCommandType.DELETE == this.command.getType()) { param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.delete(this.command.getName(), param)); } else if(SqlCommandType.SELECT == this.command.getType()) { //我們測試的是select類型，則再判斷這個方法的返回類型 if(this.method.returnsVoid() && this.method.hasResultHandler()) { this.executeWithResultHandler(sqlSession, args); result = null; } else if(this.method.returnsMany()) { //我們是查詢列表，此方法執行 result = this.executeForMany(sqlSession, args); } else if(this.method.returnsMap()) { result = this.executeForMap(sqlSession, args); } else { param = this.method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(this.command.getName(), param); } } else { if(SqlCommandType.FLUSH != this.command.getType()) { throw new BindingException("Unknown execution method for: " + this.command.getName()); } result = sqlSession.flushStatements(); } if(result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) { throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ")."); } else { return result; } }private Object executeForMany(SqlSession sqlSession, Object[] args) {//將param做處理 自動處理為param1,param2.. Object param = this.method.convertArgsToSqlCommandParam(args); List result; if(this.method.hasRowBounds()) { RowBounds rowBounds = this.method.extractRowBounds(args); //調用該對象的DefaultSqlSession的selectList方法 result = sqlSession.selectList(this.command.getName(), param, rowBounds); } else { result = sqlSession.selectList(this.command.getName(), param); } return !this.method.getReturnType().isAssignableFrom(result.getClass())?(this.method.getReturnType().isArray()?this.convertToArray(result):this.convertToDeclaredCollection(sqlSession.getConfiguration(), result)):result; }//處理參數方法 public Object convertArgsToSqlCommandParam(Object[] args) { int paramCount = this.params.size(); if(args != null && paramCount != 0) { if(!this.hasNamedParameters && paramCount == 1) { return args[((Integer)this.params.keySet().iterator().next()).intValue()]; } else { Map<string> param = new MapperMethod.ParamMap(); int i = 0; for(Iterator i$ = this.params.entrySet().iterator(); i$.hasNext(); ++i) { Entry<integer> entry = (Entry)i$.next(); param.put(entry.getValue(), args[((Integer)entry.getKey()).intValue()]); String genericParamName = "param" + String.valueOf(i + 1); if(!param.containsKey(genericParamName)) { param.put(genericParamName, args[((Integer)entry.getKey()).intValue()]); } } return param; } } else { return null; } }/<integer>/<string>/<code>
調用DefaultSqlSession的selectList的方法
<code>public List selectList(String statement, Object parameter, RowBounds rowBounds) { List var5; try { //獲取MappedStatement對象 MappedStatement ms = this.configuration.getMappedStatement(statement); //調用cachingExecutor執行器的方法 var5 = this.executor.query(ms, this.wrapCollection(parameter), rowBounds, Executor.NO_RESULT_HANDLER); } catch (Exception var9) { throw ExceptionFactory.wrapException("Error querying database. Cause: " + var9, var9); } finally { ErrorContext.instance().reset(); } return var5; }//CachingExector的query方法public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { // BoundSql boundSql = ms.getBoundSql(parameterObject); CacheKey key = this.createCacheKey(ms, parameterObject, rowBounds, boundSql); //調用下2代碼 return this.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); } //2代碼 public List query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { Cache cache = ms.getCache(); if(cache != null) { this.flushCacheIfRequired(ms); if(ms.isUseCache() && resultHandler == null) { this.ensureNoOutParams(ms, parameterObject, boundSql); List list = (List)this.tcm.getObject(cache, key); if(list == null) { //這裡是調用Executor裡的query方法 如果開啟了緩存這掉CachingExecutor的 如果沒有則是調用BaseExecutor的 list = this.delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); this.tcm.putObject(cache, key, list); } return list; } } return this.delegate.query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }/<code>
BaseExecutor的query方法
<code>public List 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(this.closed) { throw new ExecutorException("Executor was closed."); } else { if(this.queryStack == 0 && ms.isFlushCacheRequired()) { this.clearLocalCache(); } List list; try { ++this.queryStack; list = resultHandler == null?(List)this.localCache.getObject(key):null; if(list != null) { this.handleLocallyCachedOutputParameters(ms, key, parameter, boundSql); } else { //如果緩存中沒有就從數據庫中查詢 list = this.queryFromDatabase(ms, parameter, rowBounds, resultHandler, key, boundSql); } } finally { --this.queryStack; } if(this.queryStack == 0) { Iterator i$ = this.deferredLoads.iterator(); while(i$.hasNext()) { BaseExecutor.DeferredLoad deferredLoad = (BaseExecutor.DeferredLoad)i$.next(); deferredLoad.load(); } this.deferredLoads.clear(); if(this.configuration.getLocalCacheScope() == LocalCacheScope.STATEMENT) { this.clearLocalCache(); } } return list; } }//從數據庫中查詢private List queryFromDatabase(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey key, BoundSql boundSql) throws SQLException { //放入緩存 this.localCache.putObject(key, ExecutionPlaceholder.EXECUTION_PLACEHOLDER); List list; try { //此處是調用子Executor的方法，ExecutorType默認是使用的SimpleExecutor list = this.doQuery(ms, parameter, rowBounds, resultHandler, boundSql); } finally { this.localCache.removeObject(key); } this.localCache.putObject(key, list); if(ms.getStatementType() == StatementType.CALLABLE) { this.localOutputParameterCache.putObject(key, parameter); } return list; }/<code>
SimpleExecutor的doQuery方法
<code>public List doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException { Statement stmt = null; List var9; try { Configuration configuration = ms.getConfiguration(); //創建StateMentHandler處理器 StatementHandler handler = configuration.newStatementHandler(this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql); //調用下3的方法 stmt = this.prepareStatement(handler, ms.getStatementLog()); //調用no4的方法 var9 = handler.query(stmt, resultHandler); } finally { this.closeStatement(stmt); } return var9; } //下3方法private Statement prepareStatement(StatementHandler handler, Log statementLog) throws SQLException { Connection connection = this.getConnection(statementLog); Statement stmt = handler.prepare(connection); //SatementHanlder 採用PreparedStatementHandler來實現此方法，而PreparedStatementHandler調用的是父接口ParameterHandler的方法 handler.parameterize(stmt); return stmt; }/<code>
ParameterHandler參數處理器的方法
<code>public interface ParameterHandler { Object getParameterObject(); //此方法是用DefaultParameterHandler實現的 void setParameters(PreparedStatement var1) throws SQLException;}/<code>
DefaultParameterHandler默認參數處理器的方法
<code>public void setParameters(PreparedStatement ps) { ErrorContext.instance().activity("setting parameters").object(this.mappedStatement.getParameterMap().getId()); List<parametermapping> parameterMappings = this.boundSql.getParameterMappings(); if(parameterMappings != null) { for(int i = 0; i < parameterMappings.size(); ++i) { ParameterMapping parameterMapping = (ParameterMapping)parameterMappings.get(i); if(parameterMapping.getMode() != ParameterMode.OUT) { String propertyName = parameterMapping.getProperty(); Object value; if(this.boundSql.hasAdditionalParameter(propertyName)) { value = this.boundSql.getAdditionalParameter(propertyName); } else if(this.parameterObject == null) { value = null; } else if(this.typeHandlerRegistry.hasTypeHandler(this.parameterObject.getClass())) { value = this.parameterObject; } else { MetaObject metaObject = this.configuration.newMetaObject(this.parameterObject); value = metaObject.getValue(propertyName); } //這裡用調用 TypeHandler類型映射處理器來映射 TypeHandler typeHandler = parameterMapping.getTypeHandler(); JdbcType jdbcType = parameterMapping.getJdbcType(); if(value == null && jdbcType == null) { jdbcType = this.configuration.getJdbcTypeForNull(); } try { //類型處理器設置參數映射 typeHandler.setParameter(ps, i + 1, value, jdbcType); } catch (TypeException var10) { throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + var10, var10); } catch (SQLException var11) { throw new TypeException("Could not set parameters for mapping: " + parameterMapping + ". Cause: " + var11, var11); } } } } }/<parametermapping>/<code>
no4的方法
<code> public List query(Statement statement, ResultHandler resultHandler) throws SQLException { //此處調用原生sql的處理器 PreparedStatement ps = (PreparedStatement)statement; //發出原生sql命令 ps.execute(); //採用ResultHandler結果處理器對結果集封裝 return this.resultSetHandler.handleResultSets(ps); }/<code>
ResultHandler代碼
<code>public interface ResultSetHandler { //此處調用的是DefaultResultSetHandler的方法 List handleResultSets(Statement var1) throws SQLException; void handleOutputParameters(CallableStatement var1) throws SQLException;}/<code>
DefaultResultSetHandler的方法
<code>public List<object> handleResultSets(Statement stmt) throws SQLException { ErrorContext.instance().activity("handling results").object(this.mappedStatement.getId()); List<object> multipleResults = new ArrayList(); int resultSetCount = 0; ResultSetWrapper rsw = this.getFirstResultSet(stmt); List<resultmap> resultMaps = this.mappedStatement.getResultMaps(); int resultMapCount = resultMaps.size(); this.validateResultMapsCount(rsw, resultMapCount); while(rsw != null && resultMapCount > resultSetCount) { ResultMap resultMap = (ResultMap)resultMaps.get(resultSetCount); this.handleResultSet(rsw, resultMap, multipleResults, (ResultMapping)null); rsw = this.getNextResultSet(stmt); this.cleanUpAfterHandlingResultSet(); ++resultSetCount; } String[] resultSets = this.mappedStatement.getResulSets(); if(resultSets != null) { while(rsw != null && resultSetCount < resultSets.length) { ResultMapping parentMapping = (ResultMapping)this.nextResultMaps.get(resultSets[resultSetCount]); if(parentMapping != null) { String nestedResultMapId = parentMapping.getNestedResultMapId(); ResultMap resultMap = this.configuration.getResultMap(nestedResultMapId); this.handleResultSet(rsw, resultMap, (List)null, parentMapping); } rsw = this.getNextResultSet(stmt); this.cleanUpAfterHandlingResultSet(); ++resultSetCount; } } return this.collapseSingleResultList(multipleResults); }//處理結果集 private void handleResultSet(ResultSetWrapper rsw, ResultMap resultMap, List<object> multipleResults, ResultMapping parentMapping) throws SQLException { try { if(parentMapping != null) { this.handleRowValues(rsw, resultMap, (ResultHandler)null, RowBounds.DEFAULT, parentMapping); } else if(this.resultHandler == null) { DefaultResultHandler defaultResultHandler = new DefaultResultHandler(this.objectFactory); this.handleRowValues(rsw, resultMap, defaultResultHandler, this.rowBounds, (ResultMapping)null); multipleResults.add(defaultResultHandler.getResultList()); } else { this.handleRowValues(rsw, resultMap, this.resultHandler, this.rowBounds, (ResultMapping)null); } } finally { this.closeResultSet(rsw.getResultSet()); } }private void handleRowValues(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException { if(resultMap.hasNestedResultMaps()) { this.ensureNoRowBounds(); this.checkResultHandler(); this.handleRowValuesForNestedResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping); } else { this.handleRowValuesForSimpleResultMap(rsw, resultMap, resultHandler, rowBounds, parentMapping); } } private void handleRowValuesForNestedResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler> resultHandler, RowBounds rowBounds, ResultMapping parentMapping) throws SQLException { DefaultResultContext<object> resultContext = new DefaultResultContext(); this.skipRows(rsw.getResultSet(), rowBounds); Object rowValue = null; while(this.shouldProcessMoreRows(resultContext, rowBounds) && rsw.getResultSet().next()) { ResultMap discriminatedResultMap = this.resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, (String)null); CacheKey rowKey = this.createRowKey(discriminatedResultMap, rsw, (String)null); Object partialObject = this.nestedResultObjects.get(rowKey); if(this.mappedStatement.isResultOrdered()) { if(partialObject == null && rowValue != null) { this.nestedResultObjects.clear(); this.storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet()); } //獲取行的值 rowValue = this.getRowValue(rsw, discriminatedResultMap, rowKey, (String)null, partialObject); } else { rowValue = this.getRowValue(rsw, discriminatedResultMap, rowKey, (String)null, partialObject); if(partialObject == null) { this.storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet()); } } } if(rowValue != null && this.mappedStatement.isResultOrdered() && this.shouldProcessMoreRows(resultContext, rowBounds)) { this.storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet()); } } String resultMapId = resultMap.getId(); Object resultObject = partialObject; if(partialObject != null) { MetaObject metaObject = this.configuration.newMetaObject(partialObject); this.putAncestor(partialObject, resultMapId, columnPrefix); this.applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, false); this.ancestorObjects.remove(resultMapId); } else { ResultLoaderMap lazyLoader = new ResultLoaderMap(); resultObject = this.createResultObject(rsw, resultMap, lazyLoader, columnPrefix); if(resultObject != null && !this.typeHandlerRegistry.hasTypeHandler(resultMap.getType())) { MetaObject metaObject = this.configuration.newMetaObject(resultObject); boolean foundValues = !resultMap.getConstructorResultMappings().isEmpty(); if(this.shouldApplyAutomaticMappings(resultMap, true)) { foundValues = this.applyAutomaticMappings(rsw, resultMap, metaObject, columnPrefix) || foundValues; } foundValues = this.applyPropertyMappings(rsw, resultMap, metaObject, lazyLoader, columnPrefix) || foundValues; this.putAncestor(resultObject, resultMapId, columnPrefix); foundValues = this.applyNestedResultMappings(rsw, resultMap, metaObject, columnPrefix, combinedKey, true) || foundValues; this.ancestorObjects.remove(resultMapId); foundValues = lazyLoader.size() > 0 || foundValues; resultObject = foundValues?resultObject:null; } if(combinedKey != CacheKey.NULL_CACHE_KEY) { this.nestedResultObjects.put(combinedKey, resultObject); } } return resultObject; }private boolean shouldApplyAutomaticMappings(ResultMap resultMap, boolean isNested) { return resultMap.getAutoMapping() != null?resultMap.getAutoMapping().booleanValue():(isNested?AutoMappingBehavior.FULL == this.configuration.getAutoMappingBehavior():AutoMappingBehavior.NONE != this.configuration.getAutoMappingBehavior()); } private boolean applyAutomaticMappings(ResultSetWrapper rsw, ResultMap resultMap, MetaObject metaObject, String columnPrefix) throws SQLException { List<defaultresultsethandler.unmappedcolumautomapping> autoMapping = this.createAutomaticMappings(rsw, resultMap, metaObject, columnPrefix); boolean foundValues = false; if(autoMapping.size() > 0) { Iterator i$ = autoMapping.iterator(); while(true) { //這裡使用了內部類對參數和結果集進行映射 DefaultResultSetHandler.UnMappedColumAutoMapping mapping; Object value; do { if(!i$.hasNext()) { return foundValues; } mapping = (DefaultResultSetHandler.UnMappedColumAutoMapping)i$.next(); value = mapping.typeHandler.getResult(rsw.getResultSet(), mapping.column); } while(value == null && !this.configuration.isCallSettersOnNulls()); if(value != null || !mapping.primitive) { metaObject.setValue(mapping.property, value); } foundValues = true; } } else { return foundValues; } } private static class UnMappedColumAutoMapping { private final String column; private final String property; private final TypeHandler> typeHandler; private final boolean primitive; //此處才類型器對結果進行映射 public UnMappedColumAutoMapping(String column, String property, TypeHandler> typeHandler, boolean primitive) { this.column = column; this.property = property; this.typeHandler = typeHandler; this.primitive = primitive; } }/<defaultresultsethandler.unmappedcolumautomapping>/<object>/<object>/<resultmap>/<object>/<object>/<code>
JAVA進階架構程序員福利：我這裡還總結整理了比較全面的JAVA相關的面試資料，都已經整理成了
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