當咱們在調用mybatis mapper的接口時發生了點什麼事呢 簡單的跟着源碼看了看sql
@Service("userService") public class UserServiceImpl implements IUserService { //UserMapper是個人接口,mybatis給它生成一個動態代理 @Resource private UserMapper userMapper; public User getUserById(int userId) { // TODO Auto-generated method stub //執行咱們接口所對應的sql return this.userMapper.selectByPrimaryKey(userId); } }
咱們查看一下調用堆棧數據庫
咱們直接到invoke中看一下發生了什麼事緩存
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { if (Object.class.equals(method.getDeclaringClass())) { return method.invoke(this, args); } else if (isDefaultMethod(method)) { return invokeDefaultMethod(proxy, method, args); } } catch (Throwable t) { throw ExceptionUtil.unwrapThrowable(t); } //查看是否有緩存 final MapperMethod mapperMethod = cachedMapperMethod(method); //繼續執行 return mapperMethod.execute(sqlSession, args); }
咱們接着進execute看一下代碼mybatis
public Object execute(SqlSession sqlSession, Object[] args) { Object result; 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; } case SELECT: if (method.returnsVoid() && method.hasResultHandler()) { executeWithResultHandler(sqlSession, args); result = null; } else if (method.returnsMany()) { result = executeForMany(sqlSession, args); } else if (method.returnsMap()) { result = executeForMap(sqlSession, args); } else if (method.returnsCursor()) { result = executeForCursor(sqlSession, args); } else {
//把輸入參數轉換一下 Object param = method.convertArgsToSqlCommandParam(args); //咱們查詢最後會走到這裏 result = sqlSession.selectOne(command.getName(), param); } 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; }
根據咱們需求不一樣 會case到不一樣的地方,咱們跟的是select 因此最後會走到sqlSession.selectOne部分,接着進入代碼app
public <T> T selectOne(String statement, Object parameter) { return this.sqlSessionProxy.<T> selectOne(statement, parameter); }
咱們能夠看出sqlSessionProxy也是一個代理對象,它代理的是誰呢,是咱們的DefaultSqlSession 咱們進入DefaultSqlSession查看ide
//咱們經過動態代理 會走到這裏 @Override public <T> T selectOne(String statement, Object parameter) { // Popular vote was to return null on 0 results and throw exception on too many. //而後會調用selectList 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; } }
進入selectList函數
@Override public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) { try { //這個是否是特別熟悉,咱們在加載xml的時候,會存儲到這個裏面 MappedStatement ms = configuration.getMappedStatement(statement); //執行sql 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(); } }
咱們會經過configuration.getMappedStatement(statement);把xml跟sql相關的 數據取出來,而後咱們進入executor.queryui
@Override public <E> List<E> query(MappedStatement ms, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException { //獲取sql BoundSql boundSql = ms.getBoundSql(parameterObject); //建立緩存 CacheKey key = createCacheKey(ms, parameterObject, rowBounds, boundSql); return query(ms, parameterObject, rowBounds, resultHandler, key, boundSql); }
boundSql 中存着的就是咱們真實的sql(下圖),createCacheKey我猜想是建立查詢緩存
而後咱們進入query函數this
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); }
咱們能夠看到,最初是查詢緩存,若是沒有的話 ,咱們又會進入一個queryspa
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 { //從這進入queryFromDatabase數據庫查詢 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; }
queryFromDatabase
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; }
咱們會先把緩存的key存起來,而後執行doQuery
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.<E>query(stmt, resultHandler); } finally { closeStatement(stmt); } }
獲取configuration 以後 執行handler.query
public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { return delegate.<E>query(statement, resultHandler); }
@Override public <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException { PreparedStatement ps = (PreparedStatement) statement; ps.execute(); return resultSetHandler.<E> handleResultSets(ps); }
執行到這裏 是否是看到jdbc的執行語句了,沒錯 就是PreparedStatement !
這篇簡單的說了一下mybatis的執行過程,若是有不對之處敬請指出,關於xml的加載還有動態代理的問題 請看我其餘文章