Mybatis之运行原理

小土豆Yuki

发布于 2020-06-15 17:13:55

3180

发布于 2020-06-15 17:13:55

文章被收录于专栏：洁癖是一只狗洁癖是一只狗

mybatis运行流程是面试必备技能之一，下面我们就来开始我们的讲解

mybatisa层次图

mybatis执行流程

根据配置文件，初始化出Configuration
创建DefaultSqlSession对象(里面包含Configuration以及Exector)
DefaultSqlSession.getMapper(),获取Mapper接口对应的MapperProxy;
MapperProxy里面有(DefaultSqlSession)
执行增删改成
1. 调用DefaultSqlSession的增删改查(Exector)
2. 会创建一个StatementHandler对象(同时创建Parameterhandler和ResultSetHandler)
3. 调用StatementHandler预编译以及设置参数,使用ParamenterHandler给sql设置参数
4. 调用StateMentHandler的增删改查方法
5. ResultSetHandler封装结果

我们在详细看看每一步的具体步骤

1.根据配置文件创建SqlSessionFactory

Confuguration封装了多有配置文件的详细信息，把配置文件的信息解析并保存在Configuration对象中，返回包含了Confuguration的DefaultSqlSessionFactory对象，主要步骤如下

创建sqlsessionFactoryBuilder对象

public SqlSessionFactory build(InputStream inputStream, String environment, Properties properties) {
        SqlSessionFactory var5;
try {
            XMLConfigBuilder parser = new XMLConfigBuilder(inputStream, environment, properties);
            var5 = this.build(parser.parse());
        } catch (Exception var14) {
throw ExceptionFactory.wrapException("Error building SqlSession.", var14);
        } finally {
            ErrorContext.instance().reset();
try {
                inputStream.close();
            } catch (IOException var13) {
            }
        }
return var5;
    }

解析配置文件

public Configuration parse() {
if (this.parsed) {
throw new BuilderException("Each XMLConfigBuilder can only be used once.");
        } else {
this.parsed = true;
this.parseConfiguration(this.parser.evalNode("/configuration"));
return this.configuration;
        }
    }
private void parseConfiguration(XNode root) {
try {
            Properties settings = this.settingsAsPropertiess(root.evalNode("settings"));
this.propertiesElement(root.evalNode("properties"));
this.loadCustomVfs(settings);
this.typeAliasesElement(root.evalNode("typeAliases"));
this.pluginElement(root.evalNode("plugins"));
this.objectFactoryElement(root.evalNode("objectFactory"));
this.objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));
this.reflectorFactoryElement(root.evalNode("reflectorFactory"));
this.settingsElement(settings);
this.environmentsElement(root.evalNode("environments"));
this.databaseIdProviderElement(root.evalNode("databaseIdProvider"));
this.typeHandlerElement(root.evalNode("typeHandlers"));
this.mapperElement(root.evalNode("mappers"));
        } catch (Exception var3) {
throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + var3, var3);
        }
    }

返回sqlSessionFactoty,把上面解析的配置的Confuguration,放到构造sqlSessionFactory的build

public SqlSessionFactory build(Configuration config) {
return new DefaultSqlSessionFactory(config);
    }

2.返回sqlSession的实现类DefultSqlSession对象，它里面包含了Exextor和Configuration，Executor也会创建

主要如下重要步骤

构造sqlsession对象，包含Executor以及Configuration

private SqlSession openSessionFromDataSource(ExecutorType execType, TransactionIsolationLevel level, boolean autoCommit) {
        Transaction tx = null;
        DefaultSqlSession var8;
try {
            Environment environment = this.configuration.getEnvironment();
            TransactionFactory transactionFactory = this.getTransactionFactoryFromEnvironment(environment);
            tx = transactionFactory.newTransaction(environment.getDataSource(), level, autoCommit);
            Executor executor = this.configuration.newExecutor(tx, execType);
            var8 = new DefaultSqlSession(this.configuration, executor, autoCommit);
        } catch (Exception var12) {
this.closeTransaction(tx);
throw ExceptionFactory.wrapException("Error opening session.  Cause: " + var12, var12);
        } finally {
            ErrorContext.instance().reset();
        }

return var8;
    }

3.getMaper返回接口的代理对象,包含了sqlSession对象

根据type从MapperRegistry获取代理对象(MapperRegistry是在初始化Configuration绑定的信息),如下图中显示了MapperRegistry的信息。

public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
        MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
if (mapperProxyFactory == null) {
throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
        } else {
try {
return mapperProxyFactory.newInstance(sqlSession);
            } catch (Exception var5) {
throw new BindingException("Error getting mapper instance. Cause: " + var5, var5);
            }
        }
    }

4.查询流程

使用代理对象的invoke

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (Object.class.equals(method.getDeclaringClass())) {
try {
return method.invoke(this, args);
            } catch (Throwable var5) {
throw ExceptionUtil.unwrapThrowable(var5);
            }
        } else {
            MapperMethod mapperMethod = this.cachedMapperMethod(method);
return mapperMethod.execute(this.sqlSession, args);
        }
    }

在代理对象方法中使用MapperMethod.execute方法执行增删改查

public Object execute(SqlSession sqlSession, Object[] args) {
        Object param;
        Object result;
        switch(this.command.getType()) {
        case INSERT:
            param = this.method.convertArgsToSqlCommandParam(args);
            result = this.rowCountResult(sqlSession.insert(this.command.getName(), param));
break;
        case UPDATE:
            param = this.method.convertArgsToSqlCommandParam(args);
            result = this.rowCountResult(sqlSession.update(this.command.getName(), param));
break;
        case DELETE:
            param = this.method.convertArgsToSqlCommandParam(args);
            result = this.rowCountResult(sqlSession.delete(this.command.getName(), param));
break;
        case SELECT:
if (this.method.returnsVoid() && this.method.hasResultHandler()) {
this.executeWithResultHandler(sqlSession, args);
                result = null;
            } else if (this.method.returnsMany()) {
                result = this.executeForMany(sqlSession, args);
            } else if (this.method.returnsMap()) {
                result = this.executeForMap(sqlSession, args);
            } else if (this.method.returnsCursor()) {
                result = this.executeForCursor(sqlSession, args);
            } else {
                param = this.method.convertArgsToSqlCommandParam(args);
                result = sqlSession.selectOne(this.command.getName(), param);
            }
break;
        case FLUSH:
            result = sqlSession.flushStatements();
break;
default:
throw new BindingException("Unknown execution method for: " + this.command.getName());
        }
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;
        }
    }

最终也是调用DefalultSqlSession的selectList，且获取MappedStatement(包含每一个执行的方法对应的sql配置)

public <E> List<E> selectList(String statement, Object parameter, RowBounds rowBounds) {
        List var5;
try {
            MappedStatement ms = this.configuration.getMappedStatement(statement);
            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;
    }

使用BaseExecutor获取sql的相关信息(BoundSql)如下图

public <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
        BoundSql boundSql = ms.getBoundSql(parameter);
        CacheKey key = this.createCacheKey(ms, parameter, rowBounds, boundSql);
return this.query(ms, parameter, rowBounds, resultHandler, key, boundSql);
    }

在使用SimpleExecutor对象doquery(),重点是是四大对象的处理，statementHandler创建，以及使用ParameterHandler处理参数，以及查询结构使用resultHandler进行处理，最后返回结果。

public <E> List<E> doQuery(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
        Statement stmt = null;

        List var9;
try {
            Configuration configuration = ms.getConfiguration();
            StatementHandler handler = configuration.newStatementHandler(this.wrapper, ms, parameter, rowBounds, resultHandler, boundSql);
            stmt = this.prepareStatement(handler, ms.getStatementLog());
            var9 = handler.query(stmt, resultHandler);
        } finally {
this.closeStatement(stmt);
        }

return var9;
    }

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原始发表：2020-04-15，如有侵权请联系 cloudcommunity@tencent.com 删除

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