MyBatis深入理解和使用-MyBatis事务管理

傷城~ 2022-03-22 05:50 216阅读 0赞

## MyBatis深入理解和使用-MyBatis事务管理 ##

## 事务管理 ##

### JDBC事务 ###

public static boolean insert(Test test) throws SQLException {
            Connection connection = null;
            PreparedStatement preparedStatement = null;
            try {
                Class.forName("com.mysql.cj.jdbc.Driver");
                connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/testdb?useUnicode=true&characterEncoding=utf-8&useSSL=false&useJDBCCompliantTimezoneShift=true&useLegacyDatetimeCode=false&serverTimezone=UTC", "test", "123456");
                // 自动提交设置为false
                connection.setAutoCommit(false);
                preparedStatement = connection.prepareStatement("INSERT INTO test VALUES (?,?,?)");
                if (null != test.getId()) {
                    preparedStatement.setInt(1, test.getId());
                } else {
                    preparedStatement.setNull(1, INTEGER);
                }
                preparedStatement.setInt(2, test.getNums());
                preparedStatement.setString(3, test.getName());
                preparedStatement.execute();
                connection.commit();
                return true;
            } catch (ClassNotFoundException e) {
                e.printStackTrace();
            } catch (SQLException e) {
                e.printStackTrace();
            } finally {
                try {
                    if (null != connection) {
                        connection.close();
                    }
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            return true;
        }

### MyBatis自带事务 ###

SqlSession  -->  Executor  -->  Transaction  -->  Connection

之后就是JDBC的处理逻辑

### Mybatis-Spring-x.x.x.jar ###

**mapper是怎么注入进来的**

XML 或者 java Config- ->`MapperScannerConfigurer` -->  `BeanDefinitionRegistryPostProcessor` -->`BeanFactoryPostProcessor`告诉Spring去加载MyBatisConfig

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        if (this.processPropertyPlaceHolders) {
          processPropertyPlaceHolders();
        }
    
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
        scanner.setAddToConfig(this.addToConfig);
        scanner.setAnnotationClass(this.annotationClass);
        scanner.setMarkerInterface(this.markerInterface);
        scanner.setSqlSessionFactory(this.sqlSessionFactory);
        scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
        scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
        scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
        scanner.setResourceLoader(this.applicationContext);
        scanner.setBeanNameGenerator(this.nameGenerator);
        scanner.registerFilters();
        scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
      }

public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
        void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;
    }

Annotation --> `MapperScannerRegistrar` -->`ImportBeanDefinitionRegistrar` 告诉Spring去加载MyBatisConfig

public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
    
        AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    
        // this check is needed in Spring 3.1
        if (resourceLoader != null) {
          scanner.setResourceLoader(resourceLoader);
        }
    
        Class<? extends Annotation> annotationClass = annoAttrs.getClass("annotationClass");
        if (!Annotation.class.equals(annotationClass)) {
          scanner.setAnnotationClass(annotationClass);
        }
    
        Class<?> markerInterface = annoAttrs.getClass("markerInterface");
        if (!Class.class.equals(markerInterface)) {
          scanner.setMarkerInterface(markerInterface);
        }
    
        Class<? extends BeanNameGenerator> generatorClass = annoAttrs.getClass("nameGenerator");
        if (!BeanNameGenerator.class.equals(generatorClass)) {
          scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
        }
    
        Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
        if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
          scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
        }
    
        scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
        scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));
    
        List<String> basePackages = new ArrayList<String>();
        for (String pkg : annoAttrs.getStringArray("value")) {
          if (StringUtils.hasText(pkg)) {
            basePackages.add(pkg);
          }
        }
        for (String pkg : annoAttrs.getStringArray("basePackages")) {
          if (StringUtils.hasText(pkg)) {
            basePackages.add(pkg);
          }
        }
        for (Class<?> clazz : annoAttrs.getClassArray("basePackageClasses")) {
          basePackages.add(ClassUtils.getPackageName(clazz));
        }
        scanner.registerFilters();
        scanner.doScan(StringUtils.toStringArray(basePackages));
      }

public interface ImportBeanDefinitionRegistrar {
        void registerBeanDefinitions(AnnotationMetadata var1, BeanDefinitionRegistry var2);
    }

`sqlsession`的生命周期在没有`@Transaction`的情况下是request/method级别的；在有`@Transaction`的情况下

是`@Transaction`范围内的。

`Mapper`在没有spring的时候是`Method`级别的，在有的时候是全局的`Singleton`。

// set
    definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); 
    definition.setBeanClass(this.mapperFactoryBean.getClass());

// get
    Configuration configuration = getSqlSession().getConfiguration();

## 分页查询 ##

### 逻辑分页 ###

org.apache.ibatis.executor.resultset.DefaultResultSetHandler \# handleRowValuesForSimpleResultMap

private void handleRowValuesForSimpleResultMap(ResultSetWrapper rsw, ResultMap resultMap, ResultHandler<?> resultHandler, RowBounds rowBounds, ResultMapping parentMapping)
          throws SQLException {
        DefaultResultContext<Object> resultContext = new DefaultResultContext<Object>();
        // 判断要跳到响应的offset对应的位置
        skipRows(rsw.getResultSet(), rowBounds);
        while (shouldProcessMoreRows(resultContext, rowBounds) && rsw.getResultSet().next()) {
          ResultMap discriminatedResultMap = resolveDiscriminatedResultMap(rsw.getResultSet(), resultMap, null);
          Object rowValue = getRowValue(rsw, discriminatedResultMap);
          storeObject(resultHandler, resultContext, rowValue, parentMapping, rsw.getResultSet());
        }
      }
    
    // 具体判断逻辑
    private void skipRows(ResultSet rs, RowBounds rowBounds) throws SQLException {
        if (rs.getType() != ResultSet.TYPE_FORWARD_ONLY) {
          if (rowBounds.getOffset() != RowBounds.NO_ROW_OFFSET) {
            rs.absolute(rowBounds.getOffset());
          }
        } else {
            //具体实现
          for (int i = 0; i < rowBounds.getOffset(); i++) {
            rs.next();
          }
        }
      }

### 物理分页 ###

**拼SQL**

> select \* from table limit 1000, 10;

**插件**

> mybatis  PageHelper  https://github.com/pagehelper/Mybatis-PageHelper/tree/master/src/main/java/com/github/pagehelper
> 
> 自定义拦截器实现分页功能，拦截点如上述拦截器描述

*  mybatis 允许您在映射语句执行过程中的某些点拦截对调用。默认情况下, mybatis 允许插件拦截方法调用:

[MyBatis深入理解和使用-MyBatis缓存体系][MyBatis_-MyBatis]:[https://blog.csdn.net/shang\_xs/article/details/86656353][MyBatis_-MyBatis]

MyBatis深入理解和使用-TypeHandler:[https://blog.csdn.net/shang\_xs/article/details/86656173][https_blog.csdn.net_shang_xs_article_details_86656173]

[MyBatis_-MyBatis]: https://blog.csdn.net/shang_xs/article/details/86656353
[https_blog.csdn.net_shang_xs_article_details_86656173]: https://blog.csdn.net/shang_xs/article/details/86656173