前言
最近看了一个讲如何面试的视频，里面说到不要只写自己阅读过某某源码，要把它体现在项目中，就算自己做的项目中没有，也可以说自己看到别人的项目中利用了某个框架的某些特性，于是我就准备自己动手试试，学习一下优秀框架的精髓，我手动整合了spring和mybatis，视图体会mybatis的优秀之处。
开始
要开始整合spring和mybatis，自然是要先搭建一个maven的项目，我在整合spring和mybatis的同时还整合了log4j方便查看日志，整合了阿里的druid作为mysql的数据库连接池，由于我只是要整合spring和mybatis并找到mybatis基于spring的扩展点及整合的原理，没有必要使用web项目，所以我只引入了spring-context包。项目pom文件如下
-
<?xml version="1.0" encoding="UTF-8"?>
-
<project xmlns="http://maven.apache.org/POM/4.0.0"
-
xmlns:xsi=
"http://www.w3.org/2001/XMLSchema-instance"
-
xsi:schemaLocation=
"http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-
<modelVersion>4.0.0
</modelVersion>
-
-
<groupId>com.ww
</groupId>
-
<artifactId>mybatis-spring
</artifactId>
-
<version>1.0-SNAPSHOT
</version>
-
<dependencies>
-
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis -->
-
<dependency>
-
<groupId>org.mybatis
</groupId>
-
<artifactId>mybatis
</artifactId>
-
<version>3.4.6
</version>
-
</dependency>
-
<!-- https://mvnrepository.com/artifact/org.springframework/spring-context -->
-
<dependency>
-
<groupId>org.springframework
</groupId>
-
<artifactId>spring-context
</artifactId>
-
<version>4.3.25.RELEASE
</version>
-
</dependency>
-
-
<!-- https://mvnrepository.com/artifact/mysql/mysql-connector-java -->
-
<dependency>
-
<groupId>mysql
</groupId>
-
<artifactId>mysql-connector-java
</artifactId>
-
<version>5.1.47
</version>
-
</dependency>
-
-
<!-- https://mvnrepository.com/artifact/org.springframework/spring-jdbc -->
-
<dependency>
-
<groupId>org.springframework
</groupId>
-
<artifactId>spring-jdbc
</artifactId>
-
<version>4.3.25.RELEASE
</version>
-
</dependency>
-
<!-- https://mvnrepository.com/artifact/org.apache.logging.log4j/log4j-core -->
-
<dependency>
-
<groupId>log4j
</groupId>
-
<artifactId>log4j
</artifactId>
-
<version>1.2.17
</version>
-
</dependency>
-
-
-
<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis-spring -->
-
<dependency>
-
<groupId>org.mybatis
</groupId>
-
<artifactId>mybatis-spring
</artifactId>
-
<version>1.3.2
</version>
-
</dependency>
-
-
<dependency>
-
<groupId>org.projectlombok
</groupId>
-
<artifactId>lombok
</artifactId>
-
<version>1.18.10
</version>
-
<scope>compile
</scope>
-
</dependency>
-
<!-- https://mvnrepository.com/artifact/com.alibaba/druid -->
-
<dependency>
-
<groupId>com.alibaba
</groupId>
-
<artifactId>druid
</artifactId>
-
<version>1.1.10
</version>
-
</dependency>
-
-
</dependencies>
-
-
</project>
由于我不喜欢使用xml，所以本次搭建我是用了纯注解的形式，在项目的resource目录下，我建立了application.properties文件
-
spring.datasource.username=root
-
spring.datasource.password=
123456
-
spring.datasource.url=jdbc:mysql:
//localhost:3306/testmybatis
-
spring.datasource.driver=com.mysql.jdbc.Driver
编写配置类，获取application.properties中配置的数据库信息
-
@Configuration
-
@PropertySource(
"classpath:application.properties")
-
public
class PropertiesConfig {
-
@Value(
"${spring.datasource.url}")
-
public String url;
-
@Value(
"${spring.datasource.username}")
-
public String username;
-
@Value(
"${spring.datasource.password}")
-
public String password;
-
@Value(
"${spring.datasource.driver}")
-
public String driver;
-
-
-
public String getUrl() {
-
return url;
-
}
-
-
public String getUsername() {
-
return username;
-
}
-
-
public String getPassword() {
-
return password;
-
}
-
-
public String getDriver() {
-
return driver;
-
}
-
}
mapper文件如下
-
public
interface UserMapper {
-
@Select(
"select id,name,height,weight from user where id=#{id}")
-
public User selectUser(Integer id);
-
}
实体类
-
@Data
-
public
class User {
-
private
int id;
-
private String name;
-
private String height;
-
private String weight;
-
}
相对应的，在mysql中我建了一个数据库，表名为user
service类
-
@Service
-
public
class UserService{
-
-
@Autowired
-
UserMapper mapper;
-
public User getUser(int id) {
-
//一开始log4j并没有输出日志，在官网上查了之后说加上这句话就可以打印日志了
-
org.apache.ibatis.logging.LogFactory.useLog4JLogging();
-
return mapper.selectUser(id);
-
}
-
}
让spring来启动的主配置类
-
@Configuration
-
@ComponentScan(
"com.ww")
-
@MapperScan(
"com.ww.mapper")
-
@PropertySource(
"classpath:application.properties")
-
public
class MybatisConfig {
-
//这些都是mybatis-spring官网上的例子，照着改改就行
-
@Bean
-
public DataSource dataSource(PropertiesConfig config) {
-
DruidDataSource dataSource =
new DruidDataSource();
-
dataSource.setDriverClassName(config.getDriver());
-
dataSource.setUrl(config.getUrl());
-
dataSource.setPassword(config.getPassword());
-
dataSource.setUsername(config.getUsername());
-
return dataSource;
-
}
-
//这些都是mybatis-spring官网上的例子，照着改改就行
-
@Bean
-
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
-
SqlSessionFactoryBean factoryBean =
new SqlSessionFactoryBean();
-
factoryBean.setDataSource(dataSource);
-
return factoryBean.getObject();
-
}
-
}
到这里项目算搭建完成了，接下来我们运行项目，来观察mybatis整合spring之后的运行过程，以及mybatis整合spring和不整合spring究竟有什么不同
首先我们看到主配置类上有一行@MapperScan的注解，表示扫描mapper到spring容器中，把mapper交给spring管理，那么我想知道mapper是什么时候被spring扫描并注入的呢，我们点进这个注解，看到这个注解是一个组合注解，其中有这么一行注解引起了我的注意
@Import(MapperScannerRegistrar.class)这个注解是什么意思呢，Import注解的意思是导入资源，那么我们看看它导入的是个什么资源，看类的名字，我猜想这可能是一个mapper扫描器的注册器，于是我就点进去看看
-
public
class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
-
-
private ResourceLoader resourceLoader;
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
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();
-
//调用ClassPathMapperScanner中的doScan方法，来扫描mapper并组装成beanDefinition
-
scanner.doScan(StringUtils.toStringArray(basePackages));
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
public void setResourceLoader(ResourceLoader resourceLoader) {
-
this.resourceLoader = resourceLoader;
-
}
-
-
}
可以看到这个类实现了ImportBeanDefinitionRegistrar这个接口，这就引出了spring的第一个扩展点，ImportBeanDefinitionRegistrar接口可以用来动态注册bean，它可以支持我们自己写的代码封装成BeanDefinition对象。在这里，mybatis作为一个第三方框架因为没有办法像第一方组件那样使用@Component或者@Service来表示这是一个需要注入的bean，所以只能扩展这个接口来动态的注入bean。
我们再来看registerBeanDefinitions这个方法，这个方法的含义就是注册bd(为了方便起见，以下beanDefinition都简称bd），我们看到方法最后调用了ClassPathMapperScanner的doScan()方法，我们看看ClassPathMapperScanner这个类
-
public
class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {
-
...
-
}
这个类属于spring-mybatis包下，继承了spring的ClassPathBeanDefinitionScanner类
-
@Override
-
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
-
//调用spring的doScan方法来扫描bd
-
Set<BeanDefinitionHolder> beanDefinitions =
super.doScan(basePackages);
-
-
if (beanDefinitions.isEmpty()) {
-
logger.warn(
"No MyBatis mapper was found in '" + Arrays.toString(basePackages) +
"' package. Please check your configuration.");
-
}
else {
-
//扫描完成后执行bd处理
-
processBeanDefinitions(beanDefinitions);
-
}
-
-
return beanDefinitions;
-
}
由于spring先执行componentScan，我把断点打在ClassPathBeanDefinitionScanner的doScan方法中的时候，首先扫描我自己的bean的时候也会进入这个断点，本次由于不分析componentScan，这一部分略过。跳过这个断点，此时控制台上输出
-
Registering bean definition
for
@Bean method com.ww.config.MybatisConfig.dataSource()
-
Registering bean definition
for
@Bean method com.ww.config.MybatisConfig.sqlSessionFactory()
表示我自己的bean已经注册完成了，接下来就应该进入mapper扫描了，我把断点打在MapperScannerRegistrar类中registerBeanDefinitions()方法的第一行，果然断点跳了进来，一路执行下去，当执行完ClassPathBeanDefinitionScanner的doScan的方法之后，控制台输出一句：
Identified candidate component class: file [E:\mycode\gitclone\mybatis-spring\target\classes\com\ww\mapper\UserMapper.class]确认了候选的组件类，也就是说明spring已经扫描到mapper了，同时spring已经注册了bd，接下来再执行，则会进入processBeanDefinitions()方法
-
//处理注册好的bd
-
private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
-
GenericBeanDefinition definition;
-
for (BeanDefinitionHolder holder : beanDefinitions) {
-
definition = (GenericBeanDefinition) holder.getBeanDefinition();
-
-
if (logger.isDebugEnabled()) {
-
logger.debug(
"Creating MapperFactoryBean with name '" + holder.getBeanName()
-
+
"' and '" + definition.getBeanClassName() +
"' mapperInterface");
-
}
-
-
// the mapper interface is the original class of the bean
-
// but, the actual class of the bean is MapperFactoryBean
-
definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName());
// issue #59
-
//bd中加入mapperFactoryBean类，由此可见一个mapper对应的beanClass就是mapperFactoryBean,这是mybatis核心类之一，会详细说
-
definition.setBeanClass(
this.mapperFactoryBean.getClass());
-
-
definition.getPropertyValues().add(
"addToConfig",
this.addToConfig);
-
-
boolean explicitFactoryUsed =
false;
-
if (StringUtils.hasText(
this.sqlSessionFactoryBeanName)) {
-
definition.getPropertyValues().add(
"sqlSessionFactory",
new RuntimeBeanReference(
this.sqlSessionFactoryBeanName));
-
explicitFactoryUsed =
true;
-
}
else
if (
this.sqlSessionFactory !=
null) {
-
definition.getPropertyValues().add(
"sqlSessionFactory",
this.sqlSessionFactory);
-
explicitFactoryUsed =
true;
-
}
-
-
if (StringUtils.hasText(
this.sqlSessionTemplateBeanName)) {
-
if (explicitFactoryUsed) {
-
logger.warn(
"Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
-
}
-
definition.getPropertyValues().add(
"sqlSessionTemplate",
new RuntimeBeanReference(
this.sqlSessionTemplateBeanName));
-
explicitFactoryUsed =
true;
-
}
else
if (
this.sqlSessionTemplate !=
null) {
-
if (explicitFactoryUsed) {
-
logger.warn(
"Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
-
}
-
definition.getPropertyValues().add(
"sqlSessionTemplate",
this.sqlSessionTemplate);
-
explicitFactoryUsed =
true;
-
}
-
-
if (!explicitFactoryUsed) {
-
if (logger.isDebugEnabled()) {
-
logger.debug(
"Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() +
"'.");
-
}
-
//自动注入类型为byType
-
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
-
}
-
}
-
}
等这个方法处理完成之后，整个bd算是建立完了，接下来mybatis就开始初始化的过程了，首先我们来看之前被添加进bd中的MapperFactoryBean类
-
public
class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {
-
-
private Class<T> mapperInterface;
-
-
private
boolean addToConfig =
true;
-
-
public MapperFactoryBean() {
-
//intentionally empty
-
}
-
-
public MapperFactoryBean(Class<T> mapperInterface) {
-
this.mapperInterface = mapperInterface;
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
protected void checkDaoConfig() {
-
super.checkDaoConfig();
-
-
notNull(
this.mapperInterface,
"Property 'mapperInterface' is required");
-
-
Configuration configuration = getSqlSession().getConfiguration();
-
if (
this.addToConfig && !configuration.hasMapper(
this.mapperInterface)) {
-
try {
-
configuration.addMapper(
this.mapperInterface);
-
}
catch (Exception e) {
-
logger.error(
"Error while adding the mapper '" +
this.mapperInterface +
"' to configuration.", e);
-
throw
new IllegalArgumentException(e);
-
}
finally {
-
ErrorContext.instance().reset();
-
}
-
}
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
public T getObject() throws Exception {
-
return getSqlSession().getMapper(
this.mapperInterface);
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
public Class<T> getObjectType() {
-
return
this.mapperInterface;
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
public boolean isSingleton() {
-
return
true;
-
}
-
-
//------------- mutators --------------
-
-
/**
-
* Sets the mapper interface of the MyBatis mapper
-
*
-
* @param mapperInterface class of the interface
-
*/
-
public void setMapperInterface(Class<T> mapperInterface) {
-
this.mapperInterface = mapperInterface;
-
}
-
-
/**
-
* Return the mapper interface of the MyBatis mapper
-
*
-
* @return class of the interface
-
*/
-
public Class<T> getMapperInterface() {
-
return mapperInterface;
-
}
-
-
/**
-
* If addToConfig is false the mapper will not be added to MyBatis. This means
-
* it must have been included in mybatis-config.xml.
-
* <p/>
-
* If it is true, the mapper will be added to MyBatis in the case it is not already
-
* registered.
-
* <p/>
-
* By default addToCofig is true.
-
*
-
* @param addToConfig
-
*/
-
public void setAddToConfig(boolean addToConfig) {
-
this.addToConfig = addToConfig;
-
}
-
-
/**
-
* Return the flag for addition into MyBatis config.
-
*
-
* @return true if the mapper will be added to MyBatis in the case it is not already
-
* registered.
-
*/
-
public boolean isAddToConfig() {
-
return addToConfig;
-
}
-
}
MapperFactoryBean扩展了Spring的FactoryBean接口，FactoryBean作为Spring的扩展点，FactoryBean的功能是可以让我们自定义Bean的创建过程
-
//返回的对象实例
-
T getObject() throws Exception;
-
//Bean的类型
-
Class<?> getObjectType();
-
//true是单例，false是非单例 在Spring5.0中此方法利用了JDK1.8的新特性变成了default方法，返回true
-
boolean isSingleton();
同时MapperFactory还继承了SqlSessionDaoSupport类，SqlSessionDaoSupport类又继承了Spring的DaoSupport类，利用了Spring中InitializingBean这个扩展点，在属性设置之后对bean进行操作，我们来看SqlSessionDaoSupport类和DaoSupport类都是做什么的
-
public
abstract
class SqlSessionDaoSupport extends DaoSupport {
-
-
private SqlSession sqlSession;
-
-
private
boolean externalSqlSession;
-
-
//设置sqlSessionFactory,由于mapperScan最后执行了definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE)，所以这个set方法会自动注入进spring容器中
-
public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
-
if (!
this.externalSqlSession) {
-
this.sqlSession =
new SqlSessionTemplate(sqlSessionFactory);
-
}
-
}
-
//设置sqlSessionTemplate，spring-mybatis的核心类之一，替代了普通mybatis中的DefaultSqlSession类，这个类控制sqlSession，包含一个内部类用来执行动态代理,同时sqlSessionTemplate类线程安全，可以在spring中作为单例bean使用
-
public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
-
this.sqlSession = sqlSessionTemplate;
-
this.externalSqlSession =
true;
-
}
-
-
/**
-
* Users should use this method to get a SqlSession to call its statement methods
-
* This is SqlSession is managed by spring. Users should not commit/rollback/close it
-
* because it will be automatically done.
-
*
-
* @return Spring managed thread safe SqlSession
-
*/
-
public SqlSession getSqlSession() {
-
return
this.sqlSession;
-
}
-
-
/**
-
* {@inheritDoc}
-
*/
-
@Override
-
protected void checkDaoConfig() {
-
notNull(
this.sqlSession,
"Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
-
}
-
-
}
-
-
//实现InitializingBean接口，会执行afterPropertiesSet()方法，在mybatis整合了spring后会执行MapperFactoryBean类中的checkDaoConfig()方法
-
public
abstract
class DaoSupport implements InitializingBean {
-
-
/** Logger available to subclasses */
-
protected
final Log logger = LogFactory.getLog(getClass());
-
-
-
@Override
-
public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
-
// Let abstract subclasses check their configuration.
-
checkDaoConfig();
-
-
// Let concrete implementations initialize themselves.
-
try {
-
initDao();
-
}
-
catch (Exception ex) {
-
throw
new BeanInitializationException(
"Initialization of DAO failed", ex);
-
}
-
}
-
-
/**
-
* Abstract subclasses must override this to check their configuration.
-
* <p>Implementors should be marked as {@code final} if concrete subclasses
-
* are not supposed to override this template method themselves.
-
* @throws IllegalArgumentException in case of illegal configuration
-
*/
-
protected abstract void checkDaoConfig() throws IllegalArgumentException;
-
-
/**
-
* Concrete subclasses can override this for custom initialization behavior.
-
* Gets called after population of this instance's bean properties.
-
* @throws Exception if DAO initialization fails
-
* (will be rethrown as a BeanInitializationException)
-
* @see org.springframework.beans.factory.BeanInitializationException
-
*/
-
protected void initDao() throws Exception {
-
}
-
-
}
把断点打在MapperFactoryBean类中的checkDaoConfig()方法上，继续执行，我们看到执行了configuration.addMapper(this.mapperInterface)，点进去，我们看到跳入了org.apache.ibatis.session.Configuration类中的addMapper方法
-
//mapper注册器，添加和获取mapper的实际类
-
protected
final MapperRegistry mapperRegistry =
new MapperRegistry(
this);
-
public <T>
void addMapper(Class<T> type) {
-
mapperRegistry.addMapper(type);
-
}
于是乎再进入一层
-
//mapper被加入到MapperProxyFactory类中
-
private
final Map<Class<?>, MapperProxyFactory<?>> knownMappers =
new HashMap<Class<?>, MapperProxyFactory<?>>();
-
public <T>
void addMapper(Class<T> type) {
-
if (type.isInterface()) {
-
if (hasMapper(type)) {
-
throw
new BindingException(
"Type " + type +
" is already known to the MapperRegistry.");
-
}
-
boolean loadCompleted =
false;
-
try {
-
knownMappers.put(type,
new MapperProxyFactory<T>(type));
-
//加入到map中后立即解析mapper中的注解，目的是拿到mapper中的注解sql语句
-
// It's important that the type is added before the parser is run
-
// otherwise the binding may automatically be attempted by the
-
// mapper parser. If the type is already known, it won't try.
-
MapperAnnotationBuilder parser =
new MapperAnnotationBuilder(config, type);
-
parser.parse();
-
loadCompleted =
true;
-
}
finally {
-
if (!loadCompleted) {
-
knownMappers.remove(type);
-
}
-
}
-
}
-
}
-
-
-
public
class MapperProxyFactory<T> {
-
-
private
final Class<T> mapperInterface;
-
private
final Map<Method, MapperMethod> methodCache =
new ConcurrentHashMap<Method, MapperMethod>();
-
-
public MapperProxyFactory(Class<T> mapperInterface) {
-
this.mapperInterface = mapperInterface;
-
}
-
-
public Class<T> getMapperInterface() {
-
return mapperInterface;
-
}
-
-
public Map<Method, MapperMethod> getMethodCache() {
-
return methodCache;
-
}
-
-
//动态代理回调方法
-
@SuppressWarnings(
"unchecked")
-
protected T newInstance(MapperProxy<T> mapperProxy) {
-
return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(),
new Class[] { mapperInterface }, mapperProxy);
-
}
-
-
//mapper代理类的实例化方法
-
public T newInstance(SqlSession sqlSession) {
-
final MapperProxy<T> mapperProxy =
new MapperProxy<T>(sqlSession, mapperInterface, methodCache);
-
return newInstance(mapperProxy);
-
}
-
-
}
继续往下执行，同时注意控制台的输出情况，看到控制台输出一句Finished creating instance of bean 'userMapper'，此时mapper实例化完成，既然实例化完成了，那么就要返回实例化好的mapper，由于bd中放的beanClass是mapperFactoryBean，所以mapper实例要从mapperFactoryBean的getObject方法中来获得，来看代码
-
//org.mybatis.spring.mapper.MapperFactoryBean#getObject
-
@Override
-
public T getObject() throws Exception {
-
return getSqlSession().getMapper(
this.mapperInterface);
-
}
-
-
-
//org.mybatis.spring.SqlSessionTemplate#getMapper
-
//sqlSessionTemplate作为sqlSession
-
@Override
-
public <T>
T getMapper(Class<T> type) {
-
return getConfiguration().getMapper(type,
this);
-
}
-
-
//org.apache.ibatis.session.Configuration#getMapper
-
public <T>
T getMapper(Class<T> type, SqlSession sqlSession) {
-
return mapperRegistry.getMapper(type, sqlSession);
-
}
-
-
//org.apache.ibatis.binding.MapperRegistry#getMapper
-
public <T>
T getMapper(Class<T> type, SqlSession sqlSession) {
-
final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
-
if (mapperProxyFactory ==
null) {
-
throw
new BindingException(
"Type " + type +
" is not known to the MapperRegistry.");
-
}
-
try {
-
//之前说过，这里返回的是个代理的对象，也就是经过动态代理的mapper
-
return mapperProxyFactory.newInstance(sqlSession);
-
}
catch (Exception e) {
-
throw
new BindingException(
"Error getting mapper instance. Cause: " + e, e);
-
}
-
}
我们观察变量的变化，发现最终返回的object被MapperProxy所代理，到此为止，mapper已经被spring所管理，spring将通过动态代理技术使用代理类来执行mapper中的各种操作。
总结
经过自己动手用纯注解的方式整合spring和mybatis，我们看到了mybatis基于spring做的许多扩展，同时也看到了spring的很多扩展点，比如ImportBeanDefinitionRegistrar、InitializingBean、FactoryBean，下面总结一下mybatis整合spring过程中所用到的几个关键的类和这些类的基本功能
- ClassPathMapperScanner：继承Spring的ClassPathBeanDefinitionScanner，作用是在classPath中扫描mapper以及扫描之后处理beanDefinition，mapperFactoryBean在这个类中的processBeanDefinitions方法中被加入beanDefinition
- MapperFactoryBean：继承mybatis-spring的SqlSessionDaoSupport，实现了Spring的FactoryBean接口，作用是自定义bean，同时负责在mybatis的初始化结束之后添加mapper以及获取mapper的代理对象
- MapperRegistry：mapper注册器，添加和获取mapper的实际类
- MapperProxy：mapper代理类，调用invoke方法来执行代理方法代理实际mapper中的操作及缓存mapper中的method
- MapperMethod：mapper方法类，包含目标方法对象和sql命令对象，主要作用是执行目标方法的sql语句
- SqlSessionTemplate：mybatis整合spring的核心类，这个类控制sqlSession，包含一个内部类用来执行动态代理
转载：https://blog.csdn.net/wangjimmy1994/article/details/106771698
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