【Spring Boot】（29）、SpringBoot整合Mybatis原始碼分析
阿新 • • 發佈：2018-10-31
在【Spring Boot】（23）、Spring Boot整合Mybatis的章節中講述了SpringBoot整合Mybatis的過程，以及一些配置說明，這節主要講解一下整合的原始碼。
廢話不多說，直接進入今天的主題。
閱讀過我之前寫的文章的童靴，肯定知道SpringBoot整合第三方技術的時候，都會有一個xxxAutoConfiguration的自動配置類，咱們來一起找找看。其實在專案整合Mybatis的時候，需要依賴mybatis-spring-boot-starter包：
<dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>${mybatis.springboot.version}</version> </dependency>
依賴情況如下：
在mybatis-spring-boot-autoconfigure-xxx.jar包中可以找到META-INF/spring.factories的檔案，開啟後可以看到裡面的自動配置類：
# Auto Configure org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration
因此進入MybatisAutoConfiguration配置類中：
@org.springframework.context.annotation.Configuration @ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class }) @ConditionalOnBean(DataSource.class) @EnableConfigurationProperties(MybatisProperties.class) @AutoConfigureAfter(DataSourceAutoConfiguration.class) public class MybatisAutoConfiguration { private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class); private final MybatisProperties properties; private final Interceptor[] interceptors; private final ResourceLoader resourceLoader; private final DatabaseIdProvider databaseIdProvider; private final List<ConfigurationCustomizer> configurationCustomizers; public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider, ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider, ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) { this.properties = properties; this.interceptors = interceptorsProvider.getIfAvailable(); this.resourceLoader = resourceLoader; this.databaseIdProvider = databaseIdProvider.getIfAvailable(); this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable(); } @PostConstruct //在建構函式之後，初始化之前，載入mybatis的配置檔案 public void checkConfigFileExists() { if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) { Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation()); Assert.state(resource.exists(), "Cannot find config location: " + resource + " (please add config file or check your Mybatis configuration)"); } } @Bean @ConditionalOnMissingBean public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception { SqlSessionFactoryBean factory = new SqlSessionFactoryBean(); factory.setDataSource(dataSource); factory.setVfs(SpringBootVFS.class); if (StringUtils.hasText(this.properties.getConfigLocation())) { factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation())); } Configuration configuration = this.properties.getConfiguration(); if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) { configuration = new Configuration(); } if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) { for (ConfigurationCustomizer customizer : this.configurationCustomizers) { customizer.customize(configuration); } } factory.setConfiguration(configuration); if (this.properties.getConfigurationProperties() != null) { factory.setConfigurationProperties(this.properties.getConfigurationProperties()); } if (!ObjectUtils.isEmpty(this.interceptors)) { factory.setPlugins(this.interceptors); } if (this.databaseIdProvider != null) { factory.setDatabaseIdProvider(this.databaseIdProvider); } if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) { factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage()); } if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) { factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage()); } if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) { factory.setMapperLocations(this.properties.resolveMapperLocations()); } return factory.getObject(); } @Bean @ConditionalOnMissingBean public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { ExecutorType executorType = this.properties.getExecutorType(); if (executorType != null) { return new SqlSessionTemplate(sqlSessionFactory, executorType); } else { return new SqlSessionTemplate(sqlSessionFactory); } } //other code... }
在自動配置的時候會匯入一個Properties配置類MybatisProperties，咱們來看一下：
@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {
public static final String MYBATIS_PREFIX = "mybatis";
/**
* Location of MyBatis xml config file.
*/
private String configLocation;
/**
* Locations of MyBatis mapper files.
*/
private String[] mapperLocations;
/**
* Packages to search type aliases. (Package delimiters are ",; \t\n")
*/
private String typeAliasesPackage;
/**
* Packages to search for type handlers. (Package delimiters are ",; \t\n")
*/
private String typeHandlersPackage;
/**
* Indicates whether perform presence check of the MyBatis xml config file.
*/
private boolean checkConfigLocation = false;
/**
* Execution mode for {@link org.mybatis.spring.SqlSessionTemplate}.
*/
private ExecutorType executorType;
/**
* Externalized properties for MyBatis configuration.
*/
private Properties configurationProperties;
/**
* A Configuration object for customize default settings. If {@link #configLocation}
* is specified, this property is not used.
*/
@NestedConfigurationProperty
private Configuration configuration;
//other code...
}
該Properties配置類作用主要用於與yml/properties中以mybatis開頭的屬性進行一一對應，略過。
在MybatisAutoConfiguration自動配置類中，SpringBoot預設自動配置了兩個Bean，分別是SqlSessionFactory和SqlSessionTemplate。SqlSessionFactory主要是將Properties配置類中的屬性賦值到SqlSessionFactoryBean中，類似以前xml中配置的SqlSessionFactory：
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource"></property>
<!-- 自動掃描mapping.xml檔案 -->
<property name="mapperLocations" value="classpath:com/cn/mapper/*.xml"></property>
...
</bean>
其中在建立SqlSessionFactory的Bean中，有段程式碼：
if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
customizer.customize(configuration);
}
}
在【Spring Boot】（23）、Spring Boot整合Mybatis的章節中也講述了，通過實現Mybatis中的ConfigurationCustomizer介面，重寫customize方法，達到覆蓋Mybatis中的預設配置項的功能。
public interface ConfigurationCustomizer {
void customize(Configuration configuration);
}
引數Configuration即為Mybatis的配置項：
public class Configuration {
protected Environment environment;
protected boolean safeRowBoundsEnabled;
protected boolean safeResultHandlerEnabled = true;
protected boolean mapUnderscoreToCamelCase;
protected boolean aggressiveLazyLoading;
protected boolean multipleResultSetsEnabled = true;
protected boolean useGeneratedKeys;
protected boolean useColumnLabel = true;
protected boolean cacheEnabled = true;
protected boolean callSettersOnNulls;
protected boolean useActualParamName = true;
protected boolean returnInstanceForEmptyRow;
protected String logPrefix;
protected Class <? extends Log> logImpl;
protected Class <? extends VFS> vfsImpl;
protected LocalCacheScope localCacheScope = LocalCacheScope.SESSION;
protected JdbcType jdbcTypeForNull = JdbcType.OTHER;
protected Set<String> lazyLoadTriggerMethods = new HashSet<String>(Arrays.asList(new String[] { "equals", "clone", "hashCode", "toString" }));
protected Integer defaultStatementTimeout;
protected Integer defaultFetchSize;
protected ExecutorType defaultExecutorType = ExecutorType.SIMPLE;
protected AutoMappingBehavior autoMappingBehavior = AutoMappingBehavior.PARTIAL;
protected AutoMappingUnknownColumnBehavior autoMappingUnknownColumnBehavior = AutoMappingUnknownColumnBehavior.NONE;
protected Properties variables = new Properties();
protected ReflectorFactory reflectorFactory = new DefaultReflectorFactory();
protected ObjectFactory objectFactory = new DefaultObjectFactory();
protected ObjectWrapperFactory objectWrapperFactory = new DefaultObjectWrapperFactory();
protected boolean lazyLoadingEnabled = false;
protected ProxyFactory proxyFactory = new JavassistProxyFactory(); // #224 Using internal Javassist instead of OGNL
protected String databaseId;
/**
* Configuration factory class.
* Used to create Configuration for loading deserialized unread properties.
*
* @see <a href='https://code.google.com/p/mybatis/issues/detail?id=300'>Issue 300 (google code)</a>
*/
protected Class<?> configurationFactory;
protected final MapperRegistry mapperRegistry = new MapperRegistry(this);
protected final InterceptorChain interceptorChain = new InterceptorChain();
protected final TypeHandlerRegistry typeHandlerRegistry = new TypeHandlerRegistry();
protected final TypeAliasRegistry typeAliasRegistry = new TypeAliasRegistry();
protected final LanguageDriverRegistry languageRegistry = new LanguageDriverRegistry();
protected final Map<String, MappedStatement> mappedStatements = new StrictMap<MappedStatement>("Mapped Statements collection");
protected final Map<String, Cache> caches = new StrictMap<Cache>("Caches collection");
protected final Map<String, ResultMap> resultMaps = new StrictMap<ResultMap>("Result Maps collection");
protected final Map<String, ParameterMap> parameterMaps = new StrictMap<ParameterMap>("Parameter Maps collection");
protected final Map<String, KeyGenerator> keyGenerators = new StrictMap<KeyGenerator>("Key Generators collection");
protected final Set<String> loadedResources = new HashSet<String>();
protected final Map<String, XNode> sqlFragments = new StrictMap<XNode>("XML fragments parsed from previous mappers");
protected final Collection<XMLStatementBuilder> incompleteStatements = new LinkedList<XMLStatementBuilder>();
protected final Collection<CacheRefResolver> incompleteCacheRefs = new LinkedList<CacheRefResolver>();
protected final Collection<ResultMapResolver> incompleteResultMaps = new LinkedList<ResultMapResolver>();
protected final Collection<MethodResolver> incompleteMethods = new LinkedList<MethodResolver>();
//other code...
}
具體可以看看【Spring Boot】（23）、Spring Boot整合Mybatis中的使用方式，在此就不在講解了。
另外一個Bean為SqlSessionTemplate，通過SqlSessionFactory來生成SqlSession代理類：
public class SqlSessionTemplate implements SqlSession, DisposableBean {
private final SqlSessionFactory sqlSessionFactory;
private final ExecutorType executorType;
private final SqlSession sqlSessionProxy;
private final PersistenceExceptionTranslator exceptionTranslator;
//other code...
public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
PersistenceExceptionTranslator exceptionTranslator) {
notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
notNull(executorType, "Property 'executorType' is required");
this.sqlSessionFactory = sqlSessionFactory;
this.executorType = executorType;
this.exceptionTranslator = exceptionTranslator;
//生成SqlSessioin代理類
this.sqlSessionProxy = (SqlSession) newProxyInstance(
SqlSessionFactory.class.getClassLoader(),
new Class[] { SqlSession.class },
new SqlSessionInterceptor());
}
}
在MybatisAutoConfiguration自動配置類中，有個靜態內部類 AutoConfiguredMapperScannerRegistrar ：
public static class AutoConfiguredMapperScannerRegistrar
implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware {
private BeanFactory beanFactory;
private ResourceLoader resourceLoader;
@Override
public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
logger.debug("Searching for mappers annotated with @Mapper");
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
try {
if (this.resourceLoader != null) {
scanner.setResourceLoader(this.resourceLoader);
}
List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
if (logger.isDebugEnabled()) {
for (String pkg : packages) {
logger.debug("Using auto-configuration base package '{}'", pkg);
}
}
//新增@Mapper註解
scanner.setAnnotationClass(Mapper.class);
scanner.registerFilters();
//進行包掃描，載入新增@Mapper註解的類
scanner.doScan(StringUtils.toStringArray(packages));
} catch (IllegalStateException ex) {
logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex);
}
}
@Override
public void setBeanFactory(BeanFactory beanFactory) throws BeansException {
this.beanFactory = beanFactory;
}
@Override
public void setResourceLoader(ResourceLoader resourceLoader) {
this.resourceLoader = resourceLoader;
}
}
@org.springframework.context.annotation.Configuration
@Import({ AutoConfiguredMapperScannerRegistrar.class })
@ConditionalOnMissingBean(MapperFactoryBean.class)
public static class MapperScannerRegistrarNotFoundConfiguration {
@PostConstruct
public void afterPropertiesSet() {
logger.debug("No {} found.", MapperFactoryBean.class.getName());
}
}
它主要用於掃描帶有@Mapper註解的mapper介面，暫時先不講這個內部類，後面再講。
咱們先來講下Mybatis的MapperScannerRegistrar，它的功能同上述功能剛好相反。學過SpringBoot整合Mybatis的童靴，肯定知道一個註解@MapperScan，來看看它的簽名：
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {
//other code...
}
可以看到，如果使用了@MapperScan註解，則專案會匯入MapperScannerRegistrar：
public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware {
private ResourceLoader resourceLoader;
@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>();
//解析@MapperScan的屬性
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();
//進行包掃描
scanner.doScan(StringUtils.toStringArray(basePackages));
}
@Override
public void setResourceLoader(ResourceLoader resourceLoader) {
this.resourceLoader = resourceLoader;
}
}
一旦使用@MapperScan註解，則回在MapperScannerRegistrar#registerBeanDefinitions方法中會解析@MapperScan註解的屬性，載入basePackages，並進行包掃描，呼叫doScan方法。
public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {
//other code...
private MapperFactoryBean<?> mapperFactoryBean = new MapperFactoryBean<Object>();
@Override
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
//呼叫父類的doScan方法
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 {
//進行Bean定義
processBeanDefinitions(beanDefinitions);
}
return beanDefinitions;
}
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());
//將@MapperScan掃描進來的Mapper介面的class設定為MapperFactoryBean的class
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() + "'.");
}
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
}
}
}
重點程式碼：
definition.setBeanClass(this.mapperFactoryBean.getClass());
從這句程式碼可以看到，在MapperScannerRegistrar中，把@MapperScan包掃描進來的Mapper介面的class設定成來MapperFactoryBean的class，所以使用@MapperScan註解的話，在容器中就存在MapperFactoryBean這個型別的Bean，從而導致MapperScannerRegistrarNotFoundConfiguration配置類不生效，原因就是類簽名上有個註解@ConditionalOnMissingBean(MapperFactoryBean.class)。
既然如果使用了@MapperScan註解會導致AutoConfiguredMapperScannerRegistrar(MapperScannerRegistrarNotFoundConfiguration)不生效，那麼只要去掉@MapperScan註解，自然就會進入AutoConfiguredMapperScannerRegistrar這個匯入類了，重點來了：
//預設為Application主類所在的包及其子包
List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
//設定掃描器的掃描類型別，帶有@Mapper註解的類
scanner.setAnnotationClass(Mapper.class);
scanner.registerFilters();
//進行包掃描
scanner.doScan(StringUtils.toStringArray(packages));
最後Mybatis的CRUD操作都是通過SqlSessionTemplate這個代理例項進行操作。
吐槽一下：
好久沒寫部落格了，發現csdn部落格大變樣，什麼左對齊啊，背景色啊，都沒了，真不習慣。
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