【1】pom文件添加依赖
依赖如下所示：
<dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-web</artifactId> </dependency> <!--mybatis--> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.3.1</version> </dependency> <!-- mysql-connector-java--> <dependency> <groupId>mysql</groupId> <artifactId>mysql-connector-java</artifactId> <scope>runtime</scope> </dependency> <!-- https://mvnrepository.com/artifact/com.alibaba/druid --> <dependency> <groupId>com.alibaba</groupId> <artifactId>druid</artifactId> <version>1.1.10</version> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-test</artifactId> <scope>test</scope> </dependency>
【2】配置数据源，数据库建立表，并生成pojo
数据源配置
spring: datasource: url: jdbc:mysql://localhost:3306/test username: root password: 123456 driver-class-name: com.mysql.jdbc.Driver type: com.alibaba.druid.pool.DruidDataSource initialSize: 5 minIdle: 5 maxActive: 20 maxWait: 60000 timeBetweenEvictionRunsMillis: 60000 minEvictableIdleTimeMillis: 300000 validationQuery: SELECT 1 FROM DUAL testWhileIdle: true testOnBorrow: true testOnReturn: false poolPreparedStatements: true # 配置监控统计拦截的filters，去掉后监控界面sql无法统计，'wall'用于防火墙 filters: stat,wall,log4j maxPoolPreparedStatementPerConnectionSize: 20 useGlobalDataSourceStat: true connectionProperties: druid.stat.mergeSql=true;druid.stat.slowSqlMillis=500
两个JavaBean
这里使用两个类，department和employee
Department源码如下：
public class Department implements Serializable { private Integer id; private String departmentName; public void setId(Integer id) { this.id = id; } public void setDepartmentName(String departmentName) { this.departmentName = departmentName; } public Integer getId() { return id; } public String getDepartmentName() { return departmentName; } }
Employee源码如下：
public class Employee implements Serializable { private Integer id; private String lastName; private Integer gender; private String email; private Integer dId; public void setId(Integer id) { this.id = id; } public void setLastName(String lastName) { this.lastName = lastName; } public void setGender(Integer gender) { this.gender = gender; } public void setEmail(String email) { this.email = email; } public void setdId(Integer dId) { this.dId = dId; } public Integer getId() { return id; } public String getLastName() { return lastName; } public Integer getGender() { return gender; } public String getEmail() { return email; } public Integer getdId() { return dId; } }
【3】编写注解版的Mapper
DepartmentMapper 源码
//指定这是一个操作数据库的mapper @Mapper public interface DepartmentMapper { @Select("select id,department_name as departmentName from department where id=#{id}") public Department getDeptById(Integer id); @Delete("delete from department where id=#{id}") public int deleteDeptById(Integer id); @Options(useGeneratedKeys = true,keyProperty = "id") @Insert("insert into department(department_name) values(#{departmentName})") public int insertDept(Department department); @Update("update department set department_name=#{departmentName} where id=#{id}") public int updateDept(Department department); }
EmployeeMapper源码
//@Mapper或者@MapperScan将接口扫描装配到容器中 public interface EmployeeMapper { @Select("select * from employee where id=#{id}") public Employee getEmpById(Integer id); @Insert("insert into employee(lastName,email,gender,d_id) values(#{lastName},#{email},#{gender},#{dId})") public void insertEmp(Employee employee); }
注意事项
第一对象的属性与数据表列属性不完全一直，如department的departmentName与数据表中department_name列对应。
解决方法：
- ① SQL中使用别名方式；
- ② 向容器中注册自定义的ConfigurationCustomizer
@org.springframework.context.annotation.Configuration public class MyBatisConfig { @Bean public ConfigurationCustomizer configurationCustomizer(){ return new ConfigurationCustomizer(){ @Override public void customize(Configuration configuration) { //这里表示开启驼峰命名 configuration.setMapUnderscoreToCamelCase(true); } }; } }
第二，数据表中department的id为自增，则默认情况下插入department后，department对象的id为null(数据表有值，id列为自增),如下图所示：
解决办法如下：添加@Options注解
@Options(useGeneratedKeys = true,keyProperty = "id") @Insert("insert into department(department_name) values(#{departmentName})") public int insertDept(Department department);
编写Controller进行简单测试
DeptController 源码如下：
@RestController public class DeptController { @Autowired DepartmentMapper departmentMapper; @RequestMapping("/dept/{id}") public Department getDepartment(@PathVariable("id") Integer id){ return departmentMapper.getDeptById(id); } @GetMapping("/dept") public Department insertDept(Department department){ departmentMapper.insertDept(department); System.out.println(department); return department; } }
【4】@MapperScan注解
配置该注解后即可不用在每个mapper上面添加注解，示例如下：
@org.springframework.context.annotation.Configuration @MapperScan(basePackages = {"com.springboot.datasource.mapper"}) public class MyBatisConfig { @Bean public ConfigurationCustomizer configurationCustomizer(){ return new ConfigurationCustomizer(){ @Override public void customize(Configuration configuration) { configuration.setMapUnderscoreToCamelCase(true); } }; } }
注解源码与说明
在Java配置类上面使用该注解可以注册Mybatis mapper接口，效果等同于通过MapperScannerRegistrar注册的MapperScannerConfigurer。
配置实例如下：
@Configuration @MapperScan("org.mybatis.spring.sample.mapper") public class AppConfig { @Bean public DataSource dataSource() { return new EmbeddedDatabaseBuilder() .addScript("schema.sql") .build(); } @Bean public DataSourceTransactionManager transactionManager() { return new DataSourceTransactionManager(dataSource()); } @Bean public SqlSessionFactory sqlSessionFactory() throws Exception { SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean(); sessionFactory.setDataSource(dataSource()); return sessionFactory.getObject(); } }
源码如下
@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) @Documented @Import(MapperScannerRegistrar.class) public @interface MapperScan { //basePackages 的别名，更简洁的注解声明，如下所示 //* @EnableMyBatisMapperScanner("org.my.pkg")} //* @EnableMyBatisMapperScanner(basePackages= "org.my.pkg"}) String[] value() default {}; //MyBatis接口的基础包 String[] basePackages() default {}; //一种类型安全的选择，效果等同于basePackages Class<?>[] basePackageClasses() default {}; //指定BeanNameGenerator Class<? extends BeanNameGenerator> nameGenerator() default BeanNameGenerator.class; //指定base package下的包含的注解的类，可以与markerInterface联合使用 Class<? extends Annotation> annotationClass() default Annotation.class; //指定需要扫描注册的接口 ，可以与注解配置使用 Class<?> markerInterface() default Class.class; //当你有多个数据源的时候，这里指定你需要哪个SqlSessionTemplate String sqlSessionTemplateRef() default ""; //当你有多个数据源的时候,这里指定你需要哪个SqlSessionFactory String sqlSessionFactoryRef() default ""; //指定一个自定义的MapperFactoryBean(该bean用来生成mybatis proxy bean) Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class; }
【5】MyBatis的自动配置
如下图所示，添加后mybatis-spring-boot-starter依赖如下图：
其中MyBatis的自动配置如下图：
在类MybatisAutoConfiguration 注册了许多以前我们在XML中配置的bean，如SqlSessionFactory。
MybatisAutoConfiguration 源码
@Configuration @ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class}) @ConditionalOnBean({DataSource.class}) //MyBatis的属性对应类 @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 = (Interceptor[])interceptorsProvider.getIfAvailable(); this.resourceLoader = resourceLoader; this.databaseIdProvider = (DatabaseIdProvider)databaseIdProvider.getIfAvailable(); this.configurationCustomizers = (List)configurationCustomizersProvider.getIfAvailable(); } @PostConstruct 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)"); } } //... }
解释如下：
- 使用properties、interceptors 、resourceLoader 、databaseIdProvider 以及configurationCustomizers 创建MybatisAutoConfiguration
- checkConfigFileExists，检测配置文件是否存在
@PostConstruct
@PostConstruct注解作用在方法上，在依赖注入完成后进行一些初始化操作。这个方法在类被放入service之前被调用，所有支持依赖项注入的类都必须支持此注解。
注册SqlSessionFactory
@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())); } org.apache.ibatis.session.Configuration configuration = this.properties.getConfiguration(); if(configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) { configuration = new org.apache.ibatis.session.Configuration(); } if(configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) { Iterator var4 = this.configurationCustomizers.iterator(); while(var4.hasNext()) { ConfigurationCustomizer customizer = (ConfigurationCustomizer)var4.next(); 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(); }
代码解释如下：
- 创建SqlSessionFactoryBean实例
- 设置dataSource
- 设置SpringBootVFS
- 设置ConfigLocation
- 设置configuration
- 设置ConfigurationProperties
- 设置.Plugins(this.interceptors)
- 设置DatabaseIdProvider
- 设置TypeAliasesPackage
- 设置TypeHandlersPackage
- 设置MapperLocations
- 获取SqlSessionFactory(factory.getObject())
注册SqlSessionTemplate
@Bean @ConditionalOnMissingBean public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { ExecutorType executorType = this.properties.getExecutorType(); return executorType != null?new SqlSessionTemplate(sqlSessionFactory, executorType):new SqlSessionTemplate(sqlSessionFactory); }
根据sqlSessionFactory和executorType创建SqlSessionTemplate实例。SqlSessionTemplate是spring提供的一个线程安全的sqlSession管理工具，可以管理session的生命周期包括提交、回滚以及关闭session。
AutoConfiguredMapperScannerRegistrar
@Configuration @Import({MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar.class}) @ConditionalOnMissingBean({MapperFactoryBean.class}) public static class MapperScannerRegistrarNotFoundConfiguration { public MapperScannerRegistrarNotFoundConfiguration() { } @PostConstruct public void afterPropertiesSet() { MybatisAutoConfiguration.logger.debug("No {} found.", MapperFactoryBean.class.getName()); } } public static class AutoConfiguredMapperScannerRegistrar implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware { private BeanFactory beanFactory; private ResourceLoader resourceLoader; public AutoConfiguredMapperScannerRegistrar() { } public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { MybatisAutoConfiguration.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(MybatisAutoConfiguration.logger.isDebugEnabled()) { Iterator var5 = packages.iterator(); while(var5.hasNext()) { String pkg = (String)var5.next(); MybatisAutoConfiguration.logger.debug("Using auto-configuration base package '{}'", pkg); } } scanner.setAnnotationClass(Mapper.class); scanner.registerFilters(); scanner.doScan(StringUtils.toStringArray(packages)); } catch (IllegalStateException var7) { MybatisAutoConfiguration.logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", var7); } } //... } }
【6】注解开启二级缓存
Spring与MyBatis整合时，MyBatis的一级缓存在没有事务存在的时候失效。
在未开启事务的情况之下，每次查询，spring都会关闭旧的sqlSession而创建新的sqlSession,因此此时的一级缓存是没有启作用的;
在开启事务的情况之下，spring使用threadLocal获取当前资源绑定同一个sqlSession，因此此时一级缓存是有效的。
配置实例与测试
SpringBoot中默认帮我们全局开启了二级缓存，如果想要使用二级缓存还需要在mapper上注明。
源码示例如下：
@CacheNamespace public interface EmployeeMapper { @Select("select * from employee where id=#{id}") public Employee getEmpById(Integer id); @Insert("insert into employee(lastName,email,gender,d_id) values(#{lastName},#{email},#{gender},#{dId})") public void insertEmp(Employee employee); }
这里使用@CacheNamespace注解(为给定的命名空间（比如类）配置缓存，对应xml<cache>)在该mapper上使用二级缓存。
<mapper namespace="xxx.***.EmployeeMapper "> <cache/> </mapper>
连续发起两次查询语句，查询同一个id的Employee，控制台日志如下：
@CacheNamespace源码
@Documented @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) public @interface CacheNamespace { /** mybatis的一级缓存，默认情况下都处于开启状态，只能使用自带的PerpetualCache，无法配置第三方缓存； mybatis的二级缓存，可以配置开关状态，默认使用自带的PerpetualCache，但功能比较弱，能够配置第三方缓存。 */ Class<? extends org.apache.ibatis.cache.Cache> implementation() default PerpetualCache.class; //回收策略--最近最少使用 Class<? extends org.apache.ibatis.cache.Cache> eviction() default LruCache.class; long flushInterval() default 0; int size() default 1024; boolean readWrite() default true; boolean blocking() default false; //为实现类提供Property 配置，3.4.2+版本支持 Property[] properties() default {}; }
【7】MyBatis中Cache解析处理过程
如下图所示：
通过源码查看MyBatis中二级缓存的默认配置如下。
XMLMapperBuilder.cacheElement:
private void cacheElement(XNode context) throws Exception { if (context != null) { //获取配置的type值，默认值为PERPETUAL String type = context.getStringAttribute("type", "PERPETUAL"); //获取type的class Class<? extends Cache> typeClass = typeAliasRegistry.resolveAlias(type); //获取配置过期策略，默认值为LRU String eviction = context.getStringAttribute("eviction", "LRU"); Class<? extends Cache> evictionClass = typeAliasRegistry.resolveAlias(eviction); //获取配置的刷新间隔 Long flushInterval = context.getLongAttribute("flushInterval"); //获取配置的缓存大小 Integer size = context.getIntAttribute("size"); //是否配置了只读，默认为false boolean readWrite = !context.getBooleanAttribute("readOnly", false); //是否配置了阻塞，默认为false boolean blocking = context.getBooleanAttribute("blocking", false); Properties props = context.getChildrenAsProperties(); builderAssistant.useNewCache(typeClass, evictionClass, flushInterval, size, readWrite, blocking, props); } }
MapperBuilderAssistant.useNewCache:
public Cache useNewCache(Class<? extends Cache> typeClass, Class<? extends Cache> evictionClass, Long flushInterval, Integer size, boolean readWrite, boolean blocking, Properties props) { Cache cache = new CacheBuilder(currentNamespace) .implementation(valueOrDefault(typeClass, PerpetualCache.class)) .addDecorator(valueOrDefault(evictionClass, LruCache.class)) .clearInterval(flushInterval) .size(size) .readWrite(readWrite) .blocking(blocking) .properties(props) .build(); configuration.addCache(cache); currentCache = cache; return cache; }
Cache支持的过期策略：
typeAliasRegistry.registerAlias("FIFO", FifoCache.class); typeAliasRegistry.registerAlias("LRU", LruCache.class); typeAliasRegistry.registerAlias("SOFT", SoftCache.class); typeAliasRegistry.registerAlias("WEAK", WeakCache.class);
PerpetualCache缓存实现源码：
public class PerpetualCache implements Cache { //缓存ID private final String id; //缓存 private Map<Object, Object> cache = new HashMap<Object, Object>(); public PerpetualCache(String id) { this.id = id; } @Override public String getId() { return id; } @Override public int getSize() { return cache.size(); } @Override public void putObject(Object key, Object value) { cache.put(key, value); } @Override public Object getObject(Object key) { return cache.get(key); } @Override public Object removeObject(Object key) { return cache.remove(key); } @Override public void clear() { cache.clear(); } @Override public ReadWriteLock getReadWriteLock() { return null; } @Override public boolean equals(Object o) { if (getId() == null) { throw new CacheException("Cache instances require an ID."); } if (this == o) { return true; } if (!(o instanceof Cache)) { return false; } Cache otherCache = (Cache) o; return getId().equals(otherCache.getId()); } @Override public int hashCode() { if (getId() == null) { throw new CacheException("Cache instances require an ID."); } return getId().hashCode(); } }
【8】高版本中url和驱动不同
在SpringBoot2.0等更高版本时，如果MySQL驱动使用的是8版本，那么可能会出现如下异常：
java.sql.SQLException: The server time zone value 'Öйú±ê׼ʱ¼ä' is unrecognized
并且还可能提示你驱动需要更换为如下：
com.mysql.cj.jdbc.Driver
此时只需要更改为如下则可：
spring.datasource.url=jdbc:mysql://localhost:3306/test?serverTimezone=GMT%2B8 spring.datasource.username=root spring.datasource.password=123456 spring.datasource.driver-class-name=com.mysql.cj.jdbc.Driver
