MyBatis的基本应用

源码地址

01.MyBatis环境搭建

添加MyBatis的坐标

        <!--mybatis坐标--><dependency><groupId>org.mybatis</groupId><artifactId>mybatis</artifactId><version>3.5.9</version></dependency><!--mysql驱动坐标--><dependency><groupId>mysql</groupId><artifactId>mysql-connector-java</artifactId><version>8.0.33</version><scope>runtime</scope></dependency><!--单元测试坐标--><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.13.2</version></dependency>

创建数据表
编写DO实体类

编写映射⽂件UserMapper.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.muchfish.dao.IUserDao"><!--namespace : 名称空间：与id组成sql的唯一标识resultType： 表明返回值类型--><!--查询用户--><select id="findAll" resultType="com.muchfish.pojo.User">select * from User</select></mapper>

编写核⼼⽂件SqlMapConfig.xml

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN""http://mybatis.org/dtd/mybatis-3-config.dtd"><configuration><!--加载外部的properties文件--><properties resource="jdbc.properties"/><!--environments:运行环境--><environments default="development"><environment id="development"><!--当前事务交由JDBC进行管理--><transactionManager type="JDBC"/><!--当前使用mybatis提供的连接池--><dataSource type="POOLED"><property name="driver" value="${jdbc.driver}"/><property name="url" value="${jdbc.url}"/><property name="username" value="${jdbc.username}"/><property name="password" value="${jdbc.password}"/></dataSource></environment></environments><!--引入映射配置文件--><mappers><mapper resource="UserMapper.xml"/></mappers></configuration>

jdbc.properties

jdbc.driver=com.mysql.cj.jdbc.Driver
jdbc.url=jdbc:mysql:///mybatis
jdbc.username=root
jdbc.password=123456

编写测试类

    @Testpublic void test1() throws IOException {//1.Resources工具类，配置文件的加载，把配置文件加载成字节输入流InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");//2.解析了配置文件，并创建了sqlSessionFactory工厂SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);//3.生产sqlSessionSqlSession sqlSession = sqlSessionFactory.openSession();// 默认开启一个事务，但是该事务不会自动提交//在进行增删改操作时，要手动提交事务//4.sqlSession调用方法：查询所有selectList  查询单个：selectOne 添加：insert  修改：update 删除：deleteList<User> users = sqlSession.selectList("com.muchfish.dao.IUserDao.findAll");for (User user : users) {System.out.println(user);}sqlSession.close();}

02.MyBatis的CRUD

CRUD的API
- sqlSession.selectList()、sqlSession.selectOne()
- sqlSession.insert()
- sqlSession.update()
- sqlSession.delete()
注意问题
- 在进行增删改操作时，要手动提交事务。
  
  sqlSessionFactory.openSession()默认开启一个事务，但是该事务不会自动提交
- mapper.xml中的Sql语句中使⽤#{任意字符串}⽅式引⽤传递的单个参数
```

<delete id="deleteUser" parameterType="int">delete from user where id = #{abc}
</delete>
```
- sqlSession.close()：释放资源
- sqlSession.commit()
- sqlSession.rollback()
- sqlSessionFactory.openSession(true)：事务自动提交

03.MyBatis相关配置文件

sqlMapConfig.xml

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mapper标签

该标签的作⽤是加载映射的，加载⽅式有如下⼏种：

•使⽤相对于类路径的资源引⽤，例如：
<mapper resource="org/mybatis/builder/AuthorMapper.xml"/>•使⽤完全限定资源定位符（URL），例如：
<mapper url="file:///var/mappers/AuthorMapper.xml"/>•使⽤映射器接⼝实现类的完全限定类名，例如：
<mapper class="org.mybatis.builder.AuthorMapper"/>
注意：保证接口名和xml文件名一致且包结构一致（是否包结构一直皆可，文件名可以不一致）•将包内的映射器接⼝实现全部注册为映射器，例如：
<package name="org.mybatis.builder"/>
注意：保证接口名和xml文件名一致且包结构一致。（是否包结构一直皆可，文件名可以不一致。测试得：文件名也必须一致）

XXXmapper.xml

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04.MyBatis的Dao层代理开发方式与mappers标签测试

mappers标签测试

•使⽤映射器接⼝实现类的完全限定类名，例如：
<mapper class="com.muchfish.dao.IUserDao"/>
注意：保证接口名和xml文件名一致且包结构一致•将包内的映射器接⼝实现全部注册为映射器，例如：
<package name="com.muchfish.dao"/>
注意：保证接口名和xml文件名一致且包结构一致。

在这里插入图片描述

Dao层代理开发

Mapper 接⼝开发需要遵循以下规范：

Mapper.xml⽂件中的namespace与mapper接⼝的全限定名相同
Mapper接⼝⽅法名和Mapper.xml中定义的每个statement的id相同
Mapper接⼝⽅法的输⼊参数类型和mapper.xml中定义的每个sql的parameterType的类型相同
Mapper接⼝⽅法的输出参数类型和mapper.xml中定义的每个sql的resultType的类型相同

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05.MyBatis的多对多复杂映射

DO类

public class User {private Integer id;private String username;private String password;private String birthday;//表示用户关联的角色private List<Role> roleList = new ArrayList<>();//。。。省略getter/setter
}

Mapper.xml

    <resultMap id="userRoleMap" type="com.muchfish.pojo.User"><result property="id" column="userid"></result><result property="username" column="username"></result><collection property="roleList" ofType="com.muchfish.pojo.Role"><result property="id" column="roleid"></result><result property="roleName" column="roleName"></result><result property="roleDesc" column="roleDesc"></result></collection></resultMap><select id="findAllUserAndRole" resultMap="userRoleMap">select * from user u left join sys_user_role ur on u.id = ur.useridleft join sys_role r on r.id = ur.roleid</select>

Dao接口

public interface IUserDao {public List<User> findAllUserAndRole();
}

06.MyBatis的注解开发

MyBatis的常⽤注解
- @Insert：实现新增
- @Update：实现更新
- @Delete：实现删除
- @Select：实现查询
- @Result：实现结果集封装
- @Results：可以与@Result ⼀起使⽤，封装多个结果集
- @One：实现⼀对⼀结果集封装
- @Many：实现⼀对多结果集封装

注解一对多查询

public interface IOrderDao {//查询订单的同时还查询该订单所属的用户@Results({@Result(property = "id",column = "id"),@Result(property = "orderTime",column = "orderTime"),@Result(property = "total",column = "total"),@Result(property = "user",column = "uid",javaType = User.class,one=@One(select = "com.muchfish.dao.IUserDao.findUserById"))})@Select("select * from orders")public List<Order> findOrderAndUser();@Select("select * from orders where uid = #{uid}")public List<Order> findOrderByUid(Integer uid);}

注解和xml混合使用命中同一个statementId会报错

07.MyBatis缓存

⼀级缓存

private IUserDao userMapper;
private SqlSession sqlSession;
private SqlSessionFactory sqlSessionFactory;@Before
public void before() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);sqlSession = sqlSessionFactory.openSession();userMapper = sqlSession.getMapper(IUserDao.class);}@Test
public void test1() {//第⼀次查询，发出sql语句，并将查询出来的结果放进缓存中User u1 = userMapper.findUserById(1);System.out.println(u1);//第⼆次查询，由于是同⼀个sqlSession,会在缓存中查询结果//如果有，则直接从缓存中取出来，不和数据库进⾏交互User u2 = userMapper.findUserById(1);System.out.println(u2);sqlSession.close();
}

查看控制台打印情况：

在这里插入图片描述

    @Testpublic void test2(){//根据 sqlSessionFactory 产⽣ session//第⼀次查询，发出sql语句，并将查询的结果放⼊缓存中User u1 = userMapper.findUserById( 1 );System.out.println(u1);//第⼆步进⾏了⼀次更新操作， sqlSession.commit()u1.setPassword("23131");userMapper.updateUserByUserId(u1);sqlSession.commit();//第⼆次查询，由于是同⼀个sqlSession.commit(),会清空缓存信息//则此次查询也会发出sql语句User u2 = userMapper.findUserById(1);System.out.println(u2);sqlSession.close();}

查看控制台打印情况：
日志略：第⼆次查询会打印sql语句

在这里插入图片描述

总结
1. 第⼀次发起查询⽤户id为1的⽤户信息，先去找缓存中是否有id为1的⽤户信息，如果没有，从数据库查询⽤户信息。得到⽤户信息，将⽤户信息存储到⼀级缓存中。
2. 如果中间sqlSession去执⾏commit操作（执⾏插⼊、更新、删除），则会清空SqlSession中的⼀级缓存，这样做的⽬的为了让缓存中存储的是最新的信息，避免脏读。
3. 第⼆次发起查询⽤户id为1的⽤户信息，先去找缓存中是否有id为1的⽤户信息，缓存中有，直接从缓存中获取⽤户信息

二级缓存

在这里插入图片描述

使用二级缓存

开启⼆级缓存

在全局配置⽂件sqlMapConfig.xml⽂件中开启

<!--开启⼆级缓存 注意<settings>标签的顺序，在<properties>标签后面-->
<settings>
<setting name="cacheEnabled" value="true"/>
</settings>

在Mapper.xml⽂件中开启缓存

    <!--使用二级缓存--><cache></cache>

在DAO接口中开启缓存（可选。使用@CacheNamespace会报错。）
```
@CacheNamespace
public interface IUserDao {}
```
或
```
@CacheNamespaceRef(IUserDao.class) 
//@CacheNamespace
public interface IUserDao {}
```
- xml和对应dao接口上同时开启二级缓存会报错，此时只能使用@CacheNamespaceRef

DO序列化

public class User implements Serializable {//。。。
}

测试

 @Testpublic void SecondLevelCache(){//根据 sqlSessionFactory 产⽣ sessionSqlSession sqlSession1 = sqlSessionFactory.openSession();SqlSession sqlSession2 = sqlSessionFactory.openSession();SqlSession sqlSession3 = sqlSessionFactory.openSession();String statement = "com.lagou.pojo.UserMapper.selectUserByUserld" ;IUserDao userMapper1 = sqlSession1.getMapper(IUserDao. class );IUserDao userMapper2 = sqlSession2.getMapper(IUserDao. class );IUserDao userMapper3 = sqlSession2.getMapper(IUserDao. class );//第⼀次查询，发出sql语句，并将查询的结果放⼊缓存中User u1 = userMapper1.findById( 1 );System.out.println(u1);sqlSession1.close(); //第⼀次查询完后关闭sqlSession//执⾏更新操作， commit()。注释掉此处，sqlSession2的查询会走缓存。放开此处，会走数据库
//        u1.setUsername( "aaa" );
//        userMapper3.updateUserByUserId(u1);
//        sqlSession3.commit();//第⼆次查询，由于上次更新操作，缓存数据已经清空(防⽌数据脏读)，这⾥必须再次发出sql语User u2 = userMapper2.findById( 1 );System.out.println(u2);sqlSession2.close();}

useCache和flushCache

useCache：开启或禁用缓存

    <select id="findById" resultType="com.muchfish.pojo.User" useCache="true">select * from user where id = #{id}</select>

flushCache：刷新缓存

    <select id="findById" resultType="com.muchfish.pojo.User" useCache="true" flushCache="true">select * from user where id = #{id}</select>

二级缓存整合redis

pom⽂件

        <dependency><groupId>org.mybatis.caches</groupId><artifactId>mybatis-redis</artifactId><version>1.0.0-beta2</version></dependency>

配置⽂件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapperPUBLIC "-//mybatis.org//DTD Mapper 3.0//EN""http://mybatis.org/dtd/mybatis-3-mapper.dtd"><mapper namespace="com.muchfish.dao.IUserDao"><!--namespace : 名称空间：与id组成sql的唯一标识resultType： 表明返回值类型--><!--使用二级缓存--><cache type="org.mybatis.caches.redis.RedisCache" />

redis.properties

redis.host=localhost
redis.port=6379
redis.connectionTimeout=5000
redis.password=
redis.database=0

测试

    @Testpublic void xmlSecondLevelCache(){//根据 sqlSessionFactory 产⽣ sessionSqlSession sqlSession1 = sqlSessionFactory.openSession();SqlSession sqlSession2 = sqlSessionFactory.openSession();SqlSession sqlSession3 = sqlSessionFactory.openSession();String statement = "com.lagou.pojo.UserMapper.selectUserByUserld" ;IUserDao userMapper1 = sqlSession1.getMapper(IUserDao. class );IUserDao userMapper2 = sqlSession2.getMapper(IUserDao. class );IUserDao userMapper3 = sqlSession2.getMapper(IUserDao. class );//第⼀次查询，发出sql语句，并将查询的结果放⼊缓存中User u1 = userMapper1.findById( 1 );System.out.println(u1);sqlSession1.close(); //第⼀次查询完后关闭sqlSession//执⾏更新操作， commit()。注释掉此处，sqlSession2的查询会走缓存。放开此处，会走数据库
//        u1.setUsername( "aaa" );
//        userMapper3.updateUserByUserId(u1);
//        sqlSession3.commit();//第⼆次查询，由于上次更新操作，缓存数据已经清空(防⽌数据脏读)，这⾥必须再次发出sql语User u2 = userMapper2.findById( 1 );System.out.println(u2);sqlSession2.close();}

RedisCache实现原理

/*** Cache adapter for Redis.** @author Eduardo Macarron*/
public final class RedisCache implements Cache {private final ReadWriteLock readWriteLock = new DummyReadWriteLock();private String id;private static JedisPool pool;public RedisCache(final String id) {if (id == null) {throw new IllegalArgumentException("Cache instances require an ID");}this.id = id;RedisConfig redisConfig = RedisConfigurationBuilder.getInstance().parseConfiguration();pool = new JedisPool(redisConfig, redisConfig.getHost(), redisConfig.getPort(),redisConfig.getConnectionTimeout(), redisConfig.getSoTimeout(), redisConfig.getPassword(),redisConfig.getDatabase(), redisConfig.getClientName());}private Object execute(RedisCallback callback) {Jedis jedis = pool.getResource();try {return callback.doWithRedis(jedis);} finally {jedis.close();}}@Overridepublic String getId() {return this.id;}@Overridepublic int getSize() {return (Integer) execute(new RedisCallback() {@Overridepublic Object doWithRedis(Jedis jedis) {Map<byte[], byte[]> result = jedis.hgetAll(id.toString().getBytes());return result.size();}});}@Overridepublic void putObject(final Object key, final Object value) {execute(new RedisCallback() {@Overridepublic Object doWithRedis(Jedis jedis) {jedis.hset(id.toString().getBytes(), key.toString().getBytes(), SerializeUtil.serialize(value));return null;}});}@Overridepublic Object getObject(final Object key) {return execute(new RedisCallback() {@Overridepublic Object doWithRedis(Jedis jedis) {return SerializeUtil.unserialize(jedis.hget(id.toString().getBytes(), key.toString().getBytes()));}});}@Overridepublic Object removeObject(final Object key) {return execute(new RedisCallback() {@Overridepublic Object doWithRedis(Jedis jedis) {return jedis.hdel(id.toString(), key.toString());}});}@Overridepublic void clear() {execute(new RedisCallback() {@Overridepublic Object doWithRedis(Jedis jedis) {jedis.del(id.toString());return null;}});}@Overridepublic ReadWriteLock getReadWriteLock() {return readWriteLock;}@Overridepublic String toString() {return "Redis {" + id + "}";}}


/*** Converter from the Config to a proper {@link RedisConfig}.** @author Eduardo Macarron*/
final class RedisConfigurationBuilder {/*** This class instance.*/private static final RedisConfigurationBuilder INSTANCE = new RedisConfigurationBuilder();private static final String SYSTEM_PROPERTY_REDIS_PROPERTIES_FILENAME = "redis.properties.filename";private static final String REDIS_RESOURCE = "redis.properties";private final String redisPropertiesFilename;/*** Hidden constructor, this class can't be instantiated.*/private RedisConfigurationBuilder() {redisPropertiesFilename = System.getProperty(SYSTEM_PROPERTY_REDIS_PROPERTIES_FILENAME, REDIS_RESOURCE);}/*** Return this class instance.** @return this class instance.*/public static RedisConfigurationBuilder getInstance() {return INSTANCE;}/*** Parses the Config and builds a new {@link RedisConfig}.** @return the converted {@link RedisConfig}.*/public RedisConfig parseConfiguration() {return parseConfiguration(getClass().getClassLoader());}/*** Parses the Config and builds a new {@link RedisConfig}.** @param the*            {@link ClassLoader} used to load the*            {@code memcached.properties} file in classpath.* @return the converted {@link RedisConfig}.*/public RedisConfig parseConfiguration(ClassLoader classLoader) {Properties config = new Properties();InputStream input = classLoader.getResourceAsStream(redisPropertiesFilename);if (input != null) {try {config.load(input);} catch (IOException e) {throw new RuntimeException("An error occurred while reading classpath property '"+ redisPropertiesFilename+ "', see nested exceptions", e);} finally {try {input.close();} catch (IOException e) {// close quietly}}}RedisConfig jedisConfig = new RedisConfig();setConfigProperties(config, jedisConfig);return jedisConfig;}private void setConfigProperties(Properties properties,RedisConfig jedisConfig) {if (properties != null) {MetaObject metaCache = SystemMetaObject.forObject(jedisConfig);for (Map.Entry<Object, Object> entry : properties.entrySet()) {String name = (String) entry.getKey();String value = (String) entry.getValue();if (metaCache.hasSetter(name)) {Class<?> type = metaCache.getSetterType(name);if (String.class == type) {metaCache.setValue(name, value);} else if (int.class == type || Integer.class == type) {metaCache.setValue(name, Integer.valueOf(value));} else if (long.class == type || Long.class == type) {metaCache.setValue(name, Long.valueOf(value));} else if (short.class == type || Short.class == type) {metaCache.setValue(name, Short.valueOf(value));} else if (byte.class == type || Byte.class == type) {metaCache.setValue(name, Byte.valueOf(value));} else if (float.class == type || Float.class == type) {metaCache.setValue(name, Float.valueOf(value));} else if (boolean.class == type || Boolean.class == type) {metaCache.setValue(name, Boolean.valueOf(value));} else if (double.class == type || Double.class == type) {metaCache.setValue(name, Double.valueOf(value));} else {throw new CacheException("Unsupported property type: '"+ name + "' of type " + type);}}}}}}

在这里插入图片描述

小结
1. 二级缓存使用redis可以实现分布式缓存
2. 自定义实现二级缓存，通过实现Cache接口
3. RedisCache通过RedisConfigurationBuilder加载redis.properties中的配置
4. RedisCache使用了JedisPool
5. RedisCache使用了模板方法，完成putObject、getObject、removeObject、clear等操作

08.MyBatis插件

Mybatis插件原理

注册插件

//XMLConfigBuilder类的parseConfiguration方法 （解析SqlMapConfig.xml时）
private void parseConfiguration(XNode root) {try {// issue #117 read properties firstpropertiesElement(root.evalNode("properties"));Properties settings = settingsAsProperties(root.evalNode("settings"));loadCustomVfs(settings);loadCustomLogImpl(settings);typeAliasesElement(root.evalNode("typeAliases"));//解析插件  pluginElement(root.evalNode("plugins"));objectFactoryElement(root.evalNode("objectFactory"));objectWrapperFactoryElement(root.evalNode("objectWrapperFactory"));reflectorFactoryElement(root.evalNode("reflectorFactory"));settingsElement(settings);// read it after objectFactory and objectWrapperFactory issue #631environmentsElement(root.evalNode("environments"));databaseIdProviderElement(root.evalNode("databaseIdProvider"));typeHandlerElement(root.evalNode("typeHandlers"));mapperElement(root.evalNode("mappers"));} catch (Exception e) {throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e);}}

  private void pluginElement(XNode parent) throws Exception {if (parent != null) {for (XNode child : parent.getChildren()) {String interceptor = child.getStringAttribute("interceptor");Properties properties = child.getChildrenAsProperties();Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).getDeclaredConstructor().newInstance();interceptorInstance.setProperties(properties);//注册插件configuration.addInterceptor(interceptorInstance);}}}

  public void addInterceptor(Interceptor interceptor) {interceptorChain.addInterceptor(interceptor);}

public class InterceptorChain {//插件列表private final List<Interceptor> interceptors = new ArrayList<>();//应用插件public Object pluginAll(Object target) {for (Interceptor interceptor : interceptors) {target = interceptor.plugin(target);}return target;}//注册插件public void addInterceptor(Interceptor interceptor) {interceptors.add(interceptor);}public List<Interceptor> getInterceptors() {return Collections.unmodifiableList(interceptors);}}

通过Bean注入的方式注册拦截器的方式代码不在此处

应用插件

//Configuration类中public ParameterHandler newParameterHandler(MappedStatement mappedStatement, Object parameterObject, BoundSql boundSql) {ParameterHandler parameterHandler = mappedStatement.getLang().createParameterHandler(mappedStatement, parameterObject, boundSql);//应用插件，拦截ParameterHandlerparameterHandler = (ParameterHandler) interceptorChain.pluginAll(parameterHandler);return parameterHandler;}public ResultSetHandler newResultSetHandler(Executor executor, MappedStatement mappedStatement, RowBounds rowBounds, ParameterHandler parameterHandler,ResultHandler resultHandler, BoundSql boundSql) {ResultSetHandler resultSetHandler = new DefaultResultSetHandler(executor, mappedStatement, parameterHandler, resultHandler, boundSql, rowBounds);//应用插件，拦截ResultSetHandlerresultSetHandler = (ResultSetHandler) interceptorChain.pluginAll(resultSetHandler);return resultSetHandler;}public StatementHandler newStatementHandler(Executor executor, MappedStatement mappedStatement, Object parameterObject, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) {StatementHandler statementHandler = new RoutingStatementHandler(executor, mappedStatement, parameterObject, rowBounds, resultHandler, boundSql);//应用插件，拦截StatementHandlerstatementHandler = (StatementHandler) interceptorChain.pluginAll(statementHandler);return statementHandler;}public Executor newExecutor(Transaction transaction) {return newExecutor(transaction, defaultExecutorType);}public Executor newExecutor(Transaction transaction, ExecutorType executorType) {executorType = executorType == null ? defaultExecutorType : executorType;executorType = executorType == null ? ExecutorType.SIMPLE : executorType;Executor executor;if (ExecutorType.BATCH == executorType) {executor = new BatchExecutor(this, transaction);} else if (ExecutorType.REUSE == executorType) {executor = new ReuseExecutor(this, transaction);} else {executor = new SimpleExecutor(this, transaction);}if (cacheEnabled) {executor = new CachingExecutor(executor);}//应用插件，拦截Executorexecutor = (Executor) interceptorChain.pluginAll(executor);return executor;}

public class InterceptorChain {private final List<Interceptor> interceptors = new ArrayList<>();//应用拦截器，对目标对象进行拦截。target为ParameterHandler、ResultSetHandler、StatementHandler、Executorpublic Object pluginAll(Object target) {for (Interceptor interceptor : interceptors) {//链式拦截//遍历所有插件，对target进行拦截后，返回值为target，target将被下一个拦截器拦截target = interceptor.plugin(target);}return target;}
}

/*** @author Clinton Begin*/
public interface Interceptor {Object intercept(Invocation invocation) throws Throwable;//拦截器拦截default Object plugin(Object target) {//拦截器拦截return Plugin.wrap(target, this);}default void setProperties(Properties properties) {// NOP}}

生成插件拦截代理类

//Plugin类中  
public static Object wrap(Object target, Interceptor interceptor) {//1.构建签名映射表signatureMap。//记录拦截器所关注的方法签名及其对应的拦截逻辑Map<Class<?>, Set<Method>> signatureMap = getSignatureMap(interceptor);//2.确定目标对象接口Class<?> type = target.getClass();//找出所有需要被代理的接口Class<?>[] interfaces = getAllInterfaces(type, signatureMap);//3.创建代理对象if (interfaces.length > 0) {//该类，在signatureMap中有需要被拦截的方法才生成代理类return Proxy.newProxyInstance(type.getClassLoader(),interfaces,new Plugin(target, interceptor, signatureMap));}return target;}

构建签名映射表
- K:StatementHandler.class、Executor.class、ParameterHandler.class、ResultSetHandler.class
- V:update, query, flushStatements, commit, rollback…等

//Plugin类中  
private static Map<Class<?>, Set<Method>> getSignatureMap(Interceptor interceptor) {Intercepts interceptsAnnotation = interceptor.getClass().getAnnotation(Intercepts.class);if (interceptsAnnotation == null) {throw new PluginException("No @Intercepts annotation was found in interceptor " + interceptor.getClass().getName());}//1.提取@Intercepts注解中的签名数组Signature[] sigs = interceptsAnnotation.value();Map<Class<?>, Set<Method>> signatureMap = new HashMap<>();for (Signature sig : sigs) {Set<Method> methods = MapUtil.computeIfAbsent(signatureMap, sig.type(), k -> new HashSet<>());try {//2.获取拦截的类的方法。该方法是最终被拦截的方法Method method = sig.type().getMethod(sig.method(), sig.args());methods.add(method);} catch (NoSuchMethodException e) {throw new PluginException("Could not find method on " + sig.type() + " named " + sig.method() + ". Cause: " + e, e);}}return signatureMap;}

找出所有需要被代理的接口

//Plugin类中
private static Class<?>[] getAllInterfaces(Class<?> type, Map<Class<?>, Set<Method>> signatureMap) {Set<Class<?>> interfaces = new HashSet<>();while (type != null) {for (Class<?> c : type.getInterfaces()) {if (signatureMap.containsKey(c)) {interfaces.add(c);}}type = type.getSuperclass();}return interfaces.toArray(new Class<?>[0]);
}

执行拦截

//Plugin是一个InvocationHandler
public class Plugin implements InvocationHandler {private final Object target;private final Interceptor interceptor;private final Map<Class<?>, Set<Method>> signatureMap;private Plugin(Object target, Interceptor interceptor, Map<Class<?>, Set<Method>> signatureMap) {this.target = target;this.interceptor = interceptor;this.signatureMap = signatureMap;}//执行拦截@Overridepublic Object invoke(Object proxy, Method method, Object[] args) throws Throwable {try {Set<Method> methods = signatureMap.get(method.getDeclaringClass());//1.找到被拦截的方法if (methods != null && methods.contains(method)) {//2.执行拦截逻辑//interceptor.intercept方法由用户实现return interceptor.intercept(new Invocation(target, method, args));}return method.invoke(target, args);} catch (Exception e) {throw ExceptionUtil.unwrapThrowable(e);}}
}

小结

被拦截的类和方法

拦截的类	拦截的方法
Executor	update, query, flushStatements, commit, rollback,getTransaction, close, isClosed
ParameterHandler	getParameterObject, setParameters
StatementHandler	prepare, parameterize, batch, update, query
ResultSetHandler	handleResultSets, handleOutputParameters

代码执行链路
核心类图
- Interceptor：拦截器，定义了拦截逻辑，以及拦截器链的注册。
- InterceptorChain：拦截器链，将多个拦截器组成拦截器链。
- Plugin：Plugin 则是一种利用 Interceptor 实现的插件机制，它可以对指定的目标对象进行代理，并在方法调用前后插入额外的逻辑
- Invocation：封装了被拦截方法的信息，包括被拦截方法的对象，被拦截方法的方法，被拦截方法的参数。
- Plugin 是基于 Interceptor 实现的插件机制，而 Interceptor 是实现拦截器功能的接口。

自定义插件

MyBaits的Interceptor定义
```
public interface Interceptor {Object intercept(Invocation invocation) throws Throwable;default Object plugin(Object target) {return Plugin.wrap(target, this);}default void setProperties(Properties properties) {// NOP}}
```
- intercept方法：核心方法，最终会被调用，执行自定义的拦截逻辑。
- plugin方法：⽣成target的代理对象
- setProperties方法：传递插件所需参数，插件初始化的时候调⽤，也只调⽤⼀次

自定义Interceptor实现类

@Intercepts({//注意看这个⼤花括号，也就这说这⾥可以定义多个@Signature对多个地⽅拦截，都⽤这个拦截器@Signature(type = StatementHandler.class,//这是指拦截哪个接⼝method = "prepare",//这个接⼝内的哪个⽅法名，不要拼错了args = {Connection.class, Integer.class})// 这是拦截的⽅法的⼊参，按顺序写到这，不要多也不要少，如果⽅法重载，可是要通过⽅法名和⼊参来确定唯⼀的
})
public class MyPlugin implements Interceptor {/*拦截方法：只要被拦截的目标对象的目标方法被执行时，每次都会执行intercept方法*/@Overridepublic Object intercept(Invocation invocation) throws Throwable {System.out.println("对方法进行了增强....");return invocation.proceed(); //原方法执行}/*** 包装⽬标对象 为⽬标对象创建代理对象，会将当前Interceptor也包装进去** @param target 要拦截的对象* @return 代理对象*/@Overridepublic Object plugin(Object target) {Object wrap = Plugin.wrap(target, this);return wrap;}/*获取配置文件的参数插件初始化的时候调⽤，也只调⽤⼀次，插件配置的属性从这⾥设置进来*/@Overridepublic void setProperties(Properties properties) {System.out.println("获取到的配置文件的参数是：" + properties);}
}

sqlMapConfig.xml中配置插件，启用自定义的Interceptor实现类

    <plugins><plugin interceptor="com.muchfish.plugin.MyPlugin"><property name="name" value="tom"/></plugin></plugins>

测试

public class PluginTest {@Testpublic void test() throws IOException {InputStream resourceAsStream =Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession();IUserDao userMapper = sqlSession.getMapper(IUserDao.class);List<User> byPaging = userMapper.findAllUserAndRole();for (User user : byPaging) {System.out.println(user);}}
}

pageHelper分⻚插件

导⼊通⽤PageHelper的坐标

        <dependency><groupId>com.github.pagehelper</groupId><artifactId>pagehelper</artifactId><version>3.7.5</version></dependency><dependency><groupId>com.github.jsqlparser</groupId><artifactId>jsqlparser</artifactId><version>0.9.1</version></dependency>

在mybatis核⼼配置⽂件中配置PageHelper插件

    <plugins><!--   <plugin interceptor="com.muchfish.plugin.MyPlugin"><property name="name" value="tom"/></plugin>--><!--注意：分⻚助⼿的插件 配置在通⽤馆mapper之前*--><plugin interceptor="com.github.pagehelper.PageHelper"><property name="dialect" value="mysql"/></plugin></plugins>

测试分⻚数据获取

    @Testpublic void testPageHelper() throws IOException {InputStream resourceAsStream =Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactory sqlSessionFactory = newSqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession();IUserDao userMapper = sqlSession.getMapper(IUserDao.class);//设置分⻚参数PageHelper.startPage(1, 2);List<User> select = userMapper.findAllUserAndRole();for (User user : select) {System.out.println(user);}}

通⽤ mapper

基于插件实现单表增删改查?

导⼊通⽤tk.mybatis的坐标

<!--通用mapper-->
<dependency><groupId>tk.mybatis</groupId><artifactId>mapper</artifactId><version>3.1.2</version>
</dependency>

在mybatis核⼼配置⽂件中配置tk.mybatis插件

    <plugins><plugin interceptor="com.muchfish.plugin.MyPlugin"><property name="name" value="tom"/></plugin><!--注意：分⻚助⼿的插件 配置在通⽤馆mapper之前*--><plugin interceptor="com.github.pagehelper.PageHelper"><property name="dialect" value="mysql"/></plugin><plugin interceptor="tk.mybatis.mapper.mapperhelper.MapperInterceptor"><!--指定当前通用mapper接口使用的是哪一个--><property name="mappers" value="tk.mybatis.mapper.common.Mapper"/></plugin></plugins>

实体类设置主键

@Table(name = "user")
public class UserDO {@Id@GeneratedValue(strategy = GenerationType.IDENTITY)private Integer id;private String username;private String password;private String birthday;//...省略getter/setter
}

定义Dao继承Mapper类

import com.muchfish.pojo.UserDO;
import tk.mybatis.mapper.common.Mapper;public interface UserMapper extends Mapper<UserDO> {
}

测试

    @Testpublic void mapperTest() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml");SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream);SqlSession sqlSession = sqlSessionFactory.openSession();UserMapper mapper = sqlSession.getMapper(UserMapper.class);UserDO user = new UserDO();user.setId(1);UserDO user1 = mapper.selectOne(user);System.out.println(user1);//2.example方法Example example = new Example(User.class);example.createCriteria().andEqualTo("id",1);List<UserDO> users = mapper.selectByExample(example);for (UserDO user2 : users) {System.out.println(user2);}}

通用Mapper拦截器部分源码

/*** 通用Mapper拦截器** @author liuzh*/
@Intercepts({@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),@Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class})
})
public class MapperInterceptor implements Interceptor {private final MapperHelper mapperHelper = new MapperHelper();@Overridepublic Object intercept(Invocation invocation) throws Throwable {Object[] objects = invocation.getArgs();MappedStatement ms = (MappedStatement) objects[0];String msId = ms.getId();//不需要拦截的方法直接返回if (mapperHelper.isMapperMethod(msId)) {//第一次经过处理后，就不会是ProviderSqlSource了，一开始高并发时可能会执行多次，但不影响。以后就不会在执行了if (ms.getSqlSource() instanceof ProviderSqlSource) {mapperHelper.setSqlSource(ms);}}return invocation.proceed();}@Overridepublic Object plugin(Object target) {if (target instanceof Executor) {return Plugin.wrap(target, this);} else {return target;}}@Overridepublic void setProperties(Properties properties) {mapperHelper.setProperties(properties);}
}

  
// MapperHelper类中/*** 注册的通用Mapper接口*/private Map<Class<?>, MapperTemplate> registerMapper = new ConcurrentHashMap<Class<?>, MapperTemplate>();/*** 判断当前的接口方法是否需要进行拦截** @param msId* @return*/public boolean isMapperMethod(String msId) {if (msIdSkip.get(msId) != null) {return msIdSkip.get(msId);}for (Map.Entry<Class<?>, MapperTemplate> entry : registerMapper.entrySet()) {if (entry.getValue().supportMethod(msId)) {msIdSkip.put(msId, true);return true;}}msIdSkip.put(msId, false);return false;}

  // MapperHelper类中/*** 注册的通用Mapper接口*/private Map<Class<?>, MapperTemplate> registerMapper = new ConcurrentHashMap<Class<?>, MapperTemplate>();/*** 配置属性** @param properties*/
public void setProperties(Properties properties) {if (properties == null) {return;}String UUID = properties.getProperty("UUID");if (UUID != null && UUID.length() > 0) {setUUID(UUID);}//...省略//注册通用接口String mapper = properties.getProperty("mappers");if (mapper != null && mapper.length() > 0) {String[] mappers = mapper.split(",");for (String mapperClass : mappers) {if (mapperClass.length() > 0) {registerMapper(mapperClass);}}}
}/*** 注册通用Mapper接口** @param mapperClass* @throws Exception*/public void registerMapper(Class<?> mapperClass) {if (!registerMapper.containsKey(mapperClass)) {registerMapper.put(mapperClass, fromMapperClass(mapperClass));}//自动注册继承的接口Class<?>[] interfaces = mapperClass.getInterfaces();if (interfaces != null && interfaces.length > 0) {for (Class<?> anInterface : interfaces) {registerMapper(anInterface);}}}