MyBatis Plugins

MyBatis 允许在已映射语句执行过程中的某一点进行拦截调用。默认情况下，MyBatis 允许使用插件来拦截的方法调用包括：

Executor (update, query, flushStatements, commit, rollback, getTransaction, close, isClosed)
ParameterHandler (getParameterObject, setParameters)
ResultSetHandler (handleResultSets, handleOutputParameters)
StatementHandler (prepare, parameterize, batch, update, query)

除了用插件来修改 MyBatis 核心行为之外，还可以通过完全覆盖配置类来达到目的。只需继承后覆盖其中的每个方法，再把它传递到 SqlSessionFactoryBuilder.build(myConfig) 方法即可。

一、可拦截的接口

1.Executor-执行器

public interface Executor {
    // 不需要 ResultHandler
    ResultHandler NO_RESULT_HANDLER = null;
    // 更新
    int update(MappedStatement ms, Object parameter) throws SQLException;
    // 查询(先查缓存)，带分页，BoundSql
    <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, CacheKey cacheKey, BoundSql boundSql) throws SQLException;
    // 查询，带分页
    <E> List<E> query(MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException;
    // 查询游标
    <E> Cursor<E> queryCursor(MappedStatement ms, Object parameter, RowBounds rowBounds) throws SQLException;
    // 刷新(Statement)批处理语句
    List<BatchResult> flushStatements() throws SQLException;
    // 提交事务，参数为是否要强制
    void commit(boolean required) throws SQLException;
    // 回滚事务，参数为是否要强制
    void rollback(boolean required) throws SQLException;
    // 创建 CacheKey
    CacheKey createCacheKey(MappedStatement ms, Object parameterObject, RowBounds rowBounds, BoundSql boundSql);
    // 判断是否缓存了，通过 CacheKey
    boolean isCached(MappedStatement ms, CacheKey key);
    // 清理 Session(本地一级) 缓存
    void clearLocalCache();
    // 延迟加载
    void deferLoad(MappedStatement ms, MetaObject resultObject, String property, CacheKey key, Class<?> targetType);
    // 获取事务
    Transaction getTransaction();
    // 关闭连接
    void close(boolean forceRollback);
    // 是否关闭
    boolean isClosed();
    // 设置 Executor
    void setExecutorWrapper(Executor executor);
}

2.ParameterHandler-参数处理器

public interface ParameterHandler {
    // 获取参数
    Object getParameterObject();
    // 设置参数
    void setParameters(PreparedStatement ps) throws SQLException;
}

3.ResultSetHandler-结果集处理器

public interface ResultSetHandler {
    // 将结果集转化成 List
    <E> List<E> handleResultSets(Statement stmt) throws SQLException;
    // 将结果集转化成 Cursor
    <E> Cursor<E> handleCursorResultSets(Statement stmt) throws SQLException;
    // 处理存储过程的 OUT(输出) 参数
    void handleOutputParameters(CallableStatement cs) throws SQLException;
}

4.StatementHandler-SQL语句处理器

public interface StatementHandler {
    // 准备语句
    Statement prepare(Connection connection, Integer transactionTimeout) throws SQLException;
    // 参数处理
    void parameterize(Statement statement) throws SQLException;
    // 批量处理
    void batch(Statement statement) throws SQLException;
    // 更新处理
    int update(Statement statement) throws SQLException;
    // 查询处理，结果给 ResultHandler
    <E> List<E> query(Statement statement, ResultHandler resultHandler) throws SQLException;
    <E> Cursor<E> queryCursor(Statement statement) throws SQLException;
    // 获取绑定 SQL 语句
    BoundSql getBoundSql();
    // 获取参数处理器
    ParameterHandler getParameterHandler();
}

二、自定义插件

实现 Interceptor 接口，并指定想要拦截的方法签名。最后在 xml 文件中配置全类名即可。

1.bean

@Alias("myUser")
public class MyUser implements Serializable {
    private Integer id;
    private String name;
    private Integer age;

2.dao接口

public interface MyUserMapperAnnotation {
    @Select("select * from myuser")
    List<MyUser> selectMyUser(String a);
}

3.mybatis-config.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>
    <!-- 注意 plugins 在配置文件中的位置
        properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, plugins?, environments?, databaseIdProvider?, mappers? -->
    <plugins>
        <plugin interceptor="com.plugins.ExamplePlugin">
            <property name="someProperty" value="100"/>
        </plugin>
    </plugins>

    <environments default="development-mysql">
        <environment id="development-mysql">
            <transactionManager type="JDBC"/>
            <dataSource type="POOLED">
                <property name="driver" value="com.mysql.cj.jdbc.Driver"/>
                <property name="url" value="jdbc:mysql://192.168.8.136:3306/mybatis?allowMultiQueries=true"/>
                <property name="username" value="root"/>
                <property name="password" value="root"/>
            </dataSource>
        </environment>
    </environments>

    <mappers>
        <mapper class="com.dao.MyUserMapperAnnotation"/>
    </mappers>
</configuration>

4.ExamplePlugin

/**
 * @Intercepts 拦截器注解，包括一个或多个 @Signature
 * @Signature 拦截的目标类信息，包括 type、method、args
 * * type 要拦截的接口类型
 * * method 接口中的方法名
 * * args 方法的所有入参类型
 */
@Intercepts({
        @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class ExamplePlugin implements Interceptor {
    /**
     * 拦截目标对象的目标方法的执行，将自定义逻辑写在该方法中
     */
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        System.out.println("ExamplePlugin...intercept:" + invocation.getMethod());

        // MetaObject 是 Mybatis 提供的一个用于访问对象属性的对象
        MetaObject metaObject = SystemMetaObject.forObject(invocation);

        System.out.println("当前拦截到的对象：" + metaObject.getValue("target"));
        System.out.println("SQL语句：" + metaObject.getValue("target.delegate.boundSql.sql"));
        System.out.println("SQL语句入参：" + metaObject.getValue("target.delegate.parameterHandler.parameterObject"));
        System.out.println("SQL语句类型：" + metaObject.getValue("target.delegate.parameterHandler.mappedStatement.sqlCommandType"));
        System.out.println("Mapper方法全路径名：" + metaObject.getValue("target.delegate.parameterHandler.mappedStatement.id"));

        // 修改 SQL 语句
        String newSQL = metaObject.getValue("target.delegate.boundSql.sql") + " limit 2";
        metaObject.setValue("target.delegate.boundSql.sql", newSQL);
        System.out.println("修改后SQL语句：" + newSQL);

        // 返回执行结果
        return invocation.proceed();
    }

    /**
     * 为目标对象创建一个代理对象，使用 Plugin.wrap(target,this) 即可
     * @param target 上次包装的代理对象
     * @return 本次包装过的代理对象
     */
    @Override
    public Object plugin(Object target) {
        System.out.println("ExamplePlugin...plugin:" + target);
        return Plugin.wrap(target, this);
    }

    /**
     * 获取自定义配置参数
     * @param properties
     */
    @Override
    public void setProperties(Properties properties) {
        System.out.println("插件配置信息：" + properties);
        System.out.println("someProperty：" + properties.get("someProperty"));
    }
}

5.Main

public static void main(String[] args) throws IOException {
    SqlSession session = null;
    try {
        InputStream inputStream = Resources.getResourceAsStream("mybatis-config.xml");
        SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);

        session = sqlSessionFactory.openSession();
        MyUserMapperAnnotation mapper = session.getMapper(MyUserMapperAnnotation.class);

        System.out.println(mapper.selectMyUser("asdsad"));
    } finally {
        if (session != null) {
            session.close();
        }
    }
}

http://www.mybatis.org/mybatis-3/zh_CN/configuration.html#plugins

posted @ 2019-04-02 20:03 江湖小小白阅读(4747) 评论(0) 编辑收藏举报

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