Mybatis-Plus入门系列(1)- MybatisPlus插件简介

ゝ一世哀愁。 2023-10-10 12:34 48阅读 0赞

### Mybatis插件 ###

Mybatis插件，实际上就是一个拦截器，应用代理模式，在方法级别上进行拦截。可以实现分页、SQL打印监控、公共字段赋值等功能，基本上可以控制SQL执行的各个阶段，如执行阶段，参数处理阶段，语法构建阶段，结果集处理阶段，具体可以根据项目业务来实现对应业务逻辑。

public interface Interceptor {
        
    	// 可从Invocation参数中拿到执行方法的对象，方法，方法参数，从而实现各种业务逻辑
      Object intercept(Invocation invocation) throws Throwable;
    	// 生成代理对象
      default Object plugin(Object target) {
        
        return Plugin.wrap(target, this);
      }
      // 设置一些属性变量
      default void setProperties(Properties properties) {
        
        // NOP
      }
    }

### MybatisPlus插件 ###

plus提供了InnerInterceptor来实现插件功能，已经提供了很多插件使用，我们可以通过添加直接使用，也可以自己实现InnerInterceptor，然后通过MybatisPlusInterceptor添加插件来使用。  
目前已有的功能:

*  自动分页: PaginationInnerInterceptor
 *  多租户: TenantLineInnerInterceptor
 *  动态表名: DynamicTableNameInnerInterceptor
 *  乐观锁: OptimisticLockerInnerInterceptor
 *  sql性能规范: IllegalSQLInnerInterceptor
 *  防止全表更新与删除: BlockAttackInnerInterceptor
 *  数据权限：DataPermissionInterceptor

@SuppressWarnings({
 "rawtypes"})
 public interface InnerInterceptor {
 
 
 /**
 * 判断是否执行 {@link Executor#query(MappedStatement, Object, RowBounds, ResultHandler, CacheKey, BoundSql)}
 * 
 * 如果不执行query操作,则返回 {@link Collections#emptyList()}
 *
 * @param executor Executor(可能是代理对象)
 * @param ms MappedStatement
 * @param parameter parameter
 * @param rowBounds rowBounds
 * @param resultHandler resultHandler
 * @param boundSql boundSql
 * @return 新的 boundSql
 */
 default boolean willDoQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
 
 return true;
 }
 
 /**
 * {@link Executor#query(MappedStatement, Object, RowBounds, ResultHandler, CacheKey, BoundSql)} 操作前置处理
 * 
 * 改改sql啥的
 *
 * @param executor Executor(可能是代理对象)
 * @param ms MappedStatement
 * @param parameter parameter
 * @param rowBounds rowBounds
 * @param resultHandler resultHandler
 * @param boundSql boundSql
 */
 default void beforeQuery(Executor executor, MappedStatement ms, Object parameter, RowBounds rowBounds, ResultHandler resultHandler, BoundSql boundSql) throws SQLException {
 
 // do nothing
 }
 
 /**
 * 判断是否执行 {@link Executor#update(MappedStatement, Object)}
 * 
 * 如果不执行update操作,则影响行数的值为 -1
 *
 * @param executor Executor(可能是代理对象)
 * @param ms MappedStatement
 * @param parameter parameter
 */
 default boolean willDoUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
 
 return true;
 }
 
 /**
 * {@link Executor#update(MappedStatement, Object)} 操作前置处理
 * 
 * 改改sql啥的
 *
 * @param executor Executor(可能是代理对象)
 * @param ms MappedStatement
 * @param parameter parameter
 */
 default void beforeUpdate(Executor executor, MappedStatement ms, Object parameter) throws SQLException {
 
 // do nothing
 }
 
 /**
 * {@link StatementHandler#prepare(Connection, Integer)} 操作前置处理
 * 
 * 改改sql啥的
 *
 * @param sh StatementHandler(可能是代理对象)
 * @param connection Connection
 * @param transactionTimeout transactionTimeout
 */
 default void beforePrepare(StatementHandler sh, Connection connection, Integer transactionTimeout) {
 
 // do nothing
 }
 
 default void setProperties(Properties properties) {
 
 // do nothing
 }
 }

@Intercepts(
 {
 
 @Signature(type = StatementHandler.class, method = "prepare", args = {
 Connection.class, Integer.class}),
 @Signature(type = Executor.class, method = "update", args = {
 MappedStatement.class, Object.class}),
 @Signature(type = Executor.class, method = "query", args = {
 MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}),
 @Signature(type = Executor.class, method = "query", args = {
 MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class, CacheKey.class, BoundSql.class}),
 }
 )
 public class MybatisPlusInterceptor implements Interceptor {
 
 
 @Setter
 private List<InnerInterceptor> interceptors = new ArrayList<>();
 
 @Override
 public Object intercept(Invocation invocation) throws Throwable {
 
 Object target = invocation.getTarget();
 Object[] args = invocation.getArgs();
 if (target instanceof Executor) {
 
 final Executor executor = (Executor) target;
 Object parameter = args[1];
 boolean isUpdate = args.length == 2;
 MappedStatement ms = (MappedStatement) args[0];
 if (!isUpdate && ms.getSqlCommandType() == SqlCommandType.SELECT) {
 
 RowBounds rowBounds = (RowBounds) args[2];
 ResultHandler resultHandler = (ResultHandler) args[3];
 BoundSql boundSql;
 if (args.length == 4) {
 
 boundSql = ms.getBoundSql(parameter);
 } else {
 
 // 几乎不可能走进这里面,除非使用Executor的代理对象调用query[args[6]]
 boundSql = (BoundSql) args[5];
 }
 for (InnerInterceptor query : interceptors) {
 
 if (!query.willDoQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql)) {
 
 return Collections.emptyList();
 }
 query.beforeQuery(executor, ms, parameter, rowBounds, resultHandler, boundSql);
 }
 CacheKey cacheKey = executor.createCacheKey(ms, parameter, rowBounds, boundSql);
 return executor.query(ms, parameter, rowBounds, resultHandler, cacheKey, boundSql);
 } else if (isUpdate) {
 
 for (InnerInterceptor update : interceptors) {
 
 if (!update.willDoUpdate(executor, ms, parameter)) {
 
 return -1;
 }
 update.beforeUpdate(executor, ms, parameter);
 }
 }
 } else {
 
 // StatementHandler
 final StatementHandler sh = (StatementHandler) target;
 Connection connections = (Connection) args[0];
 Integer transactionTimeout = (Integer) args[1];
 for (InnerInterceptor innerInterceptor : interceptors) {
 
 innerInterceptor.beforePrepare(sh, connections, transactionTimeout);
 }
 }
 return invocation.proceed();
 }
 
 @Override
 public Object plugin(Object target) {
 
 if (target instanceof Executor || target instanceof StatementHandler) {
 
 return Plugin.wrap(target, this);
 }
 return target;
 }
 
 public void addInnerInterceptor(InnerInterceptor innerInterceptor) {
 
 this.interceptors.add(innerInterceptor);
 }
 
 public List<InnerInterceptor> getInterceptors() {
 
 return Collections.unmodifiableList(interceptors);
 }
 
 /**
 * 使用内部规则,拿分页插件举个栗子:
 * 
 * - key: "@page" ,value: "com.baomidou.mybatisplus.extension.plugins.inner.PaginationInnerInterceptor"
 * - key: "page:limit" ,value: "100"
 * 
 * 解读1: key 以 "@" 开头定义了这是一个需要组装的 `InnerInterceptor`, 以 "page" 结尾表示别名
 * value 是 `InnerInterceptor` 的具体的 class 全名
 * 解读2: key 以上面定义的 "别名 + ':'" 开头指这个 `value` 是定义的该 `InnerInterceptor` 属性需要设置的值
 * 
 * 如果这个 `InnerInterceptor` 不需要配置属性也要加别名
 */
 @Override
 public void setProperties(Properties properties) {
 
 PropertyMapper pm = PropertyMapper.newInstance(properties);
 Map<String, Properties> group = pm.group("@");
 group.forEach((k, v) -> {
 
 InnerInterceptor innerInterceptor = ClassUtils.newInstance(k);
 innerInterceptor.setProperties(v);
 addInnerInterceptor(innerInterceptor);
 });
 }
 }