Springboot自定义mybatis拦截器实现扩展

下面是详细讲解“Springboot自定义mybatis拦截器实现扩展”的完整攻略。

什么是Mybatis拦截器

Mybatis拦截器是一种拦截器模式的机制，通过动态代理技术拦截方法的调用，在方法执行前后进行拦截处理。拦截器可以拦截Mybatis数据库访问层的所有操作，如SQL解析、SQL执行、结果集处理等。通过Mybatis拦截器机制，我们可以在方法调用前、调用后、抛出异常时进行自定义扩展。

自定义Mybatis拦截器步骤

1. 创建Interceptor类

创建一个实现了Interceptor接口的类，该类需要实现三个方法：intercept()、plugin()和setProperties()。其中，intercept()方法是拦截器实际拦截操作的方法，plugin()方法用于生成代理对象，setProperties()方法用于传递配置参数。

public class MyInterceptor implements Interceptor {
   @Override
   public Object intercept(Invocation invocation) throws Throwable {
      // 拦截方法执行
      return invocation.proceed();
   }

   @Override
   public Object plugin(Object target) {
      // 生成代理对象
      return Plugin.wrap(target, this);
   }

   @Override
   public void setProperties(Properties properties) {
      // 传递配置参数
      String property1 = properties.getProperty("property1");
      String property2 = properties.getProperty("property2");
   }
}

1. 配置拦截器

在mybatis-config.xml配置文件中，配置拦截器。将自定义的拦截器添加到Mybatis的拦截器链中。

<configuration>
  <plugins>
    <plugin interceptor="com.example.MyInterceptor">
      <property name="property1" value="value1"/>
      <property name="property2" value="value2"/>
    </plugin>
  </plugins>
</configuration>

1. 使用拦截器

在需要使用拦截器的Mapper接口中，添加拦截器注解@Intercepts和@Signature。其中，@Intercepts是声明该类是一个拦截器，@Signature用于指定拦截的类和方法。

@Intercepts({
   @Signature(type = Executor.class, method = "update", args = {MappedStatement.class, Object.class})
})
public class MyInterceptor implements Interceptor {
   @Override
   public Object intercept(Invocation invocation) throws Throwable {
      // 拦截方法执行
      return invocation.proceed();
   }

   @Override
   public Object plugin(Object target) {
      // 生成代理对象
      return Plugin.wrap(target, this);
   }

   @Override
   public void setProperties(Properties properties) {
      // 传递配置参数
      String property1 = properties.getProperty("property1");
      String property2 = properties.getProperty("property2");
   }
}

示例1：拦截SQL语句

通过自定义Mybatis拦截器，我们可以拦截Mybatis SQL解析过程并进行自定义扩展。下面是一个拦截SQL语句并打印输出的示例：

@Intercepts({
   @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
public class SqlLogInterceptor implements Interceptor {
   @Override
   public Object intercept(Invocation invocation) throws Throwable {
      StatementHandler statementHandler = (StatementHandler) invocation.getTarget();
      BoundSql boundSql = statementHandler.getBoundSql();
      String sql = boundSql.getSql();
      System.out.println("执行SQL：" + sql);
      return invocation.proceed();
   }

   @Override
   public Object plugin(Object target) {
      return Plugin.wrap(target, this);
   }

   @Override
   public void setProperties(Properties properties) {
   }
}

示例2：限制查询结果数量

通过自定义Mybatis拦截器，我们也可以在查询前进行限制条件的判断，如果结果条数超过指定数量则不执行查询。下面是一个拦截SQL查询并限制结果数量的示例：

@Intercepts({
   @Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})
})
public class ResultLimitInterceptor implements Interceptor {
   private int limit = 10;

   public void setLimit(int limit) {
      this.limit = limit;
   }

   @Override
   public Object intercept(Invocation invocation) throws Throwable {
      MappedStatement mappedStatement = (MappedStatement) invocation.getArgs()[0];
      Object parameter = invocation.getArgs()[1];
      RowBounds rowBounds = (RowBounds) invocation.getArgs()[2];
      ResultHandler resultHandler = (ResultHandler) invocation.getArgs()[3];

      if (rowBounds == null || rowBounds == RowBounds.DEFAULT) {
         // 判断是否是查询操作
         if (mappedStatement.getSqlCommandType() == SqlCommandType.SELECT) {
            BoundSql boundSql = mappedStatement.getBoundSql(parameter);
            String sql = boundSql.getSql();
            // 判断SQL是否是查询全部
            if (sql.indexOf("count(*)") == -1 && sql.indexOf("COUNT(*)") == -1) {
               int count = getCount(invocation, mappedStatement, parameter, rowBounds, resultHandler);
               if (count > limit) {
                  throw new RuntimeException("查询结果过多，已超过限制。");
               }
            }
         }
      }
      return invocation.proceed();
   }

   private int getCount(Invocation invocation, MappedStatement mappedStatement, Object parameter, RowBounds rowBounds, ResultHandler resultHandler) throws SQLException {
      BoundSql countSql = new BoundSql(mappedStatement.getConfiguration(), "select count(*) from (" + mappedStatement.getBoundSql(parameter).getSql() + ") tmp_count", mappedStatement.getBoundSql(parameter).getParameterMappings(), parameter);

      Connection connection = (Connection) invocation.getArgs()[0];
      PreparedStatement countStmt = connection.prepareStatement(countSql.getSql());
      BoundSql countBoundSql = mappedStatement.getBoundSql(parameter);
      List<ParameterMapping> parameterMappings = countBoundSql.getParameterMappings();
      for (int i = 0; i < parameterMappings.size(); i++) {
         ParameterMapping parameterMapping = parameterMappings.get(i);
         Object value = countBoundSql.getAdditionalParameter(parameterMapping.getProperty());
         parameterMappings.get(i).getTypeHandler().setParameter(countStmt, i + 1, value, parameterMapping.getJdbcType());
      }
      ResultSet rs = countStmt.executeQuery();
      int count = 0;
      if (rs.next()) {
         count = rs.getInt(1);
      }
      rs.close();
      countStmt.close();
      return count;
   }

   @Override
   public Object plugin(Object target) {
      return Plugin.wrap(target, this);
   }

   @Override
   public void setProperties(Properties properties) {
   }
}

以上就是“Springboot自定义mybatis拦截器实现扩展”的完整攻略，包含了自定义Mybatis拦截器的步骤、示例1：拦截SQL语句、示例2：限制查询结果数量。希望对您有所帮助。