mybatisplus拦截器限制查询数量

可以使用Mybatis Plus提供的拦截器进行限制查询数量。具体实现步骤如下：

1. 自定义拦截器类实现Interceptor接口。

2. 在拦截器类中对需要进行限制查询数量的方法进行拦截，并添加限制查询数量的逻辑。

3. 在Mybatis Plus的配置文件中添加该拦截器。

下面是一个简单的示例代码：

public class LimitInterceptor implements Interceptor {

    private int limit;

    public LimitInterceptor(int limit) {
        this.limit = limit;
    }

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

        if (rowBounds != RowBounds.DEFAULT) {
            BoundSql boundSql = ms.getBoundSql(parameter);
            String sql = boundSql.getSql();
            sql = "SELECT * FROM (" + sql + ") LIMIT " + limit;
            BoundSql newBoundSql = new BoundSql(ms.getConfiguration(), sql, boundSql.getParameterMappings(), parameter);
            MappedStatement newMs = copyFromMappedStatement(ms, new BoundSqlSqlSource(newBoundSql));
            args[0] = newMs;
            args[2] = RowBounds.DEFAULT;
        }

        return invocation.proceed();
    }

    private MappedStatement copyFromMappedStatement(MappedStatement ms, SqlSource newSqlSource) {
        Builder builder = new Builder(ms.getConfiguration(), ms.getId(), newSqlSource, ms.getSqlCommandType());

        builder.resource(ms.getResource());
        builder.fetchSize(ms.getFetchSize());
        builder.statementType(ms.getStatementType());
        builder.keyGenerator(ms.getKeyGenerator());
        if (ms.getKeyProperties() != null && ms.getKeyProperties().length > 0) {
            builder.keyProperty(ms.getKeyProperties()[0]);
        }
        builder.timeout(ms.getTimeout());
        builder.parameterMap(ms.getParameterMap());
        builder.resultMaps(ms.getResultMaps());
        builder.cache(ms.getCache());
        builder.useCache(ms.isUseCache());

        return builder.build();
    }

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

    @Override
    public void setProperties(Properties properties) {
        this.limit = Integer.parseInt(properties.getProperty("limit", "100"));
    }

    private class BoundSqlSqlSource implements SqlSource {

        private BoundSql boundSql;

        public BoundSqlSqlSource(BoundSql boundSql) {
            this.boundSql = boundSql;
        }

        @Override
        public BoundSql getBoundSql(Object parameterObject) {
            return boundSql;
        }

    }

}

以上代码实现了一个拦截器，它会在执行带有RowBounds参数的查询语句时，将查询语句的结果集限制在指定数量（默认为100）以内。

在Mybatis Plus的配置文件中添加该拦截器：

<bean id="limitInterceptor" class="com.example.LimitInterceptor">
    <property name="limit" value="50" />
</bean>

<bean id="mybatisPlusInterceptor" class="com.baomidou.mybatisplus.extension.plugins.inner.InnerInterceptorChain">
    <property name="interceptors">
        <list>
            <ref bean="limitInterceptor" />
        </list>
    </property>
</bean>

这样，当执行带有RowBounds参数的查询语句时，查询结果集的数量就会被限制在50以内。