关于mybatis-plus:MybatisPlus-page-源码

IPage 外部原理也是基于拦截器，然而这个拦挡的是办法以及办法中的参数，这个也会判断是否是查问操作。如果是查问操作，才会进入分页的解决逻辑。进入分页逻辑解决后，拦截器会通过反射获取该办法的参数 进行判断是否存在 IPage 对象的实现类。如果不存在则不进行分页，存在则将该参数赋值给 IPage 对象。而后进行拼接 sql 的解决实现分页操作。然而应用 IPage 须要注入一个 bean 拦截器交给 spring 进行治理。如下。否则不会进行拦挡

1. 注入 paginationInterceptor 分页 bean

@Bean
public PaginationInterceptor paginationInterceptor() {
return new PaginationInterceptor();
}

1. 拦挡源码

public Object intercept(Invocation invocation) throws Throwable {StatementHandler statementHandler = PluginUtils.realTarget(invocation.getTarget());
     MetaObject metaObject = SystemMetaObject.forObject(statementHandler);
     // SQL 解析
     this.sqlParser(metaObject);
     // 先判断是不是 SELECT 操作  (2019-04-10 00:37:31 跳过存储过程)
     MappedStatement mappedStatement = (MappedStatement) metaObject.getValue("delegate.mappedStatement");
     if (SqlCommandType.SELECT != mappedStatement.getSqlCommandType()
            || StatementType.CALLABLE == mappedStatement.getStatementType()) {return invocation.proceed();
     }
        // 针对定义了 rowBounds，做为 mapper 接口办法的参数
     BoundSql boundSql = (BoundSql) metaObject.getValue("delegate.boundSql");
     Object paramObj = boundSql.getParameterObject();
     // 判断参数里是否有 page 对象
     IPage<?> page = null;
     if (paramObj instanceof IPage) {page = (IPage<?>) paramObj;
     } else if (paramObj instanceof Map) {for (Object arg : ((Map<?, ?>) paramObj).values()) {if (arg instanceof IPage) {page = (IPage<?>) arg;
     break; }
            }
        }
        /*
     * 不须要分页的场合，如果 size 小于 0 返回后果集 */ if (null == page || page.getSize() < 0) {return invocation.proceed();
     }
        if (this.limit > 0 && this.limit <= page.getSize()) {
            // 解决单页条数限度
     handlerLimit(page);
     }
        String originalSql = boundSql.getSql();
     Connection connection = (Connection) invocation.getArgs()[0];
     if (page.isSearchCount() && !page.isHitCount()) {SqlInfo sqlInfo = SqlParserUtils.getOptimizeCountSql(page.optimizeCountSql(), countSqlParser, originalSql);
     this.queryTotal(sqlInfo.getSql(), mappedStatement, boundSql, page, connection);
     if (page.getTotal() <= 0) {return null;}
        }
        DbType dbType = Optional.ofNullable(this.dbType).orElse(JdbcUtils.getDbType(connection.getMetaData().getURL()));
     IDialect dialect = Optional.ofNullable(this.dialect).orElse(DialectFactory.getDialect(dbType));
     String buildSql = concatOrderBy(originalSql, page);
    // 执行物理分页
    DialectModel model = dialect.buildPaginationSql(buildSql, page.offset(), page.getSize());
     Configuration configuration = mappedStatement.getConfiguration();
     List<ParameterMapping> mappings = new ArrayList<>(boundSql.getParameterMappings());
     Map<String, Object> additionalParameters = (Map<String, Object>) metaObject.getValue("delegate.boundSql.additionalParameters");
     model.consumers(mappings, configuration, additionalParameters);
     metaObject.setValue("delegate.boundSql.sql", model.getDialectSql());
     metaObject.setValue("delegate.boundSql.parameterMappings", mappings);
     return invocation.proceed();}

参考博客
`https://blog.csdn.net/xiaolegeaizy/article/details/108461284