24. Mybatis 分页插件-PageHelperPlus 源码

骑猪看日落 2024-04-17 15:00 64阅读 0赞

为提供Mybatis PageHelper 更优雅地调用方式, 笔者开发了Mybatis PageHelper Plus 插件.

## 1. 引入依赖 ##

笔者基于Mybatis 3.4.6 和 pageheler 5.1.10 开发的此插件

<properties>
        <mybatis.version>3.4.6</mybatis.version>
        <mybatis.pagehelper.version>5.1.10</mybatis.pagehelper.version>
    </properties>
    
    <dependencies>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>${mybatis.version}</version>
        </dependency>
        <dependency>
            <groupId>com.github.pagehelper</groupId>
            <artifactId>pagehelper</artifactId>
            <version>${mybatis.pagehelper.version}</version>
        </dependency>
    </dependencies>

## 2. 源码 ##

笔者一共新建了三个类

*  PageBounds: 用于设定分页的页码和每页大小
 *  PageResulst: 和PageInfo 完全等价, 用于自动封装分页信息和查询结果集.
 *  PageInterceptorPlus: 核心拦截器.

### 2.1 PageBounds ###

分页条件, 设置页码和每页条数.

public class PageBounds { 
    
        /** 页码 **/
        private int page;
    
        /** 每页大小 **/
        private int pageSize;
    
        public PageBounds() { 
        }
    
        public PageBounds(int page, int pageSize) { 
            this.page = page;
            this.pageSize = pageSize;
        }
    
        public static PageBounds of(int page, int pageSize) { 
            return new PageBounds(page, pageSize);
        }
        
        //setter, getter..
        
    }

### 2.2 PageInterceptorPlus ###

核心拦截器, 基础PageInterceptor

@Intercepts({ 
        @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 PageInterceptorPlus extends PageInterceptor { 
    
        @Override
        public Object intercept(Invocation invocation) throws Throwable { 
    
            // 默认不开启分页
            boolean pageAble = false;
    
            // 解析参数, 看是否包含PageBounds参数
            Object parameter = invocation.getArgs()[1];
            PageBounds pagerBounds = null;
    
            if( parameter instanceof MapperMethod.ParamMap){ 
                MapperMethod.ParamMap paramMap = (MapperMethod.ParamMap) parameter;
                Set<Map.Entry<String,Object>> set = paramMap.entrySet();
                for (Map.Entry<String, Object> entry : set)
                    if (entry.getValue() instanceof PageBounds) { 
                        pagerBounds = (PageBounds) entry.getValue();
                    }
            } else if (parameter instanceof PageBounds) { 
                pagerBounds = (PageBounds) parameter;
            }
    
            // 如果pageBounds 不为空, 则表示需要分页
            if (pagerBounds != null) { 
                PageHelper.startPage(pagerBounds.getPage(), pagerBounds.getPageSize());
                pageAble = true;
            }
    
            // 执行查询方法
            Object object = super.intercept(invocation);
    
            // 封装结果集
            if (pageAble) { 
                return new PageResult<>((List) object);
            }else { 
                return object;
            }
        }
    
        @Override
        public Object plugin(Object target) { 
            return Plugin.wrap(target, this);
        }
    
        @Override
        public void setProperties(Properties properties) { 
            super.setProperties(properties);
        }
    }

### 2.3 PageResult ###

*  笔者本想在拦截器中返回PageInfo 对象, 但是无奈PageInfo 并非是List 类型, 会报异常: Cause: java.lang.ClassCastException: com.github.pagehelper.PageInfo cannot be cast to java.util.List. 所以只能新创建一个PageResult 对象.
 *  此类由PageInfo 对象复制而来, 仅仅修改了total 参数的处理方式.

public class PageResult<T> extends ArrayList<T> { 
    
        private static final long serialVersionUID = 1412759446332294208L;
    
        //当前页
        private int pageNum;
        //每页的数量
        private int pageSize;
        //当前页的数量
        private int size;
    
        //由于startRow和endRow不常用，这里说个具体的用法
        //可以在页面中"显示startRow到endRow 共size条数据"
    
        //当前页面第一个元素在数据库中的行号
        private int startRow;
        //当前页面最后一个元素在数据库中的行号
        private int endRow;
        //总页数
        private int pages;
    
        //前一页
        private int prePage;
        //下一页
        private int nextPage;
    
        //是否为第一页
        private boolean isFirstPage = false;
        //是否为最后一页
        private boolean isLastPage = false;
        //是否有前一页
        private boolean hasPreviousPage = false;
        //是否有下一页
        private boolean hasNextPage = false;
        //导航页码数
        private int navigatePages;
        //所有导航页号
        private int[] navigatepageNums;
        //导航条上的第一页
        private int navigateFirstPage;
        //导航条上的最后一页
        private int navigateLastPage;
    
        private long total;
    
        public PageResult() { 
        }
    
        /** * 包装Page对象 * * @param list */
        public PageResult(List<T> list) { 
            this(list, 8);
        }
    
        /** * 包装Page对象 * * @param list page结果 * @param navigatePages 页码数量 */
        public PageResult(List<T> list, int navigatePages) { 
            super(list);
            if (list instanceof Page) { 
                Page page = (Page) list;
                this.pageNum = page.getPageNum();
                this.pageSize = page.getPageSize();
    
                this.pages = page.getPages();
                this.size = page.size();
                //由于结果是>startRow的，所以实际的需要+1
                if (this.size == 0) { 
                    this.startRow = 0;
                    this.endRow = 0;
                } else { 
                    this.startRow = page.getStartRow() + 1;
                    //计算实际的endRow（最后一页的时候特殊）
                    this.endRow = this.startRow - 1 + this.size;
                }
                total = page.getTotal();
            } else if (list instanceof Collection) { 
                this.pageNum = 1;
                this.pageSize = list.size();
    
                this.pages = this.pageSize > 0 ? 1 : 0;
                this.size = list.size();
                this.startRow = 0;
                this.endRow = list.size() > 0 ? list.size() - 1 : 0;
            }
            if (list instanceof Collection) { 
                this.navigatePages = navigatePages;
                //计算导航页
                calcNavigatepageNums();
                //计算前后页，第一页，最后一页
                calcPage();
                //判断页面边界
                judgePageBoudary();
            }
        }
    
        public static <T> PageInfo<T> of(List<T> list) { 
            return new PageInfo<T>(list);
        }
    
        public static <T> PageInfo<T> of(List<T> list, int navigatePages) { 
            return new PageInfo<T>(list, navigatePages);
        }
    
        /** * 计算导航页 */
        private void calcNavigatepageNums() { 
            //当总页数小于或等于导航页码数时
            if (pages <= navigatePages) { 
                navigatepageNums = new int[pages];
                for (int i = 0; i < pages; i++) { 
                    navigatepageNums[i] = i + 1;
                }
            } else {  //当总页数大于导航页码数时
                navigatepageNums = new int[navigatePages];
                int startNum = pageNum - navigatePages / 2;
                int endNum = pageNum + navigatePages / 2;
    
                if (startNum < 1) { 
                    startNum = 1;
                    //(最前navigatePages页
                    for (int i = 0; i < navigatePages; i++) { 
                        navigatepageNums[i] = startNum++;
                    }
                } else if (endNum > pages) { 
                    endNum = pages;
                    //最后navigatePages页
                    for (int i = navigatePages - 1; i >= 0; i--) { 
                        navigatepageNums[i] = endNum--;
                    }
                } else { 
                    //所有中间页
                    for (int i = 0; i < navigatePages; i++) { 
                        navigatepageNums[i] = startNum++;
                    }
                }
            }
        }
    
        /** * 计算前后页，第一页，最后一页 */
        private void calcPage() { 
            if (navigatepageNums != null && navigatepageNums.length > 0) { 
                navigateFirstPage = navigatepageNums[0];
                navigateLastPage = navigatepageNums[navigatepageNums.length - 1];
                if (pageNum > 1) { 
                    prePage = pageNum - 1;
                }
                if (pageNum < pages) { 
                    nextPage = pageNum + 1;
                }
            }
        }
    
        /** * 判定页面边界 */
        private void judgePageBoudary() { 
            isFirstPage = pageNum == 1;
            isLastPage = pageNum == pages || pages == 0;
            hasPreviousPage = pageNum > 1;
            hasNextPage = pageNum < pages;
        }
        //setter,gettter, toString 方法..
    }