從數據庫層面分頁(數據庫為MySQL，數據訪問層框架為MyBatis)

定義一個 PageBean 工具類。的工具類需要至少6個私有屬性，數據的totalRecord總數; totalPage 數據頁總數;pageSize：每頁幾個數據;pageNow 當前頁碼;列出當前頁碼的列表數據集合;startIndex sql 語句 查詢的起點。

package com . pagehelper . test ; 
import java . util . List ; 
public  class  PageBean < T >  { 
    /*total number of records*/
    private  int totalRecord ; 
    /*total number of pages*/
    private  int totalPage ; 
    /*data per page Number of
     items */private  int pageSize ; 
    /*Current page number*/
    private  int pageNow ; 
    /*Data collection obtained<T>Generic in order to make the tool class universal*/
    private List < T >list ; 
    /*Database query starts with that record*/
    private  int startIndex ; 
    public  PageBean ( int pageNow ,  int pageSize ,  int totalRecord ) { 
        this . totalRecord = totalRecord ; 
        /*Trinocular operation, totalRecord can be divisible by pageSize totalPage=totalRecord/pageSize
         * = Not divisible totalRecord TotalPage/* the pageSize +. 1/ 
        TotalPage = totalRecord % the pageSize == 0 ? TotalRecord / the pageSize : totalRecord / the pageSize + . 1 ; 
        the this . The pageSize = the pageSize ; 
        the this . PageNow = pageNow ; 
        startIndex =  ( pageNow - . 1 ) * pageSize ; 
    } 
    /*Constructor for fixed PageSize*/
    public  PageBean( int pageNow ,  int totalRecord ) { 
        this . totalRecord = totalRecord ; 
        pageSize =  5 ; 
        totalPage = totalRecord % pageSize == 0 ? totalRecord / pageSize : totalRecord / pageSize + 1 ; 
        this . pageNow = pageNow ; 
        startIndex =  ( pageNow - 1) * pageSize ; 
    } 
    /*Set,Get method*/
    public  int  getTotalRecord ( )  { 
        return totalRecord ; 
    }
    public  void  setTotalRecord ( int totalRecord )  { 
        this . totalRecord = totalRecord ; 
    }
    public  int  getTotalPage ( )  { 
        return totalPage ; 
    }
    public  void  setTotalPage ( int totalPage )  { 
        this . totalPage = totalPage ; 
    }
    public  int  getPageSize ( )  { 
        return pageSize ; 
    }
    public  void  setPageSize ( int pageSize )  { 
        this . pageSize = pageSize ; 
    }
    public  int  getPageNow ( )  { 
        return pageNow ; 
    }
    public  void  setPageNow ( int pageNow )  { 
        this . pageNow = pageNow ; 
    }
    public List < T >  getList ( )  { 
        return list ; 
    }
    public  void  setList ( List < T > list )  { 
        this . list = list ; 
    }
    public  int  getStartIndex ( )  { 
        return startIndex ; 
    }
    public  void  setStartIndex ( int startIndex )  { 
        this . startIndex = startIndex ; 
    }
}

Mapper 接口至少需要兩種方法，一種方法查詢總記錄數，另一種方法查詢數據。Worker 是我的數據庫的 pojo 類。

int  getTotalRecord ( ) ;
List < Worker >  selectAll ( @Param ( value =  "startIndex" )  int startIndex ,  @Param ( value =  "pageSize" ) int pageSize ) ;

以下代碼是Worker對應的resultMap和對應接口方法的實現

< mapper  namespace = " com.pagehelper.mapper.WorkerMapper "  > 
    < resultMap  id = " BaseResultMap "  type = " com.pagehelper.pojo.Worker "  > 
        < id  column = " wid "  property = " wid "  jdbcType = " INTEGER " /> 
        < result  column = " password " property = " password"  jdbcType = " VARCHAR " /> 
        < result  column = " company "  property = " company "  jdbcType = " VARCHAR " /> 
        < result  column = " department "  property = " department "  jdbcType = " VARCHAR " /> 
        < result  column = " job " property =" job "  jdbcType = " VARCHAR " /> 
        < result  column = " name "  property = " name "  jdbcType = " VARCHAR " /> 
        < result  column = " sex "  property = " sex "  jdbcType = " VARCHAR " /> 
        < result  column = "age "  property = " age "  jdbcType = " INTEGER " /> 
        < result  column = " tel "  property = " tel "  jdbcType = " VARCHAR " /> 
        < result  column = " email "  property = " email "  jdbcType = " VARCHAR " /> 
        < result  column = "regist_time " Property = " registTime "  the jdbcType = " TIMESTAMP " /> 
        < Result  column = " IMG "  Property = " IMG "  the jdbcType = " VARCHAR " /> 
    </ The resultMap > 
    < SELECT  ID = " getTotalRecord "  the resultType = " int " >
        SELECT COUNT(wid) FROM worker
    </ select > 
    < select  id = " selectAll "  resultMap = " BaseResultMap " >
        SELECT wid, password, company, department,job, name, sex, age, tel, email, regist_time,img FROM worker limit #{startIndex},#{pageSize}
    </ select > 
</ mapper >

服務層調用代碼：

@Override 
    public PageBean < the Worker >  the getAll ( int pageNow )  { 
        /* Get the total number of calls to method of recording getTotalRecord () */
        int totalRecord = workerMapper . GetTotalRecord ( ) ; 
        /* instantiate a class PageBean tool parameters passed pageNow, totalRecord, the PageSize fixed constructor I used here */ 
        PageBean < Worker > pageBean =  new  PageBean < > ( pageNow , totalRecord ) ;
        /* Call data query method selectAll (StartIndex, PageSize), parameters PageBean properties, the results of the query package to PageBean of the List */ 
        pageBean . SetList ( workerMapper . A selectAll ( pageBean . GetStartIndex ( ) , pageBean . GetPageSize ( ) ) ) ; 
        /*Return PageBean object*/
        return pageBean ; 
    }

因為構建的java項目沒有寫Controller和page，所以使用test方法顯示查詢結果

package com . pagehelper . test ;
import com . pagehelper . mapper . WorkerMapper ; 
import com . pagehelper . pojo . Worker ; 
import com . pagehelper . service . impl . WorkerServiceImpl ; 
import com . pagehelper . util . PageBean ; 
import org . apache . ibatis . io . Resources ; 
importorg . apache . ibatis . session . SqlSession ; 
import org . apache . ibatis . session . SqlSessionFactory ; 
import org . apache . ibatis . session . SqlSessionFactoryBuilder ;
import java . io . IOException ; 
import java . io . InputStream ;
public  class  Test1  {
    public  static  void  main ( String [ ] args )  throws IOException { 
        /*Get and load configuration file*/ 
        String resource =  "mybatis-config.xml" ; 
        InputStream inputStream = Resources . getResourceAsStream ( resource ) ; 
        /*Create a SqlSessionFactory session factory*/ 
        SqlSessionFactory sessionFactory =  new  SqlSessionFactoryBuilder ( ) . Build ( inputStream ) ; 
        /*Production SQLSession*/
        The SqlSession the session = the sessionFactory . The openSession ( ) ; 
        /* realized obtained WorkerMapper interface */ 
        WorkerMapper Mapper = the session . GetMapper ( WorkerMapper . Class ) ; 
        /* the Controller layer calls Service layer methods, examples of WorkerService */ 
        WorkerServiceImpl workerService =  new new  WorkerServiceImpl ( mapper ) ; 
        /*Call WorkerService method, return PageBean, encapsulate paging related data
        * Controller or after get data request is transmitted to the front end module to PageBean page, the page can obtain data directly via EL database, the current page number, total number of pages, and other related parameters */ 
        PageBean < the Worker > pageBean = workerService . The getAll ( . 1 ) ; 
        /* print the total number of records TotalRecord */ 
        the System . OUT . the println ( "total number of records:" + pageBean . getTotalRecord ( ) ) ( ) ) ; /* print from the database acquired data */for ( the worker worker : pageBean . getList ( ) ; 
        /* * print pages TotalPage/ 
        the System . OUT . the println ( "pages: " + pageBean . getTotalPage
        
         )  { 
            System . OUT . The println ( worker ) ; 
        } 
    } 
}

操作結果

log4j:ERROR Could not find value for key log4j.appender.LogFIle
log4j:ERROR Could not instantiate appender named "LogFIle".
2019-07-24 09:26:41 [main:1]-[DEBUG] ==> Preparing: SELECT COUNT(wid) FROM worker 
2019-07-24 09:26:41 [main:56]-[DEBUG] ==> Parameters: 
2019-07-24 09:26:41 [main:123]-[DEBUG] <== Total: 1
2019-07-24 09:26:41 [main:131]-[DEBUG] ==> Preparing: SELECT wid, password, company, department,job, name, sex, age, tel, email, regist_time,img FROM worker limit ?,? 
2019-07-24 09:26:41 [main:132]-[DEBUG] ==> Parameters: 0(Integer), 5(Integer)
2019-07-24 09:26:41 [main:148]-[DEBUG] <== Total: 5
Total records: 29
Total pages: 6
Worker{wid=100001, password='admin', company='Soft Emperor', department='Development Department', job='Super Admin', name='Super Admin', sex='Male', age= 18, tel='123', email='123@163.com', registTime=Sat Jul 20 11:33:18 CST 2019, img='default.jpg'}
Worker{wid=100002, password='123', company='Soft Emperor Group', department='Development Department', job='Employee', name='Administrator', sex='Male', age=122, tel='123', email='123@163.com', registTime=Sat Jul 20 16:00:59 CST 2019, img='default.jpg'}
Worker{wid=100003, password='admin', company='Soft Emperor', department='Development Department', job='Administrator', name='Administrator', sex='Male', age=18, tel='123', email='123@163.com', registTime=Sat Jul 20 11:33:20 CST 2019, img='default.jpg'}
Worker{wid=100004, password='123', company='Soft Emperor', department='Development Department', job='BOSS', name='123', sex='男', age=18, tel= '123', email='123', registTime=Sat Jul 20 15:10:33 CST 2019, img='default.jpg'}
Worker{wid=100005, password='123', company='Soft Emperor Group', department='Personnel Department', job='Manager', name='Sada', sex='Male', age=18, tel='123', email='123', registTime=Sat Jul 20 15:10:50 CST 2019, img='default.jpg'}
Process finished with exit code 0

Java開發工具還有很多，大家可要多多了解，在以后的學習中還會用到。