数据库分页技术--hibernate篇

数据库分页技术在以后的开发中经常用到，以后主要是通过各种框架来实现的，他的主要原理是

long rows = 0; //数据总数

int size = 10; //每一页显示的记录条数

int page = 1; //当前第几页

int pageCount = 0; //一共有多少页

由这四个参数来完成。

下面是通过hibernate 来得到list，

mysql是由limit实现

不同的数据库方法不同，但使用了hibernate后，这些就都不用管了，他会自己实现功能

由下面这两个方法就行

//page代表当前页，如page=1,那么他将从第一天显示

query.setFirstResult((page-1)*10); //每条记录开始的位置

query.setMaxResults(size); //每页显示的记录条数

servlet.java

protected void doPost(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {

Configuration cfg=new Configuration().configure();
StandardServiceRegistryBuilder ssrb=new StandardServiceRegistryBuilder()
.applySettings(cfg.getProperties());
ServiceRegistry serviceRegistry=ssrb.build();

SessionFactory factory=cfg.buildSessionFactory(serviceRegistry);

Long rows=(long) 0;     //数据总数
int size=10;                //每一页显示的记录条数
int page=1;             //当前页数
int pageCount=0;        //页面总数

List list=new ArrayList();

String rp = req.getParameter("page");
if(rp!=null&&rp.length()>0){

try {
page = Integer.parseInt(rp);
} catch (NumberFormatException e) {
e.printStackTrace();
page = 1;
}
}
Session hsSession=null;
try {
hsSession=factory.openSession();
hsSession.beginTransaction();
//获取数据总数
rows =(Long) hsSession.createQuery("select count(*) from Bookbean bb").iterate().next();

Query query=hsSession.createQuery("from Bookbean bb");

query.setFirstResult((page-1)*10);      //每条记录开始的位置
query.setMaxResults(size);          //每页显示的记录条数

list=query.list();

hsSession.getTransaction().commit();

} catch (Exception e) {
e.printStackTrace();
hsSession.getTransaction().rollback();
}finally{
hsSession.close();
}

Iterator iterator=list.iterator();
while(iterator.hasNext()){
Bookbean bbBookbean=(Bookbean)iterator.next();
System.out.println(bbBookbean.getId()+" "+bbBookbean.getBname()+" "+bbBookbean.getPrice());

}

req.setAttribute("list", list);
req.setAttribute("pageCount", pageCount);
req.setAttribute("page", page);

req.getRequestDispatcher("/paging/book.jsp").forward(req, resp);

show.jsp

<form action="page" method="post">
<table>
<tr>
<td>序号</td>
<td>编号</td>
<td>书名</td>
<td>价格</td>
</tr>
<c:choose>
<c:when test="${empty list }">
<tr>
<td>对不起，没有查询到书本信息1</td>
</tr>
</c:when>

<c:otherwise>
<c:forEach items="${requestScope.list }" var="book" varStatus="id">
<tr>
<td>${id.index }</td>
<td>${book.id }</td>
<td>${book.bname }</td>
<td>${book.price }</td>
</tr>
</c:forEach>
<tr>
<td><a href="page?page=1">首页</a></td>
<td><a href="page?page=${page-1 }">上一页</a></td>
<td><a href="page?page=${page+1 }">下一页</a></td>

</tr>

</c:otherwise>
</c:choose>
<tr>
<td></td>
<td></td>
<td></td>
</tr>
</table>
</form>

—–华丽分割线—–

上面是我自己写的由hibernate实现

下面是老师的代码

servlet.java

public void doGet(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {

long rows = 0;      //数据总数
int size = 10;      //每一页显示的记录条数
int page = 1;       //当前第几页
int pageCount = 0;  //一共有多少页

String rp = request.getParameter("page");
if(rp!=null&&rp.length()>0){

try {
page = Integer.parseInt(rp);
} catch (NumberFormatException e) {
e.printStackTrace();
page = 1;
}

}

try {
InitialContext initCtx = new InitialContext();
Context ctx = (Context) initCtx.lookup("java:comp/env");
DataSource ds = (DataSource) ctx.lookup("jdbcmysql");

Connection conn = ds.getConnection();

PreparedStatement stat = conn.prepareStatement("select count(*) as rows from student");

ResultSet res = stat.executeQuery();

if(res.next()){
rows = res.getLong("rows");
}

//计算pageCount
if(rows%size==0){
pageCount = (int) (rows/size);
}else{
pageCount = (int) (rows/size)+1;
}

//根据当前页查询出需要的数据
List<Student> list = new ArrayList<Student>();

stat = conn.prepareStatement("select * from student limit ?,?");
stat.setInt(1, (page-1)*size);
stat.setInt(2, size);

res = stat.executeQuery();

while(res.next()){

Student s = new Student();
s.setId(res.getInt(1));
s.setName(res.getString(2));
s.setSex(res.getString(3));
s.setClazz(res.getString(4));

list.add(s);

}

conn.close();

//数据发送给JSP，并转发
request.setAttribute("list", list);
request.setAttribute("pageCount", pageCount);
request.setAttribute("page", page);

request.getRequestDispatcher("/stus.jsp").forward(request, response);

} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}

}

show.jsp

<h1> 学生信息</h1>
<table border="1" width="400" align="center">
<tr>
<th>序号</th>
<th>ID</th>
<th>姓名</th>
<th>性别</th>
<th>班级</th>
</tr>
<c:choose>
<c:when test="${empty list}">
<tr>
<td colspan="5" align="center">对不起！没有学生信息</td>
</tr>
</c:when>
<c:otherwise>
<c:forEach items="${list }" var="st" varStatus="index">
<tr>
<td>${index.count }</td>
<td>${st.id }</td>
<td>${st.name }</td>
<td>${st.sex }</td>
<td>${st.clazz }</td>
</tr>
</c:forEach>
<tr>
<td colspan="5">
<c:if test="${!(page==1) }">
<a href="stus?page=${page-1}">上一页</a> 
</c:if>
<c:if test="${!(page==pageCount) }">
<a href="stus?page=${page+1}">下一页</a> 
</c:if>
||<c:forEach var="p" begin="1" end="${pageCount}">
<a href="stus?page=${p}">第${p}页</a> 
</c:forEach>
||第${page }页
</td>
</tr>
</c:otherwise>
</c:choose>
</table>