第九章  Jsp标准标签库                               什么是Jsp标准标签库                               1)Jsp标准标签库(javaServer pages standard tag library)简称jstl是jsp已经为我们做好的                                 可以直接使用的用于编写和开发jsp页面的一组标准标签。                               2)jstl的最终目的是希望为我们提供一个无脚本环境,在此环境中用户可以使用标签来代替以前的Java程序段。                                 这样简化的jsp页面的开发，即使一个不懂java程序的用户也可以使用jstl来进行jsp页面的开发                               3)jstl包含三类标签：                                   A)核心标签库                                         11)通用标签                                        22)条件标签                                                      33)迭代标签                                   D)国际化与格式化标签库                                   E)Sql标签库                                                                    核心标签库                    1)核心标签库由通用标签、条件标签、迭代标签所构成                    2)通用标签用于操作jsp页面创建的范围变量                    3)条件标签用于对jsp页面中的代码进行条件判断和处理                    4)迭代标签用于循环遍历一个对像集合。相当于C#中的for earch                    5)要使用核心标签库，必须经过两个步骤                        A)设置工程需要库为JSTL1.1-->选择Project-->ProjectProperty-->RequiredLibrarles-->Add                        B)必须要导入核心标签库的Url格式如下：                                                  <%@  taglib  uri="http://java.sun.com/jsp/jstl/core"  prefix="c"%>                                     通用标签                   1)通用标签用于设置、删除和显示在jsp页面内创建的变量值。                   2)<c:set var="变量名" value="值" scope="范围"/>用于设置变量值                      其中的范围是:page,request,session.application,默认为page                      比如：                       <c:set var="uid" value="chen" scope="session"/>                      相当于:<% session.setAttribute("uid","chen"); %>                      只不过一个是jsp标签，一个是Javascriptlet Java代码段                   3)<c:out value="${变量名}"/>用于显示变量的值或直接通过EL来进行显示${变量名}                   4)<c:remove var="变量名" scope="范围"/>                                       条件标签                   1)条件标签以支持jsp页面中的各种条件,共有两种类型                      A)<c:if test="条件" >  相当于 if  (条件)                          内容                       {                        </c:if>                      }                                             举例：                        1)让用户输入两个数，求出最大值与最小值                          提示：创建一个页面max.jsp页面，然后提交到dowithmax.jsp页面                            <c:if test="${param.num1>0+param.num2}">                               <c:set var="max" value="${param.num1}"/>                               </c:if>                           <c:if test="${param.num1<0+param.num2}">                              <c:set var="max" value="${param.num2}"/>                           </c:if>                         最大值是:<c:out value="${max}"/>                                              2)让用户输入商品数量、商品单价、选择是否是会员来核算应付款                          一级会员:98折 二级会员:97折 三级会员:96折                          提示：创建一个buy.jsp页面,然后创建一个dowithbuy.jsp页面                            <c:if test="${param.vip==1}">                              <c:set var="discount" value="0.99"/>                           </c:if>                           <c:if test="${param.vip==2}">                              <c:set var="discount" value="0.98"/>                           </c:if>                          <c:if test="${param.vip==3}">                              <c:set var="discount" value="0.97"/>                          </c:if>                         应付款：${param.amount*param.unitprice*discount}                   　B)<c:choose>                           <c:when test="条件1">                                内容                           </c:when>                           <c:when test="条件2">                               内容                           </c:when>                                                                                       ..............                           <c:otherwise>                               内容                           </otherwise>                       </c:choose>                                  1:修改上页的两例                        2:让用户输入两个数和一个操作符，求出对应值                                                             迭代标签                   1)迭代标签相当于C#中的for earch，就是循环。                   2)迭代标签有两种形式。一种是<forEeach>，另外一种是<forTokens>                    A):<c:forEeach  var="迭代变量名" items="集合" varStatus="状态变量名">                        内容                      </c:forEeach>                        说明：                         var表示变量名相当于foreach(int item in 集合) 中的item                         items:相当于foreach中的item                         varStatus:是状态变量,可以省略                          　通常有：                            ${状态变量名.count}---从1开始的当前迭代项                            ${状态变量名.index}---从0开始的当前迭代项                        　                            举例：                            1)                             <%     String[] Car={"彩电","空调","手机","微波炉"};        %>                            所有的汔车如下：                                <c:forEach var="shop" items="<%=Car%>" varStatus="status">                                    <ul>第${status.count}种商品是${shop}</ul>                                </c:forEach>                           2)从数据库中查询出一个ResultSet并存放ArraryList。通过迭代标签进行输出                             public class shop                              {                                   public ArrayList getAllShop()                                      {                                                   ArrayList shops = new ArrayList();                                          ResultSet rs = tagapp.DbManager.RunHasResultSql("select * from shopinfo");                                          while (rs.next())                                           {                                               shop demo = new shop();                                               demo.setId(rs.getString(1));                                               demo.setName(rs.getString(2));                                               demo.setUnitPrice(rs.getInt(3));                                               shops.add(demo);                                            }                                      return shops;                                }                                     <jsp:useBean id="demo" scope="session" class="tagapp.shop"/>                                    <c:forEach var="item" items="<%=demo.getAllShop()%>">                                    ${item.id}　${item.name}　${item.unitPrice} <br>                                    </c:forEach>                            B):<c: forTokens items="以分隔符分开的字符串" delims="分隔符" var="迭代变量名">                                内容                              </c:forTokens                            应用举例：                            1)                              <c:set var="shops" value="彩电,空调,热水器"/>                              <c:forTokens delims="," items="${shops}" var="item">                               ${item}<br />                              </c:forTokens>                           2)从数据库中取出由固定分隔符分开的某个字段的值                             shop表：                                   s1-彩电-1200                                   s2-空调-1300       s3-微波炉-1500                                                                国际化与格式化标签                        1)国际化与格式化标签主要是用来实现一个WEB应用程序同时有几种国家的语言                        2)必须要导入:<%@ taglib uri="http://java.sun.com/jsp/jstl/fmt"  prefix="fmt" %>                        2)原理：                           A:为每一种语言做一个资源文件。比如：                               app_en.properties(英文), app_zh.properties(中文)                               格式形如：键=值                               app_en.properties文件的内容如下                                  uid=this my uid                                  pwd=this my pwd                                  login=login                                  reset=reset                               app_zh.properties文件的内容如下                                  uid=用户名                                  pwd=密码                                  login=登录                                  reset=重置                               1:注意资源文件命名的规范：文件名_两个字符标识. properties                               2:如果是中文为了避免乱码。要通过如下命令进行转换                                 native2ascii -encoding gb2312 源文件 目的文件                                   比如：                                  native2ascii -encoding gb2312 app_zh1.properties(源文件) app_zh1.properties(目的文件)                               3:资源文件一定要放在WEB-INF\classes下面,classes一定要手动创建******                             B:通过<fmt:setLocale value="en或zh"/>来决定使用那种语言的资源文件                             C:通过<fmt:setBundle basename="app"/>来决定要加载那些资源文件                             D:通过<fmt:message key="pwd" />来取出资源文件里面的值                             E:注意B,C的顺序不能颠倒                         举例:                             1)登录的中文与英文的例子                                       <c:if test="${param.language==null || param.language=='en'}">        <fmt:setLocale value="en"/>                                    </c:if>                                    <c:if test="${param.language=='zh'}">                                    <fmt:setLocale value="zh"/>                                    </c:if>                                    <fmt:setBundle basename="app"/>                                                                                    Sql标签库                            1)JSTL的SQL标签用于访问数据库，它提供的各种标签可用于在jsp页面内直接访问                              数据库，从而减少了JavaScriptlet代码                            2)要使用sql标签库，必须要导入<%@ taglib uri="http://java.sun.com/jsp/jstl/sql"  prefix="sql" %>                            3)Sql标签库由以下几种                               A:设置数据源                                 格式：<sql:setDataSource driver="sun.jdbc.odbc.JdbcOdbcDriver" url="jdbc:odbc:jsp" var="conn"/>                                  var:给数据源取一个别名，以后其它的sql标签将使用该变量做为数据源进行查询                                 scope:数据源变量的范围                               B:对数据库进行更新操作                                 格式：                                  <sql:update dataSource="${数据源变量}">                                   写上更新语句，是不返回结果的(delete,update,insert,create)                                  </sql:update>                                 dataSource:指定进行数据更新的连接                                  比如：                                                   <sql:update dataSource="${conn}">                                  update shopinfo set unitprice=unitprice+100                                 </sql:update>                                C:对数据库进行查询                                 格式：                                  <sql:query var="shops" dataSource="${conn}">                                       select语句                                  </sql:query>                                  var:给查询的结果取一个变量名                                   dataSource:指定进行数据更新的连接                                  此标签经常与<forEarch>标签一起使用，来显示查询出的值                                  在使用<forEarch>时可以使用begin end 来指定需要从那里开始到那里结束****                               比如：                                 <sql:query var="shops" dataSource="${conn}">                                   select * from shopinfo                                  </sql:query>                                <c:forEach var="row" items="${shops.rows}">                                                                   ${row.id}                                     ${row.name}                                      ${row.unitprice}                                </c:forEach>                               说明：                                1)<c:forEach var="row" items="${shops.rows}" begin="1"> 从第二行开始，全部取到                                2)<c:forEach var="row" items="${shops.rows}" begin="1" end="3"> 从第二行到第四行，全部取到                           D:为sql语句中的参数设置值，它一般是<sql:query>与<sql:update>的子标签                                格式：<sql:param   value="值"/>                                比如：                                 <c:set var="id" value="s1"/>                                 <sql:query var="shops" dataSource="${conn}">                                     select * from shopinfo where id=?                                     <sql:param value="${id}"/>                                 </sql:query>                                                                                           举例：                             1)通过标签从数据库查询出数据，并显示出来                             2)从表单填写商品信息并添加到数据库中                              3)让用户从表单中选择部门编号，从另一个页面中显示所有该部门的职工                                    2)在第一题的基础上进行数据的分页                                   <c:if test="${conn==null}">                                   <sql:setDataSource driver="sun.jdbc.odbc.JdbcOdbcDriver" url="jdbc:odbc:jsp" var="conn" scope="session"/>                                   <sql:query var="shops" dataSource="${conn}" scope="session">                                      elect * from test                                   </sql:query>                                    <c:set var="curpage" value="1" scope="session"/> //设置当前页的变量curpage                                  </c:if>                                     <c:choose>                                        c:when test="${shops.rowCount==0}">                                         没的查询的结果                                        </c:when>                                        <c:otherwise> //开始查询                                            <c:if test="${param.page == 'next'}"> //如果是下一页                                                <c:if test="${pagesize*curpage<shops.rowCount}"> //如果没有到末尾                                                   <c:set var="curpage" value="${curpage+1}" scope="session"/>                                                </c:if>                                            </c:if>                                       <c:if test="${param.page=='prio'}"> 如果是上页                                         <c:if test="${curpage>1}"> //如果没有到首页                                            <c:set var="curpage" value="${curpage-1}" scope="session"/>                                         </c:if>                                        </c:if>                                       <c:forEach var="row" items="${shops.rows}" begin="${pagesize*(curpage-1)}" end="${pagesize*curpage-1}" >                                          <tr>                                              <td><div align="center">${row.id}</div></td>                                              <td><div align="center">${row.a}</div></td>                                              <td><div align="center">${row.b}</div></td>                                           </tr>                                        </c:forEach>                                          <a href="jsp1.jsp?page=next">下一页</a>　<a href="jsp1.jsp?page=prio">上一页</a>                                       </c:otherwise>                                      </c:choose>

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