Jsp/Servlet复习笔记-----第8章 JSP表达式语言
8.1 表达式语言简介
JSP用于在网页上显示动态内容，通常需要在JSP页面中嵌入Java脚本以完成复杂功能。但是大量的Java脚本使得JSP页面难以维护。一种类似JavaScript语言—JSP表达式语言可用于在网页上生成动态内容，并代替JSP脚本元素。JSP表达式语言是从JSP2.0规范开始支持的技术。
8.2 禁用EL 表达式计算
8.3 变量
8.4 隐式对象
8.5 文字常量
8.6 运算符
8.7 保留字
8.8 表达式使用案例
8.9 本章小结
EL的主要功能：
精确的访问存储对象
Bean属性的简略记法
空值取代错误消息
之前代码：
<%
pageContext.setAttribute("name","darkness");
%>
<%
if(pageContext.getAttribute("name") != null)
{
%>
<%=pageContext.getAttribute("name")%>
<%
}
%>
<!--可以发现，这样，代码较多-->
<%
pageContext.setAttribute("name","darkness");
%>
${name}
使用表达式时不需要去判断属性是否为空
<!--如果在不同的属性范围中设置了同名的属性，则之后的同名属性无法找到-->
<!--按照四中标志位来寻找-->
<%
pageContext.setAttribute("name","darkness");
request.setAttribute("name","darkness");
%>
${name}
EL的主要功能在于MVC设计模式之中
后台：
package org.sky.darkness.servlet.el ;
import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class ELServletDemo01 extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
req.setAttribute("name","www.sky.org") ;
// 服务器端跳转
req.getRequestDispatcher("eldemo03.jsp").forward(req,resp) ;
}
public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
this.doGet(req,resp) ;
}
};
/*
<servlet>
<servlet-name>el01</servlet-name>
<servlet-class> org.sky.darkness.servlet.el.ELServletDemo01</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>el01</servlet-name>
<url-pattern>/eldemo/el_1</url-pattern>
</servlet-mapping>
*/
后台：${name}
*访问Bean的属性 ：
1、点号记法
${beanName.beanProperty}
2、数组记法
${beanName[“beanProperty”]}
package org.sky.darkness.servlet.el ;
import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class ELServletDemo02 extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
Simple s = new Simple() ;
s.setName("darkness") ;
req.setAttribute("sim",s) ;
// 服务器端跳转
req.getRequestDispatcher("eldemo04.jsp").forward(req,resp) ;
}
public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
this.doGet(req,resp) ;
}
};
/*
<servlet>
<servlet-name>el02</servlet-name>
<servlet-class> org.sky.darkness.servlet.el.ELServletDemo02</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>el02</servlet-name>
<url-pattern>/eldemo/el_2</url-pattern>
</servlet-mapping>
*/
package org.sky.darkness.servlet.el ;
public class Simple
{
private String name ;
public void setName(String name)
{
this.name = name ;
}
public String getName()
{
return this.name ;
}
};
如果保存的是一个对象，则在 JSP页面中要写以下代码：
<%@ page import=”org.sky.darkness.servlet.el.*”%>
<%
If(request.getAttribute(“sim”) != null){
Simple simp = (Simple)request.getAttribute(“sim”);
%>
<%=simp.getName()%>
<%
}
%>
<h1>${sim.name}</h1>
嵌套调用： ${ emp.name.firstName }
package org.sky.darkness.servlet.el ;
public class NameBean
{
private String firstName ;
private String lastName ;
public void setFirstName(String firstName)
{
this.firstName = firstName ;
}
public void setLastName(String lastName)
{
this.lastName = lastName ;
}
public String getFirstName()
{
return this.firstName ;
}
public String getLastName()
{
return this.lastName ;
}
};
package org.sky.darkness.servlet.el ;
public class EmployeeBean
{
private NameBean name ;
private CompanyBean company ;
public void setName(NameBean name)
{
this.name = name ;
}
public void setCompany(CompanyBean company)
{
this.company = company ;
}
public NameBean getName()
{
return this.name ;
}
public CompanyBean getCompany()
{
return this.company ;
}
};
package org.sky.darkness.servlet.el ;
public class CompanyBean
{
private String companyName ;
private String business ;
public void setCompanyName(String companyName)
{
this.companyName = companyName ;
}
public void setBusiness(String business)
{
this.business = business ;
}
public String getCompanyName()
{
return this.companyName ;
}
public String getBusiness()
{
return this.business ;
}
};
package org.sky.darkness.servlet.el ;
import java.io.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class ELServletDemo03 extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
NameBean nb = new NameBean() ;
nb.setFirstName("darkness") ;
nb.setLastName("depravedAngel") ;
CompanyBean cb = new CompanyBean() ;
cb.setCompanyName("www.sky.org") ;
cb.setBusiness("JAVA EE、JAVA SE、JAVA ME") ;
EmployeeBean eb = new EmployeeBean() ;
eb.setName(nb) ;
eb.setCompany(cb) ;
// 保存属性
req.setAttribute("emp",eb) ;
// 服务器端跳转
req.getRequestDispatcher("eldemo05.jsp").forward(req,resp) ;
}
public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
this.doGet(req,resp) ;
}
};
/*
<servlet>
<servlet-name>el03</servlet-name>
<servlet-class> org.sky.darkness.servlet.el.ELServletDemo03</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>el03</servlet-name>
<url-pattern>/eldemo/el_3</url-pattern>
</servlet-mapping>
*/
<h1>FirstName:${emp.name.firstName}</h1>
<h1>LastName:${emp.name.lastName}</h1>
<h1>CompanyName:${emp.company.companyName}</h1>
<h1>Business:${emp.company.business}</h1>
访问集合操作：
package org.sky.darkness.servlet.el ;
import java.io.* ;
import java.util.* ;
import javax.servlet.* ;
import javax.servlet.http.* ;
public class ELServletDemo04 extends HttpServlet
{
public void doGet(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
List l = new ArrayList() ;
Simple s = null ;
s = new Simple() ;
s.setName("darkness") ;
l.add(s) ;
s = new Simple() ;
s.setName("wind") ;
l.add(s) ;
s = new Simple() ;
s.setName("cloud") ;
l.add(s) ;
req.setAttribute("all",l) ;
// 服务器端跳转
req.getRequestDispatcher("eldemo06.jsp").forward(req,resp) ;
}
public void doPost(HttpServletRequest req,HttpServletResponse resp) throws IOException,ServletException
{
this.doGet(req,resp) ;
}
};
/*
<servlet>
<servlet-name>el02</servlet-name>
<servlet-class> org.sky.darkness.servlet.el.ELServletDemo02</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>el02</servlet-name>
<url-pattern>/eldemo/el_2</url-pattern>
</servlet-mapping>
*/
<%@page import="java.util.*"%>
<%--
要使用Iterator进行输出
--%>
<%
// List要使用Iterator输出
List l = (List)request.getAttribute("all") ;
Iterator iter = l.iterator() ;
while(iter.hasNext())
{
// 将取出的对象放在page范围之中
pageContext.setAttribute("sim",iter.next()) ;
%>
//调用隐式对象
<h1>${pageScope.sim.name}</h1>
<%
}
%>