RequestDispatcher简介
public interface RequestDispatcher {public void forward(ServletRequest request, ServletResponse response)throws ServletException, IOException;public void include(ServletRequest request, ServletResponse response)throws ServletException, IOException; }
RequestDispatcher.forward(request, response)
public class User{private String name;private int age;public String getName(){return name ;}public void setName( String name ){this .name = name ;}public int getAge() {return age ;}public void setAge( int age ){this .age = age ;} }
UsersServlet.java
public class UsersServlet extends HttpServlet {private static final long serialVersionUID = 1L ;protected void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException , IOException {/*****************一般实际开发这些用户数据都是从数据库查出来的*********/List <User > users = new ArrayList <> ();User u1 = new User () ;u1 .setAge ( 20) ;u1 .setName ( "Bob") ;User u2 = new User () ;u2 .setAge ( 21) ;u2 .setName ( "Tony") ;users .add ( u1) ;users .add ( u2) ;/*********************************************/request .setAttribute ( "users", users) ; //对request 进制预处理准备工作request .getRequestDispatcher ( "users.jsp").forward( request , response );//转发到users.jsp,让他去具体响应
}
}
<%@ page contentType= "text/html; charset=UTF-8" pageEncoding ="UTF-8" trimDirectiveWhitespaces= "true"session ="true" %> <%@ taglib prefix= "c" uri = "http://java.sun.com/jsp/jstl/core" %><!DOCTYPE html> < html> <head> <meta http-equiv = "Content-Type" content ="text/html; charset=UTF-8"> <title> 用户列表</title> </head> <body><p> -----------------转发到的资源users.jsp产生的响应数据------------------ </p>< c:forEach var ="user" items= " ${users}" > 用户姓名:${user.name} 用户年龄:${user.age} <br /> </ c:forEach> </body> </html>
快速排序 Java,
Java原理。例子2:不使用Attribute,使用Paramter向转发的资源传递参数。
虽然request对象没有setParameter方法来设置参数,但是我们可以在转发的URL后通过QueryString 的方式添加。JSP中的<jsp:foward>标签下的<jsp:param>标签就是使用的这个原理。
java 线程池底层原理?
AimServlet.java
public class AimServlet extends HttpServlet {private static final long serialVersionUID = 1L ;protected void doGet( HttpServletRequest request , HttpServletResponse response) throws ServletException , IOException {request .getRequestDispatcher ( "foo.jsp?num=1") . forward( request , response );} }
foo.jsp
<%@ page contentType= "text/html; charset=UTF-8" pageEncoding ="UTF-8" trimDirectiveWhitespaces= "true"session ="true" %> <%@ taglib prefix= "c" uri = "http://java.sun.com/jsp/jstl/core" %><! DOCTYPE html> <html> <head> <meta http-equiv = "Content-Type" content ="text/html; charset=UTF-8"> <title> 标题</title> </head> <body>通过forward传递过来的参num=${param.num}</body> </html>
java注解工作原理,
eclipse查看一个接口有哪些实现类,
RequestDispatcher.include(request, response)
注意事项:
JavaWeb项目,1、被包含者不能设置ServletResponse的响应状态和响应头(否则并不会产生效果),因为这些都是包含者做的事,被包含者只需要产生响应数据解可以了。
2、不同于 forward中的request的传递特性:在被包含的资源中从request中获取请求路径相关的信息,发现依然是原始请求的路径,也就是浏览器地址栏相关的路径,也就是说被包含的资源获得的request对象的路径属性和原始请求资源的路径一样(见下面的例子1)。其它的API调用也是一样的(Attribute 和Parameter)。
JavaBeans?例子1
TargetServlet.java
public class TargetServlet extends HttpServlet {private static final long serialVersionUID = 1L ;protected void doGet( HttpServletRequest request , HttpServletResponse response) throws ServletException , IOException {response .setContentType ( "text/html;charset=utf-8" );PrintWriter out = response .getWriter () ;out .println ( "----------来自TargetServlet的告白----------------<br />" ) ;out .print ( "我偷懒了,下面的响应数据并不是我自己产生的,而是包含的其它资源产生的<br/>" ) ;request .getRequestDispatcher ( "test.jsp") . include( request , response );out .flush () ;out .close () ;} }
test.jsp
<%@ page contentType= "text/html; charset=UTF-8" pageEncoding = "UTF-8" trimDirectiveWhitespaces = "true"session = "false" %><p> ------------------------来自test.jsp的告白-------------------------- </p> <p> 我输出的响应数据将被其它的资源包含 </p> 请的URL是 <%= request.getRequestURL().toString() %> ,可以看出客户端真正请求的不是我,我只是幕后工作者。 <p> 但我很开心,因为响应给客户端的数据一部分来自于我 </p>
Java注解原理,
例子2:通过包含路径后追加QueryString来向被包含资源传递参数,以及通过request.setAttribute传递属性。
同样, JSP中的<jsp:include>标签下的<jsp:param>标签就是通过在含路径后追加QueryString达到的传递参数的效果。
public class TargetServlet extends HttpServlet {private static final long serialVersionUID = 1L ;protected void doGet( HttpServletRequest request , HttpServletResponse response) throws ServletException , IOException {response .setContentType ( "text/html;charset=utf-8" );PrintWriter out = response .getWriter () ;out .println ( "----------来自TargetServlet的告白----------------<br />" ) ;out .print ( "我偷懒了,下面的响应数据并不是我自己产生的,而是包含的其它资源产生的<br/>" ) ;request .setAttribute ( "sharedatt", "I`m shared attribute") ;request .getRequestDispatcher ( "test.jsp?sharedparam=Im-shared-parameter" ). include (request , response ) ;out .flush () ;out .close () ;} }
<%@ page contentType= "text/html; charset=UTF-8" pageEncoding = "UTF-8" trimDirectiveWhitespaces = "true"session = "false" %><p> ------------------------来自test.jsp的告白-------------------------- </p> <p> 我输出的响应数据将被其它的资源包含 </p> <p> 从request中提取共享的属性Attribute : <%= request.getAttribute("s haredatt") %> <p> 从request中提取共享的参数Parameter : <%= request.getParameter("sharedparam" ) %>
参考:http://www.cnblogs.com/lulipro/