servlet session管理的四种方式--一 url重写

servlet对于多页面共享信息提供四种方式。

1.url重写的方式

在下面的例子中，每一次请求都通过doGet方法进行“分流”。

如果在网址中含有参数city且不为空，就调用showAttribute()方法下所包含的servlet页面,如果没有该参数或该参数对应值为空，则调用mainPage()方法下的页面。

if (request.getParameter("city") != null){
.......
.......
showAttribute(request, response, city, page);
}esle showMainPage(request, response)

在执行showMainPage()方法中，可以通过选择选项，进行url重写

选择不同的选项，其后添加??city=london&page=1或者?city=pairs&page=1,url改写为localhost:8080/Rewrite?city=london&page=1或localhost:8080/Rewrite?city=pairs&page=1重新调用doGet方法，因为其含有city参数且不为空，不再调用showMainpage()方法，改为调用showAttribute(request, response, city, page)方法，实现了多页面共享信息的目的。

pw.println("<html><head><title>select a city</title><head><body>"
				 + "<h3><a href="?city=london&page=1">london</a><h3>"
				 + "<h3><a href="?city=pairs&page=1">pairs</a><h3>"
				 + "</body></html>");

import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebServlet("/Rewrite")
public class Rewrite extends HttpServlet {
	private static final long serialVersionUID = 1L;
    public Rewrite() {
        super();
    }
    
    ArrayList<String> londonAttr = new ArrayList<>(10);
    ArrayList<String> pairsAttr = new ArrayList<>(10);
    
    public void init() throws javax.servlet.ServletException{
    	for( int i = 0; i < 10; i++) {
    		londonAttr.add("l " + (i+1));
    	}
    	
    	for( int i = 0; i < 10; i++) {
    		pairsAttr.add("p " + (i+1));
    	}
    }

	protected void doGet(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		if(request.getParameter("city") != null) {
			System.out.println("attribute");
			String city = request.getParameter("city");
			int page = 1;
			int p = 1;
			if (request.getParameter("page") != null){
			    try {
			        p = Integer.parseInt(request.getParameter("page"));
			        //showAttribute(request, response, city, page);
			    }catch (NumberFormatException e) {}
			}
			page = p;
			showAttribute(request, response, city, page);
		}else showMainPage(request, response);
	}
	
	public void showMainPage(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException{
		response.setContentType("text/html");
		PrintWriter pw = response.getWriter();
		pw.println("<html><head><title>select a city</title><head><body>"
				 + "<h3><a href="?city=london&page=1">london</a><h3>"
				 + "<h3><a href="?city=pairs&page=1">pairs</a><h3>"
				 + "</body></html>");
	}
	
	public void showAttribute(HttpServletRequest request, HttpServletResponse response, String city, int page)
			throws ServletException, IOException {
		response.setContentType("text/html");
		PrintWriter pw = response.getWriter();
		pw.println("<html><head><title>" + city +"</title></head><body>"
				 + "<table>");
		if(city.equals("london")) {
			for (int i = 5 * (page-1) ; i < 5 * (page-1) + 5; i++) {
				pw.println("<tr><td>" + londonAttr.get(i) + "</td><tr>");
			}
		}else if(city.equals("pairs")) {
			for (int i = 5 * (page-1) ; i < 5 * (page-1) + 5; i++) {
				pw.println("<tr><td>" + pairsAttr.get(i) + "</td><tr>");
			}
		}
		pw.println("</table>");
		if(page == 1) pw.println("<a href=?city=" + city + "&page=2>next</a><br/>");
		if(page == 2) pw.println("<a href=?city=" + city + "&page=1>pass</a><br/>");
		pw.println("<a href=http://localhost:8080/goon/Rewrite>city list</a>");
		pw.println("</body><html>");
	}
	
	protected void doPost(HttpServletRequest request, HttpServletResponse response) 
			throws ServletException, IOException {
		doGet(request, response);
	}

}