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);
}
}