Session管理
Session管理(Session追踪)是Web应用程序开发中一个非常重要的主题.
本篇文章将重点讲解常用的Session管理的四个方法:网址重写 隐藏域 cookie 及HttpSession对象.
1.网址重写
网址重写是一种Session追踪技术,需要将一个或多个token作为一个查询字符串添加到一个URL中.token的格式是键=值.
URL和token之间要用一个问号(?)隔开,两个token之间用一个&符号隔开.
如果token不必在过多的URL中四处携带,那么网址重写比较合适.它的缺点如下:
- 有的浏览器中,URL限制2000个字符.
- 仅当有链接要插入值时,值才能转换成后面的资源.此外,不容易将值插入到静态网页中.
- 网址重写必须在服务器端有效,所有链接都必须带有值,可能造成一个页面会有许多链接.
- 空格 &符号及问号都必须进行编码.
- URL中的信息是明显可见的.
网址重写栗子:
package app02a.urlrewriting;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
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(name = "Top10Servlet", urlPatterns = { "/top10" })
public class Top10Servlet extends HttpServlet {
private static final long serialVersionUID = 987654321L;
private List<String> londonAttractions;
private List<String> parisAttractions;
@Override
public void init() throws ServletException {
londonAttractions = new ArrayList<String>(10);
londonAttractions.add("Buckingham Palace");
londonAttractions.add("London Eye");
londonAttractions.add("British Museum");
londonAttractions.add("National Gallery");
londonAttractions.add("Big Ben");
londonAttractions.add("Tower of London");
londonAttractions.add("Natural History Museum");
londonAttractions.add("Canary Wharf");
londonAttractions.add("2012 Olympic Park");
londonAttractions.add("St Paul's Cathedral");
parisAttractions = new ArrayList<String>(10);
parisAttractions.add("Eiffel Tower");
parisAttractions.add("Notre Dame");
parisAttractions.add("The Louvre");
parisAttractions.add("Champs Elysees");
parisAttractions.add("Arc de Triomphe");
parisAttractions.add("Sainte Chapelle Church");
parisAttractions.add("Les Invalides");
parisAttractions.add("Musee d'Orsay");
parisAttractions.add("Montmarte");
parisAttractions.add("Sacre Couer Basilica");
}
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
String city = request.getParameter("city");
if (city != null &&
(city.equals("london") || city.equals("paris"))) {
// show attractions
showAttractions(request, response, city);
} else {
// show main page
showMainPage(request, response);
}
}
private void showMainPage(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head>" +
"<title>Top 10 Tourist Attractions</title>" +
"</head><body>" + ""
"Please select a city:" +
"<br/><a href='?city=london'>London</a>" +
"<br/><a href='?city=paris'>Paris</a>" +
"</body></html>");
}
private void showAttractions(HttpServletRequest request,
HttpServletResponse response, String city)
throws ServletException, IOException {
int page = 1;
String pageParameter = request.getParameter("page");
if (pageParameter != null) {
try {
page = Integer.parseInt(pageParameter);
} catch (NumberFormatException e) {
// do nothing and retain default value for page
}
if (page > 2) {
page = 1;
}
}
List<String> attractions = null;
if (city.equals("london")) {
attractions = londonAttractions;
} else if (city.equals("paris")) {
attractions = parisAttractions;
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<html><head>" +
"<title>Top 10 Tourist Attractions</title>" +
"</head><body>");
writer.println("<a href='top10'>Select City</a> ");
writer.println("<hr/>Page " + page + "<hr/>");
int start = page * 5 - 5;
for (int i = start; i < start + 5; i++) {
writer.println(attractions.get(i) + "<br/>");
}
writer.print("<hr style='color:blue'/>" +
"<a href='?city=" + city +
"&page=1'>Page 1</a>");
writer.println(" <a href='?city=" + city +
"&page=2'>Page 2</a>");
writer.println("</body></html>");
}
}最值得关注的是a标签的href属性值,它包含一个问号,接着是token:city=london或着city=paris.任何相对的URL(没有协议部分的URL)都会被当作是相对于当前页面的URL,如果点击页面的某一个超链接,那么:
或者
就会被发送到服务器.
运行效果:
初始页:
伦敦前十大旅游地中的第一页:
伦敦十大旅游地的第二页:
隐藏域
利用隐藏域来保存状态,与采用网址重写技术类似.只是它不把值放到URL后面,而是放到HTML表单的隐藏域中.
优点是: 将更多的字符传到服务器,不需要进行字符编码.
缺点是:只有当要传递的信息不需要跨越多个页面时,才适合使用这个技术.
隐藏域栗子:
Customer类构建一个客户模型:
package app02a.hiddenfields;
public class Customer {
private int id;
private String name;
private String city;
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
}利用隐藏域来更新客户信息:
package app02a.hiddenfields;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/*
* Not thread-safe. For illustration purpose only
*/
@WebServlet(name = "CustomerServlet", urlPatterns = {
"/customer", "/editCustomer", "/updateCustomer"})
public class CustomerServlet extends HttpServlet {
private static final long serialVersionUID = -20L;
private List<Customer> customers = new ArrayList<Customer>();
@Override
public void init() throws ServletException {
Customer customer1 = new Customer();
customer1.setId(1);
customer1.setName("Donald D.");
customer1.setCity("Miami");
customers.add(customer1);
Customer customer2 = new Customer();
customer2.setId(2);
customer2.setName("Mickey M.");
customer2.setCity("Orlando");
customers.add(customer2);
}
private void sendCustomerList(HttpServletResponse response)
throws IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<html><head><title>Customers</title></head>"
+ "<body><h2>Customers </h2>");
writer.println("<ul>");
for (Customer customer : customers) {
writer.println("<li>" + customer.getName()
+ "(" + customer.getCity() + ") ("
+ "<a href='editCustomer?id=" + customer.getId()
+ "'>edit</a>)");
}
writer.println("</ul>");
writer.println("</body></html>");
}
private Customer getCustomer(int customerId) {
for (Customer customer : customers) {
if (customer.getId() == customerId) {
return customer;
}
}
return null;
}
private void sendEditCustomerForm(HttpServletRequest request,
HttpServletResponse response) throws IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
int customerId = 0;
try {
customerId =
Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e) {
}
Customer customer = getCustomer(customerId);
if (customer != null) {
writer.println("<html><head>"
+ "<title>Edit Customer</title></head>"
+ "<body><h2>Edit Customer</h2>"
+ "<form method='post' "
+ "action='updateCustomer'>");
writer.println("<input type='hidden' name='id' value='"
+ customerId + "'/>");
writer.println("<table>");
writer.println("<tr><td>Name:</td><td>"
+ "<input name='name' value='" +
customer.getName().replaceAll("'", "'")
+ "'/></td></tr>");
writer.println("<tr><td>City:</td><td>"
+ "<input name='city' value='" +
customer.getCity().replaceAll("'", "'")
+ "'/></td></tr>");
writer.println("<tr>"
+ "<td colspan='2' style='text-align:right'>"
+ "<input type='submit' value='Update'/></td>"
+ "</tr>");
writer.println("<tr><td colspan='2'>"
+ "<a href='customer'>Customer List</a>"
+ "</td></tr>");
writer.println("</table>");
writer.println("</form></body>");
} else {
writer.println("No customer found");
}
}
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
String uri = request.getRequestURI();
if (uri.endsWith("/customer")) {
sendCustomerList(response);
} else if (uri.endsWith("/editCustomer")) {
sendEditCustomerForm(request, response);
}
}
@Override
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
// update customer
int customerId = 0;
try {
customerId =
Integer.parseInt(request.getParameter("id"));
} catch (NumberFormatException e) {
}
Customer customer = getCustomer(customerId);
if (customer != null) {
customer.setName(request.getParameter("name"));
customer.setCity(request.getParameter("city"));
}
sendCustomerList(response);
}
}运行效果:
客户列表:
Edit Customer表单:
注意到表单中的隐藏域没有?它包含了customer id,因此当提交表单时,服务器就会知道正在编辑哪个客户的信息
writer.println(“< input type=’hidden’ name=’id’ value=’” + customerId + “’/>”);
cookie
网址重写和隐藏域都只试用于保持那些不需要跨越许多页面的信息.
cookie是自动地在web服务器与浏览器之间来回传递的一小块信息,需要根据自己的需要来设置cookie的有效期.每台web服务器最多可以支持20个cookie.
它存在于javax.servlet.http.Cookie类
Cookie的创建方法:
Cookie cookie=new Cookie(name,value);
创建Cookie之后,要设置它的domain path maxAge属性,尤其maxAge它是Cookie的有效期.
之后需要用HttpServletResponse调用add方法,将Cookie发送到浏览器.
使用HttpServletResponse调用getCookies方法获得Cookie它返回的是Cookie数组,如果没有Cookie将返回NULL.
获取Cookie栗子:
Cookie[] cookies = request.getCookies();
Cookie maxRecordsCookie = null;
if (cookies != null) {
for (Cookie cookie : cookies) {
if (cookie.getName().equals("maxRecords")) {
maxRecordsCookie = cookie;
break;
}
}
}很遗憾,没有像getCookieByName这样的方法直接获取Cookie,更闹心的是,也没有直接删除Cookie的方法.要删除Cookie需要创建一个同名的Cookie,将它的maxAge属性设置为0,并在HttpServletResponse中添加一个新的cookie.
删除Cookie栗子:
Cookie cookie = new Cookie("userName", "");
cookie.setMaxAge(0);
response.addCookie(cookie);接下来写个完整使用Cookie的栗子:
PreferenceServlet类:
该类的作用是允许用户修改4个cookie的值,从而在同一个应用程序中设定其他Servlet的显示设置
package app02a.cookie;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "PreferenceServlet",
urlPatterns = { "/preference" })
public class PreferenceServlet extends HttpServlet {
private static final long serialVersionUID = 888L;
public static final String MENU =
"<div style='background:#e8e8e8;"
+ "padding:15px'>"
+ "<a href='cookieClass'>Cookie Class</a> "
+ "<a href='cookieInfo'>Cookie Info</a> "
+ "<a href='preference'>Preference</a>" + "</div>";
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head>" + "<title>Preference</title>"
+ "<style>table {" + "font-size:small;"
+ "background:NavajoWhite }</style>"
+ "</head><body>"
+ MENU
+ "Please select the values below:"
+ "<form method='post'>"
+ "<table>"
+ "<tr><td>Title Font Size: </td>"
+ "<td><select name='titleFontSize'>"
+ "<option>large</option>"
+ "<option>x-large</option>"
+ "<option>xx-large</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td>Title Style & Weight: </td>"
+"<td><select name='titleStyleAndWeight' multiple>"
+ "<option>italic</option>"
+ "<option>bold</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td>Max. Records in Table: </td>"
+ "<td><select name='maxRecords'>"
+ "<option>5</option>"
+ "<option>10</option>"
+ "</select></td>"
+ "</tr>"
+ "<tr><td rowspan='2'>"
+ "<input type='submit' value='Set'/></td>"
+ "</tr>"
+ "</table>" + "</form>" + "</body></html>");
}
@Override
public void doPost(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
String maxRecords = request.getParameter("maxRecords");
String[] titleStyleAndWeight = request
.getParameterValues("titleStyleAndWeight");
String titleFontSize =
request.getParameter("titleFontSize");
response.addCookie(new Cookie("maxRecords", maxRecords));
response.addCookie(new Cookie("titleFontSize",
titleFontSize));
// delete titleFontWeight and titleFontStyle cookies first
// Delete cookie by adding a cookie with the maxAge = 0;
Cookie cookie = new Cookie("titleFontWeight", "");
cookie.setMaxAge(0);
response.addCookie(cookie);
cookie = new Cookie("titleFontStyle", "");
cookie.setMaxAge(0);
response.addCookie(cookie);
if (titleStyleAndWeight != null) {
for (String style : titleStyleAndWeight) {
if (style.equals("bold")) {
response.addCookie(new
Cookie("titleFontWeight", "bold"));
} else if (style.equals("italic")) {
response.addCookie(new Cookie("titleFontStyle",
"italic"));
}
}
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.println("<html><head>" + "<title>Preference</title>"
+ "</head><body>" + MENU
+ "Your preference has been set."
+ "<br/><br/>Max. Records in Table: " + maxRecords
+ "<br/>Title Font Size: " + titleFontSize
+ "<br/>Title Font Style & Weight: ");
// titleStyleAndWeight will be null if none of the options
// was selected
if (titleStyleAndWeight != null) {
writer.println("<ul>");
for (String style : titleStyleAndWeight) {
writer.print("<li>" + style + "</li>");
}
writer.println("</ul>");
}
writer.println("</body></html>");
}
}运行效果:
用cookie管理用户偏好:
CookieClassServlet类
该类的作用将Cookie类的属性写在一个Html列表中,列表中的项编号由maxRecords cookie的值决定.这个值由PreferenceServlet来设置.
package app02a.cookie;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "CookieClassServlet",
urlPatterns = { "/cookieClass" })
public class CookieClassServlet extends HttpServlet {
private static final long serialVersionUID = 837369L;
private String[] methods = {
"clone", "getComment", "getDomain",
"getMaxAge", "getName", "getPath",
"getSecure", "getValue", "getVersion",
"isHttpOnly", "setComment", "setDomain",
"setHttpOnly", "setMaxAge", "setPath",
"setSecure", "setValue", "setVersion"
};
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
Cookie[] cookies = request.getCookies();
Cookie maxRecordsCookie = null;
if (cookies != null) {
for (Cookie cookie : cookies) {
if (cookie.getName().equals("maxRecords")) {
maxRecordsCookie = cookie;
break;
}
}
}
int maxRecords = 5; // default
if (maxRecordsCookie != null) {
try {
maxRecords = Integer.parseInt(
maxRecordsCookie.getValue());
} catch (NumberFormatException e) {
// do nothing, use maxRecords default value
}
}
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head>" + "<title>Cookie Class</title>"
+ "</head><body>"
+ PreferenceServlet.MENU
+ "<div>Here are some of the methods in " +
"javax.servlet.http.Cookie");
writer.print("<ul>");
for (int i = 0; i < maxRecords; i++) {
writer.print("<li>" + methods[i] + "</li>");
}
writer.print("</ul>");
writer.print("</div></body></html>");
}
}运行效果:
CookieClassServlet的输出结果:
CookieInfoServlet类:
package app02a.cookie;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.Cookie;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
@WebServlet(name = "CookieInfoServlet", urlPatterns = { "/cookieInfo" })
public class CookieInfoServlet extends HttpServlet {
private static final long serialVersionUID = 3829L;
@Override
public void doGet(HttpServletRequest request,
HttpServletResponse response) throws ServletException,
IOException {
Cookie[] cookies = request.getCookies();
StringBuilder styles = new StringBuilder();
styles.append(".title {");
if (cookies != null) {
for (Cookie cookie : cookies) {
String name = cookie.getName();
String value = cookie.getValue();
if (name.equals("titleFontSize")) {
styles.append("font-size:" + value + ";");
} else if (name.equals("titleFontWeight")) {
styles.append("font-weight:" + value + ";");
} else if (name.equals("titleFontStyle")) {
styles.append("font-style:" + value + ";");
}
}
}
styles.append("}");
response.setContentType("text/html");
PrintWriter writer = response.getWriter();
writer.print("<html><head>" + "<title>Cookie Info</title>"
+ "<style>" + styles.toString() + "</style>"
+ "</head><body>" + PreferenceServlet.MENU
+ "<div class='title'>"
+ "Session Management with Cookies:</div>");
writer.print("<div>");
// cookies will be null if there's no cookie
if (cookies == null) {
writer.print("No cookie in this HTTP response.");
} else {
writer.println("<br/>Cookies in this HTTP response:");
for (Cookie cookie : cookies) {
writer.println("<br/>" + cookie.getName() + ":"
+ cookie.getValue());
}
}
writer.print("</div>");
writer.print("</body></html>");
}
}运行效果:
CookieInfoServlet的输出结果:
Servlet相对路径和绝对路径
一、JSP跳转到Servlet
1、相对路径,如href=”servlet/TestServlet”
*注意：如果写成”/servlet/TestServlet”会报错，因为第一个’/’表示的是【服务器根目录：http://localhost:8080/】
2、绝对路径，通过内置成员变量path实现，如href=”<%=path%>/servlet/TestServlet”。
*注意：这里的path得到的是项目根目录，如【http://localhost:8080/Servlet002_GetFormDemo】
二、Servlet跳转JSP
1、请求重定向：response.sendRedirect(request.getContextPath()+”/xxx.jsp”);这里通过request.getContextPath()方法获得项目根目录，或者通过”../xxx.jsp”取得上层路径得到
2、服务器内部转发：request.getRequestDispatcher(“../xxx.jsp”).forward(req,resp);
*小结：都可以通过../xxx.jsp得到
一、JSP跳转到Servlet
1、相对路径,如href=”servlet/TestServlet”
*注意：如果写成”/servlet/TestServlet”会报错，因为第一个’/’表示的是【服务器根目录：http://localhost:8080/】
2、绝对路径，通过内置成员变量path实现，如href=”<%=path%>/servlet/TestServlet”。
*注意：这里的path得到的是项目根目录，如【http://localhost:8080/Servlet002_GetFormDemo】
二、Servlet跳转JSP
1、请求重定向：response.sendRedirect(request.getContextPath()+”/xxx.jsp”);这里通过request.getContextPath()方法获得项目根目录，或者通过”../xxx.jsp”取得上层路径得到
2、服务器内部转发：request.getRequestDispatcher(“../xxx.jsp”).forward(req,resp);
*小结：都可以通过../xxx.jsp得到
三、web.xml配置中
< url-pattern>/servlet/HelloWorld < /url-pattern>: url-pattern处必须以 / 开头，这里/ 表示项目的根目录
在Servlet中重定向要使用获得上下文对象。getContextPath()+”/文件名。jsp”
在Servlet中如果用服务器跳转，getRequestDispatcher(“/文件.jsp”)或者getRequestDispatcher(“../文件.jsp”)采用逆向思维，获取当前目录的上一层目录
超链接的第一个斜线表示的是服务器的根目录；servlet前边打斜线，表示到根目录下打开servlet项目
利用request.getContextpath()，其代表项目的根目录
url-pattern处的斜线代表项目的根目录,必须添加
response.sendRedirect当前路径是ServletPathDirection/servlet/
服务器内部跳转，斜线代表项目根目录
Ps1：路径前缀不写相当于“./”，如“test.jsp”==“./test.jsp”
Ps2：
Ps3：更新项目名的时候注意，先检查是否在myeclipse 2015的空间包里（不是也没关系其实，最好放在这里面），然后项目——属性——MyEclipse——Project Facets——Web——Web Context-root：（服务器项目名），对应的文件夹在D:\空间名.metadata.me_tcat7\work\Catalina\localhost\Xxx——文件夹名就是服务器项目名。（注意：修改文件夹名字并不会修改服务器项目名，而修改Web Context-root才会对服务器项目名起作用）。若是类似myeclipse8.5的版本，则直接在Tomcat——webapps——项目文件夹名即是Web服务器项目名，而且修改文件夹名就会影响Web服务器项目名。
1、服务器内部跳转，这里的斜线表示项目的根目录
2.请求重定向跳转，这里的斜线表示当前目录
3.超链接和表单跳转，这里的第一个斜线表示服务器根目录，不加斜线就是当前目录
4.request.getContextPath();表示当前项目根目录