我试图完成以下作业：
用户在两个输入字段上写下其名称和年龄。 编写一个servlet，它返回一个html页面，servlet能够理解该用户是成人还是未成年人。 这就是我所做的：
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class hmIsAdult extends HttpServlet {
protected void doPost( HttpServletRequest request,
HttpServletResponse response )
throws ServletException, IOException
{
String firstName = request.getParameter( "firstname" );
String the_age = request.getParameter( "age" );
int age;
try {
age = Integer.parseInt(the_age);
}
catch (NumberFormatException e) {
age = 0;
}
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
out.println( "<?xml version = \"1.0\"?>" );
out.println( "<!DOCTYPE html PUBLIC \"-//W3C//DTD " +
"XHTML 1.0 Strict//EN\" \"http://www.w3.org" +
"/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );
out.println(
"<html xmlns = \"http://www.w3.org/1999/xhtml\">" );
out.println( "<head>" );
out.println( "<title>My first servlet</title>" );
out.println( "</head>" );
out.println( "<body>" );
out.println( "<h1>Hello " + firstName + ",</h1><br />" );
if (age < 18) {
out.println( "<h3>You are not an adult.</h3>" );
}
else {
out.println( "<h3>You are an adult.</h3>" );
}
out.println( "</body>" );
out.println( "</html>" );
out.close();
}
}
web.xml包含以下指令：
<servlet>
<servlet-name>homeworkIsAdult</servlet-name>
<display-name>homeworkIsAdult display name</display-name>
<description>homeworkIsAdult description</description>
<servlet-class>hmIsAdult</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>homeworkIsAdult</servlet-name>
<url-pattern>/homeworkIsAdult</url-pattern>
</servlet-mapping>
包含servlet调用的html文件是：
<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns = "http://www.w3.org/1999/xhtml">
<head>
<title>My first homework using servlet</title>
</head>
<body>
<form action = "/mydir/homeworkIsAdult" method = "post">
<p><label>Please insert your first name, your age and then press the Submit button<br />
<input type = "text" name = "firstname" />
<input type = "number" value = "0" step = "1" name = "age" />
<input type = "submit" value = "Submit" />
</p></label>
</form>
</body>
</html>
它按预期工作。
在下一步中我将使用cookie：servlet现在应该记住使用cookie的参数firstname和age。
然后，当用户是成年人时，servlet还需要询问其地址。同一个servlet应该使用另一个cookie重新记住该地址，并生成一个包含firstname，age和address的页面。
当用户是次要用户时，servlet应该将用户重定向（使用sendRedirect方法）到第二个servlet。第二个servlet应该读取cookie并写一条消息，例如＆＃34;亲爱的＆＃34; +名字+＆＃34;你无法访问这些内容＆＃34; 这就是我所做的。
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class hmIsAdultCookie extends HttpServlet {
protected void doPost( HttpServletRequest request,
HttpServletResponse response )
throws ServletException, IOException
{
String firstName = request.getParameter( "firstname" );
String the_age = request.getParameter( "age" );
int age;
try {
age = Integer.parseInt(the_age);
}
catch (NumberFormatException e) {
the_age = "0";
age = 0;
}
// IS IT OK TO GET THE PARAMETER ADDRESS HERE !?!?!
String address = request.getParameter( "address" );
if (address != null) {
Cookie cookie_address = new Cookie("address", address);
}
Cookie cookie_firstname = new Cookie("firstname", firstName);
Cookie cookie_age = new Cookie("age", the_age);
response.addCookie(cookie_firstname);
response.addCookie(cookie_age);
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
out.println( "<?xml version = \"1.0\"?>" );
out.println( "<!DOCTYPE html PUBLIC \"-//W3C//DTD " +
"XHTML 1.0 Strict//EN\" \"http://www.w3.org" +
"/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );
out.println("<html xmlns = \"http://www.w3.org/1999/xhtml\">" );
out.println( "<head>" );
out.println( "<title>My first servlet</title>" );
out.println( "</head>" );
out.println( "<body>" );
out.println( "<h1>Hello " + firstName + ",</h1><br />" );
if (age < 18) {
// How can I redirect directly and automatically to another servlet (hmIsMinor for example)?
response.sendRedirect("homeworkIsMinor");
}
else {
// The user should insert the address, it should be read and saved on another cookie by hmIsAdult
// servlet and produce a page with a report containing firstname, age and address.
out.println( "<form action = \"/mydir/homeworkIsAdult\" method = \"post\">" );
out.println( "<p><label>Give ve also the address and press the Submit button again<br />" );
out.println( "<input type = \"text\" name = \"address\" />" );
out.println( "<input type = \"submit\" value = \"Submit\" /></p></label></form>" );
}
out.println( "</body>" );
// end XHTML document
out.println( "</html>" );
out.close();
}
protected void doGet( HttpServletRequest request,
HttpServletResponse response )
throws ServletException, IOException
{
Cookie cookies[] = request.getCookies();
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
out.println( "<?xml version = \"1.0\"?>" );
out.println( "<!DOCTYPE html PUBLIC \"-//W3C//DTD " +
"XHTML 1.0 Strict//EN\" \"http://www.w3.org" +
"/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );
out.println("<html xmlns = \"http://www.w3.org/1999/xhtml\">" );
out.println( "<head>" );
out.println( "<title>My first servlet</title>" );
out.println( "</head>" );
out.println( "<body>" );
if ( cookies != null && cookies.length != 0 ) {
out.println( "<h3>You have cookies</h3>" );
for (int ii = 0; ii < cookies.length; ii++)
out.println( "cookie name: " + cookies[ii].getName() + " cookie value: " + cookies[ii].getValue() + "<br/>" );
}
else {
out.println( "<h3>You don't have cookies</h3>" );
}
out.println( "</body>" );
out.println( "</html>" );
out.close();
}
}
这是文件hmIsMinor.java，使用sendFedirect方法调用，如家庭作业所示。
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class hmIsMinor extends HttpServlet {
protected void doGet( HttpServletRequest request,
HttpServletResponse response )
throws ServletException, IOException
{
Cookie cookies[] = request.getCookies();
response.setContentType( "text/html" );
PrintWriter out = response.getWriter();
out.println( "<?xml version = \"1.0\"?>" );
out.println( "<!DOCTYPE html PUBLIC \"-//W3C//DTD " +
"XHTML 1.0 Strict//EN\" \"http://www.w3.org" +
"/TR/xhtml1/DTD/xhtml1-strict.dtd\">" );
out.println("<html xmlns = \"http://www.w3.org/1999/xhtml\">" );
out.println( "<head>" );
out.println( "<title>My first servlet</title>" );
out.println( "</head>" );
out.println( "<body>" );
if ( cookies != null && cookies.length != 0 ) {
out.println( "<h3>You have cookies</h3>" );
for (int ii = 0; ii < cookies.length; ii++)
out.println( "cookie name: " + cookies[ii].getName() + " cookie value: " + cookies[ii].getValue() + "<br/>" );
}
else {
out.println( "<h3>You don't have cookies</h3>" );
}
out.println( "</body>" );
out.println( "</html>" );
out.close();
}
}
web.xml文件的内容
<servlet>
<servlet-name>homeworkIsAdultCookie</servlet-name>
<display-name>homeworkIsAdultCookie display name</display-name>
<description>homeworkIsAdultCookie description</description>
<servlet-class>hmIsAdultCookie</servlet-class>
</servlet>
<servlet>
<servlet-name>homeworkIsMinor</servlet-name>
<display-name>homeworkIsMinor display name</display-name>
<description>homeworkIsMinor description</description>
<servlet-class>hmIsMinor</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>homeworkIsAdultCookie</servlet-name>
<url-pattern>/homeworkIsAdultCookie</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>homeworkIsMinor</servlet-name>
<url-pattern>/homeworkIsMinor</url-pattern>
</servlet-mapping>
我已经添加了另一个html文件（homeworkIsAdultCookie.html）。
<?xml version = "1.0"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns = "http://www.w3.org/1999/xhtml">
<head>
<title>Processing get requests with data</title>
</head>
<body>
<form action = "/mydir/homeworkIsAdultCookie" method = "post">
<p><label>
Type your first name and press the Submit button
<br />
<input type = "text" name = "firstname" />
<input type = "number" value = "0" step = "1" name = "age" />
<input type = "submit" value = "Submit" />
</p></label>
</form>
</body>
</html>
重定向似乎有效，但当用户是成年人时，我无法解决问题。
请问你能帮帮我吗？