Develop WebMail system using JSP

Author：Eve Cole Update Time：2009-07-02 17:12:05

Email (E-mail) is one of the most widely used services on the Internet. The traditional Email application model is based on the C/S structure, that is, users use the client's email sending and receiving tools (such as Outlook, Foxmail, etc.) and the server that provides email services. (such as 163.net, 263.net, 371.net) communication, before using the client mail tool, the user must make some necessary settings, such as specifying the host address and communication port of the mail server, etc. These tasks are very important for those who have just started surfing the Internet. Users will have certain difficulties. If email and Web are combined, that is, through Web programming and appropriate system settings, users can obtain and use complete email services just by accessing the Web. This will be extremely difficult. It is convenient for Internet users. This system is called WebMail. WebMail is currently one of the most popular services on the Internet and one of the essential features for many websites. In addition, WebMail is also suitable for enterprise or campus network applications.

The WebMail system is usually implemented after the backend server is built and set up, while the frontend development work is mainly about the interaction between development tools and the backend database and mail server. The stability and reliability of various server software running on the Linux platform have always been very good, and the selection of cross-platform Java development tools makes the system more stable and more scalable.

JSP performance

Although the powerful functions provided by JSP are built on Servlet, the performance of JSP is almost the same as that of Servlet. JSP must first be compiled into a Servlet, which only adds a small amount of code. It only needs to be compiled once and can be precompiled, which eliminates unnecessary burden on runtime. The difference in performance between JSP and Servlet is only that the returned data is binary. This is because JSP uses PrintWriter when returning, and Servlet can be applied to the faster OutputStream.

JSP's custom tag library can encapsulate a large number of complex Java operations in a Form. These predefined tags can be easily called by those without Java knowledge. Therefore, JSP's custom tag library can effectively divide the work of Java programmers and Web designers. However, for every tag applied to the page, the web container must create a new tag handle object or extract it from the tag buffer. Therefore, applying too many customized tags will cause unnecessary waste of resources.

BodyTags are special custom tags that can extract content encapsulated between them or replace that content. The content between BodyTags is generally backed up in memory. Since BodyTags can be nested and repeated, applying multiple levels of BodyTags in a program will occupy a lot of valuable memory and system resources.

Implement the main functions of WebMail

The system provides the functions of obtaining, reading, writing, forwarding, replying, printing, deleting and user management. Considering the cross-platform nature of the system, Java and related technology products are used as development tools, especially JSP as the service program. This way, there are no other requirements for the client. At the same time, the performance of the system is further improved under high load. The entire WebMail system uses pure Java code. The server starts a thread every time it responds to a service request, instead of starting a process like CGI. This can save system resources and improve system performance.

Implement the main code

Get the information entered by the user

The function of obtaining user input content is implemented through the getParameter method. The input text content can be obtained on the server side through the following code. The program code is as follows:

String username=request.getParameter("login");
String password=request.getParameter("password");
Session session2=Session.getInstance(System.getProperties(),null);
Store store=session2.getStore("pop3");

To connect to the server based on the information entered by the user, the program code is as follows:

try{
 store.connect(host,username+"%nyist.net", password);
}
catch(javax.mail.AuthenticationFailedException e)
{content="Username and password do not match";}

Receive email code snippet

To connect to the server based on obtaining the information entered by the user, the code is:

store.connect("nyist.net",-1,request.getParameter("username")+"%nyist.net",request
.getParameter("password"));

To obtain server-side information, the code is as follows:

Folder folder = store.getFolder("INBOX");
Folder.open (Folder.READ_WRITE);
Message message[]=folder.getMessages();
FetchProfile fp=new FetchProfile();
fp.add(FetchProfile.Item.ENVELOPE);
fp.add(FetchProfile.Item.FLAGS);
fp.add("X-Mailer");
folder.fetch(message,fp);

Depending on the format of the information on the server, different methods are used to read:

String contentbody="";
Object o=message[j].getContent();

If its Type is tex/plain, it can be read directly. The code is as follows:

if (message[j].isMimeType("text/plain")) 
{
 contentbody=(String)+"</td>";
 StringBuffer buf=new StringBuffer(contentbody.length()+6);
 char ch=' ';
 for(int p=0;p<contentbody.length();p++)//If a newline is encountered, convert to <br>
 {ch=contentbody.charAt(p);
  if(ch=='n')buf.append("<br>");
  else buf.append(ch);
 }
 contentbody=buf.toString();
}

If the information type is text/html, different information types are processed in slightly different ways (as shown in the code snippet). Due to limited space, I will not explain them one by one.

else if (message[j].isMimeType("text/html")) 
 contentbody=(String)o+"</td>";

Send email code snippet

According to the content entered by the user, the code to obtain the email header information is as follows:

String host = "nyist.net";
String from = request.getParameter("from");
String to = request.getParameter("to");
String subject = request.getParameter("subject");
String content = request.getParameter("content");
Properties props = System.getProperties();
//Set the mail service props.put("mail.smtp.host", host);
Session session2 =Session.getInstance(props, null);

The code to set the email header information is as follows:

MimeMessage message =new MimeMessage(session2);
message.setFrom(new InternetAddress(from));
message.addRecipient(Message.RecipientType.TO,new InternetAddress(to));
message.setSubject(subject);
message.setSentDate(new Date());
// create the message part
MimeBodyPart messageBodyPart =new MimeBodyPart();

Set the email content and build the program segment as follows:

messageBodyPart.setText(content);
Multipart multipart = new MimeMultipart();
multipart.addBodyPart(messageBodyPart);

Users often include attachments when sending emails, which is to transfer files local to the browser client user to the POP client. The implementation code is as follows:

for (int i=0;i<mySmartUpload.getFiles().getCount();i++)
{
 com.jspsmart.upload.File myFile = mySmartUpload.getFiles().getFile(i);
 if (!myFile.isMissing()) {
 myFile.saveAs("/upload/" + myFile.getFileName()); 
 count++;
}

While uploading attachments, count the number of uploaded files and display them on the screen through out.println ("Uploaded" + count + "files").

If there are attachments in the sent letter, use the following code to send it:

for(int i=0;request.getParameter("file"+i)!=null;i++)
{
 messageBodyPart = new MimeBodyPart();
 File file=new File("/home/mengyu/ROOT/upload/",request.getParameter("file"+i));
 DataSource source =new FileDataSource(file);
 messageBodyPart.setDataHandler(new DataHandler(source));
 messageBodyPart.setFileName(request.getParameter("file"+i));
 multipart.addBodyPart(messageBodyPart);
}
// Put parts in message
message.setContent(multipart);

Call the send method of Transport to send the constructed MIME Message object. The code is as follows:

Transport.send(message);

Remove email snippet

In the process of using email through the web interface, it is often necessary to delete received spam emails or emails that have been viewed. This is also an essential function in email, so we have designed a corresponding method for deleting emails in the web interface. Function, the main program code segments are as follows:

Folder folder=store.getFolder("INBOX");
folder.open(Folder.READ_WRITE);
Message message[]=folder.getMessages();
String msg[]=request.getParameterValues("msg");
for(int i=0,n=msg.length;i<n;i++)
 message[Double.valueOf(msg[i]).intValue()].setFlag(Flags.Flag.DELETED,true);
folder.close(true);

User management

In the process of running the system, add users through the management interface, delete unnecessary users, and change the user's password. This is a necessary module during the running of the program. The code is as follows:

//Add userRuntime.getRuntime().exec("/home/vpopmail/bin/vadduser"+request.getParameter("user
name")+"@nyist.net "+request.getParameter("passwd"));
//Delete userRuntime.getRuntime().exec("/home/vpopmail/bin/vdeluser"+request.getParameter("user
name")+"@nyist.net");
//Modify user password Runtime.getRuntime().exec("/home/vpopmail/bin/vpasswd"+request.getParameter("usern
ame")+"@nyist.net "+request.getParameter("passwd"));

Summarize

Java simplifies the complex issues related to the development, deployment and management of enterprise solutions. It is an object-oriented programming language and a platform-independent, high-performance server-side programming language. The standard system framework and services it provides are suitable for group development, have good controllability, and are well integrated with other resources. It is of great significance to use Java as a programming tool to develop a high-performance, high-availability WebMail server.