Recipe 20.8 Reading a Received Email s Headers from a Servlet

Recipe 20.8 Reading a Received Email's Headers from a Servlet

Problem

You want to read the headers from an email in a servlet.

Solution

Use the JavaMail API to access each email message. Call the getAllHeaders( ) method of the Part interface, then iterate through the Enumeration return value to get the name and value of each header.

Discussion

An advanced email program, such as a spam filter, is designed to examine an email's headers, not just its message and file attachments.

A header is composed of a name, a colon character (:), and a value. The headers provide details about the email message, such as who sent the message and the mail server(s) that handled the message during its network travels . An example header is:

 To: <bwperry@parkerriver.com>

The JavaMail API makes it easy to list an email's headers. The Message object has a getAllHeaders( ) method (via the Part interface that the Message class implements). This method returns a java.util.Enumeration , holding a collection of javax.mail.Header objects. To get the header name and value from these Header objects, just call their getName( ) and getValue( ) methods .

The Part interface also has a getHeader(String headerName) method that you can use to obtain the value for a particular header. This method returns a String array containing the value(s) for the header of that name.

Example 20-9 shows the same servlet from Recipe 20.4, revised to list both the message contents and the header values. The header- related code appears in the displayMessage( ) method.

Example 20-9. A servlet displays email header names and values

 package com.jspservletcookbook;     import java.io.IOException; import java.io.PrintWriter; import java.util.Properties; import java.util.Enumeration;  import javax.mail.*; import javax.mail.internet.*;  import javax.servlet.*; import javax.servlet.http.*; public class HeaderAccessor extends HttpServlet {    private final static String DEFAULT_SERVER = "mail.attbi.com";   public void doGet(HttpServletRequest request,      HttpServletResponse response) throws ServletException,       java.io.IOException {          response.setContentType("text/html");     java.io.PrintWriter out = response.getWriter( );     out.println("<html><head><title>Email Reader</title></head><body>");  handleMessages(request, out);  out.println("</body></html>");   } //doGet         private void handleMessages(HttpServletRequest request,       PrintWriter out) throws IOException, ServletException {            HttpSession httpSession =  request.getSession( );       String user = (String) httpSession.getAttribute("user");       String password = (String) httpSession.getAttribute("pass");       String popAddr = (String) httpSession.getAttribute("pop");       Store popStore = null;       Folder folder = null;           if (! check(popAddr))           popAddr = HeaderAccessor.DEFAULT_SERVER;            try {              if ((! check(user))  (! check(password)))              throw new ServletException(              "A valid username and password is required to check email.");               Properties properties = System.getProperties( );           Session session = Session.getDefaultInstance(properties);           popStore = session.getStore("pop3");           popStore.connect(popAddr, user, password);           folder = popStore.getFolder("INBOX");           if (! folder.exists( ))               throw new ServletException(               "An 'INBOX' folder does not exist for the user.");                   folder.open(Folder.READ_ONLY);           Message[] messages = folder.getMessages( );           int msgLen = messages.length;             if (msgLen == 0)              out.println(              "<h2>The INBOX folder does not yet contain any " +              "email messages.</h2>");             for (int i = 0; i < msgLen; i++){  displayMessage(messages[i], out);  out.println("<br /><br />");          }//for         } catch (Exception exc) {              out.println(           "<h2>Sorry, an error occurred while accessing the " +           "email messages.</h2>");         out.println(exc.toString( ));              } finally {         try{             if (folder != null)                 folder.close(false);                          if (popStore != null)                popStore.close( );         } catch (Exception e) { }     }   }//handleMessages  private void displayMessage(Message msg, PrintWriter out)        throws MessagingException, IOException{  if (msg != null && msg.getContent( ) instanceof String){                     if (msg.getFrom( )[0] instanceof InternetAddress){               out.println(               "Message received from: " +               ((InternetAddress)msg.getFrom( )[0]).getAddress( ) +"<br />");          }          out.println("Message content type: " + msg.getContentType( ) +            "<br />");          out.println(            "Message body content: " + (String) msg.getContent( ));  //List each of the email headers using a ul tag          out.println("<ul>");          Header head = null;          Enumeration headers = msg.getAllHeaders( );                    while ( headers.hasMoreElements( ) ){              head = (Header) headers.nextElement( );              out.println(                "<li>" + head.getName( ) + ": " + head.getValue( )+ "</li>");          }//while  out.println("</ul>");                 } else{                    out.println(             "<h2>The received email message was not " +             "a text content type.</h2>");       }             }//displayMessage        private boolean check(String value){            if(value == null  value.equals(""))       return false;                    return true;     } }

Figure 20-3 shows the browser display of the servlet in Example 20-9. Each of the headers is preceded by a bullet character, followed by the header name, a colon, and the header value.

Figure 20-3. A servlet accesses an email and displays its header s

Recipe 20.8 Reading a Received Email s Headers from a Servlet