How to create a Servlet

Question

Hello All,
I am trying to learn creating a servlet in oaf. Although I kind of understand the concept of a servlet....have doubts about where the servlet class file lives/resides? Does it matter where it resides....at least for now in the Jdeveloper environment?
The way I understand it is:
1) In the oaf page need to place the item in which the servlet result is displayed
2) In the PR of the CO of the above page, need to find the above item
2.1) set the source of the above item to be the servlet class while passing in the params into the set source call.
2.2) Does it matter where the servlet class file resides? ie., can it live anywhere in the project??
Pls. help me understand this concept.
Practially in steps2,3 of the servlet wizard of the Jdeveloper what do these do?
Step#2: URL Pattern
Step#3: Parameters. Do I have to necessarily set up the params here in this step or can they be dynamically set when the serveletis invoked in the PR of the CO? If yes, could you pls. provide a sample code. If params can be done either way...which way is effective. Reason for asking is....in my other post, I mentioned that while trying to create a dynamic VO, it seemed to force me to explicitly set the sql statement instead of simply running the sql statement associate with the VO of the page (I am not sure why it is like that...but that worked)
Thanks,
Edited by: OAF_Monkey on Nov 16, 2012 4:11 PM

Answer 1

The way I understand (after following several older posts) is
1) When my destination page (say page2 renders), in the CO need to find the image item/bean (I am assuming bean and an item mean the same)
2) After finding the item item/bean, need to set its source as "ReadImage" telling it to go get it from the web.xml while passing in the id
for which it needs to find an image/blob in the db.
At this point, if it finds the class "ReadImage" then it should get the
2.1)db connection
2.2)get the parameter passed in using
      String image_id = request.getParameter("s1");
     2.3)get the sql statement provided
2.4)get the image/blob as an input stream and write to the output stream using the below
        InputStream in = null;
        in = rs.getBinaryStream("IMAGE");
     Below is my code in the PR of CO
      System.out.println("I am back in the IMG CO : primaykey val is "+ s1 );
BP1-->  OAImageBean imageItem = (OAImageBean)webBean.findIndexedChildRecursive("SJImage");
      System.out.println("I am back in the IMG CO1 : after finding the image item" );
BP2-->     if (imageItem !=null ){
      System.out.println("I am back in the IMG CO2 : before setting the source of the image item" );    
BP3-->     imageItem.setSource("/OA_HTML/WEB-INF/ReadImage?id=" + s1);
      System.out.println("I am back in the IMG CO3 : after setting the source of the image item" + imageItem.getSource());
      }When I ran it in the debug mode (break points shown above BP1,2,3), I can see that the value is getting passed in ok with the 's1' at BP1 and BP2.
However when it reaches BP3, if I expand all the nodes of the debug window, I can see that in the 'Statisfields of the CO', it shows
"Failed to establish the database connection." for the "DBCONNECT_ERROR_MSG" node.
In the "ReadImage" class file the code to get connection is shown below:
    public void init(ServletConfig config) throws ServletException {
        super.init(config);
        try
        Class.forName("oracle.jdbc.driver.OracleDriver");
        catch (Exception exception )
        exception.printStackTrace();
        throw new UnavailableException(exception.getMessage());
    }In the doPost method:
        if (conn == null)
        try
        WebAppsContext ctx = null;
        ctx = WebRequestUtil.validateContext(request, response);
        ctx = WebRequestUtil.createWebAppsContext(request, response);
        conn = ctx.getJDBCConnection();
        stmt = conn.createStatement();
        }Is this code correct to get a db connection? Pls. share thoughts/ideas/suggestions...
Thanks,