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Oracle Sample Questions ›› Oracle Webserver

Technical Sample Questions

Oracle Sample Questions : Oracle WebServer

  1. How does one start and stop the Oracle Web Listener?

    Answer: V1:wlctlstart ‹ port_number ›eg.wlctlstart 8888

    wlctlstop ‹ port_number ›

    V2.0: wlctl2 start ‹ listener_name › eg.wlctl2 start admin

    wlctl2 stop ‹ listener_name ›

    V2.1: wlctl21 start ‹ listener_name › eg.wlctl21 start admin

    wlctl21 stop ‹ listener_name ›

  2. How does one program using the PL/SQL Web Agent?

    Answer: The Oracle Web Agent extends the Common Gateway Interface (CGI) to Oracle PL/SQL stored procedures.Programming is done in PL/SQL using the following set of packaged procedures:

    • HTP - Hypertext Procedures
    • HTF - Hypertext Functions
    • OWA_UTIL - Oracle Web Agent Utilities
    Example PL/SQL procedure:

    CREATE OR REPLACE PROCEDURE HelloWorld AS

    BEGIN

    htp.htitle('My first dynamic Web page');

    htp.print('Hello world');

    htp.line;

    END HelloWorld;

    /

    To run this example you would typically provide an URL like this to your Web Browser:

    http://your.host.name/oracle_connect_descriptor/owa/HelloWorld

  3. How to do multi-user updates using the Oracle WebServer?

    Answer: Because the Web is stateless, there is no way to lock data between a SELECT and an UPDATE initiated from a Web Browser.One workaround is to let the procedure that display the data for updating also store the data values in hidden fields
    .Eg:

    for c1 in (select rowid, a.* from emp a) loop

    htp.FormHidden('the_rowid', c1.rowid);

    htp.Print('Enter new Employee Name:');

    htp.FormHidden('old_ename', c1.ename);

    htp.FormText('new_ename', c1.ename);

    end loop;

    The update procedure can now compare the hidden values in the form with the current table values before allowing the update to continue.
    Eg:

    UPDATE emp SET ename = new_ename

    WHERE rowid = the_rowid

    AND ename = old_ename;

    if (SQL%ROWCOUNT = 0) then

    htp.print('Someone else changed this row, please re-query before updating.');

    else

    htp.print('1 row updated.');

    end if;

  4. Can one use Designer/2000 to generate Web applications?

    Answer: Yes.

    From Designer/2000 1.3W one can generate applications that can do Insert, Update and Delete operations.

  5. Should I access Oracle via the CGI interface or the WRB?

    Answer: The Oracle Web Request Broker (WRB) is faster and more scalable than the CGI-BIN program OWA, but can only be used with certain Web servers.CGI programs are spawned off each time a HTTP request is made to it while the WRB will only start new brokers if the workload increases.

    Note that the OWS-BIN OWA program's configuration parameters are stored in the SV*.CFG file while the WRB OWA is configured from SV*.APP.

  6. Can I store and retrieve images from an Oracle table?

    Answer: Sure you can, consider the following:

    • Oracle freely distributes a few unsupported CGI utilities that can do just that.Ask them for their IMGLOAD/ OWAI/ OWAUP utilities.
    • If you want to stream multiple IMAGES concurrently from a database table to Web Browsers look at OWA2.

  7. How does one use HTTP COOKIEs?

    Answer: Cookies allow any site to store information on a WEB Browser's hard disk (cookie.txt file).This information is sent back to the originating site whenever you access it again.

    Look at this code example:

    owa_util.mime_header ('text/html', FALSE);

    owa_cookie.send (cuid, xsession_id, sysdate);

    owa_util.http_header_close;

  8. I've lost the Web Server Administrator's password.What can I do?

    Answer: The Oracle WebServer Administrator's userid and password can be found in your $ORACLE_HOME/ows21/admin/svadmin.cfg file.The password is not encrypted!!!

  9. Can a Web page be refreshed/reloaded after a given interval?

    Answer: Yes,

  10. Why do I get "Requested URL was not found on this server"?

    Answer: Symptom:

    When attempting to access URLs such as:

    http://host:port/ows-bin/service/owa/proc

    the server responds with "Requested URL was not found on this server".

    Causes:

    • This is due to there not being a mapping in the service listener's Virtual Directory Mappings configuration, of the form: /home/oracle/ows2/bin/ CN /ows-bin/service/ so the "owa" program isn't found.
    • You're accessing a directory, /xxxx/, and the directory isn't readable by the Web Server process.
    • The Web Server is configured to not generate directory listings automatically, and there isn't an index.html file (or whatever you've picked as your index file name).

    Fix:

    • Create the virtual directory mapping, halt the listener, and restart it.
    • Check and fix the directory permissions.Note also the directory rescanning issue below.
    • Make sure that either the Web Server will create indices itself, or that there is a readable index file under the name you've specified.If altering the server configuration, halt and restart the server.

  11. Why do I get "Request failed.We were unable to process your request at this time.Please try again later"?

    Answer:

    Symptom: When attempting to access URLs such as:

    http://host:port/ows-bin/service/owa/proc

    the server responds with "Request failed.We were unable to process your request at this time.Please try again later."

    Cause:

    • The listener can't read the configuration file owa.cfg.
    • The listener is attempting to invoke the PL/SQL procedure named, but can't, for some reason.

    Fix:

    • Make sure that the file /home/oracle/owa2/admin/owa.cfg is readable by the user running the Web Server.
      • Check that the user for the listener has the permissions to invoke such functions: do "exec tw.ping" in sqlplus.There won't be any output, but it should say that it ran ok.If necessary, try reloading the stored procedures into the database.
      • Make sure that the names of the input fields in the form match up exactly with the names of the parameters in the script.There must be a one-to-one mapping.
      • If you've got multiple-value fields, such as SELECTs, make sure they're of the right type (defined in the OWA_UTIL package), and that there's an extra value supplied by a hidden field to force at least one value to be selected.
    • If all else fails, the procedure is probably raising an exception.Put OTHERS exception handlers around everything and call barf(errstr('procedure name')), or the moral equivalent on your system.
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