Java Servlet Exceptions

What about Servlets and Exceptions?

  • Exception can be handle in different ways .

Exception in the code

  • Some exceptions can be handled by adding try-catch blocks into the code.
    ...
    String num = req.getParameter("number");
    try {
      Integer i = new Integer(num);
      writer.println("You entered the number " + i.intValue());
    } catch (java.lang.NumberFormatException e) {
      writer.println(" Number is not convertable: " + num);
    }
    ...

Specify Exception in the Deployment Descriptor (web.xml)

  • Example - specify an error page for a Java exception.
    ...
    <error-page>
      <exception-type>java.lang.NumberFormatException</exception-type>
      <location>/WEB-INF/BadNumber.html</location>
    </error-page>
    ...
  • For any java.lang.NumberFormatException a new page will be returned to the client (browser).
  • Example - specify an error page for an HTTP protocal error.
    ...
    <error-page>
      <error-code>404</error-code>
      <location>/WEB-INF/NoSuchPage.html</location>
    </error-page>
    ...

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