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| <meta name="author" value="Jon S. Stevens"> |
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| <title>Velocity - You make the decision - Hosting</title> |
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| <p><strong>About</strong></p> |
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| <li> <a href="../index.html">Overview</a> |
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| <a name="Hosting"><strong>Hosting</strong></a> |
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| <tr><td> |
| <blockquote> |
| <p> |
| JSP is great for hosted environments (ie: shared development |
| environments, ISP's and large companies) where many different kinds of |
| people are putting pages on the servlet engine may not know much more |
| than HTML. Part of the reason it is so nice is that with the HTML'ish |
| syntax JSP is so easy to learn! |
| </p> |
| <p> |
| However, if one really looks at that statement in more detail it becomes |
| apparent that this might not be such a good thing. Consider the |
| following snippet of Java code: |
| </p> |
| <div align="left"> |
| <table cellspacing="4" cellpadding="0" border="0"> |
| <tr> |
| <td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| <td bgcolor="#023264" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| <td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| </tr> |
| <tr> |
| <td bgcolor="#023264" width="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| <td bgcolor="#ffffff"><pre> |
| Hashtable strings = new Hashtable(); |
| int i=0; |
| while (true) |
| { |
| strings.put ("dead"+i, new StringBuffer(999999)); |
| } |
| </pre></td> |
| <td bgcolor="#023264" width="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| </tr> |
| <tr> |
| <td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| <td bgcolor="#023264" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| <td bgcolor="#023264" width="1" height="1"><img src="/images/void.gif" width="1" height="1" vspace="0" hspace="0" border="0"/></td> |
| </tr> |
| </table> |
| </div> |
| <p> |
| What this does is that it creates a Hashtable and then goes into a tight |
| loop. At the same time, it creates a new StringBuffer object that has a |
| default size of 999999. Therefore, creating what amounts to a memory |
| leak in the Java Virtual Machine (which all of the hosted applications |
| share). |
| </p> |
| <p> |
| As soon as all of the memory is gone, every single hosted application |
| will start to receive the dreaded "OutOfMemoryError". The reason why |
| this is so bad has already been explained <a href="./ymtd-error-handling.html">earlier</a>. Essentially JSP pages |
| themselves cannot catch OOME errors and the entire servlet engine will |
| suddenly become useless, all because of what amounts to a few lines of |
| badly written Java code. |
| </p> |
| <p> |
| Remember, it is a bad idea to put Java code into a JSP page. Tell that |
| to the 14 year old kid who is being hosted on your ISP's servlet engine |
| who really does not care that others might be affected by these actions. |
| </p> |
| <p> |
| Velocity does not have this issue because there is no while loop in the |
| Velocity Template Language. The only looping construct in Velocity is a |
| #foreach and that loops over an array that has a finite amount of |
| elements. It is also possible to disable the #foreach directive and |
| limit the amount of recursive nesting that is possible. Note: it is |
| possible to modify Velocity to add a #while directive to the template |
| language. |
| </p> |
| <p> |
| There is nothing in JSP or Struts that prevents people from embedding |
| Java code in the page. |
| </p> |
| <p> |
| You make the decision. |
| </p> |
| <p> |
| <strong>[ <a href="ymtd-implementation.html">Implementation</a> <- Previous | |
| Next -> <a href="./ymtd-conclusion.html">Conclusion</a> ] |
| </strong></p> |
| </blockquote> |
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