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| <!DOCTYPE document [ |
| <!ENTITY project SYSTEM "project.xml"> |
| ]> |
| <document url="aio.html"> |
| |
| &project; |
| |
| <properties> |
| <title>Advanced IO and Tomcat</title> |
| <author>Remy Maucherat</author> |
| </properties> |
| |
| <body> |
| |
| <section name="Table of Contents"> |
| <toc/> |
| </section> |
| |
| <section name="Introduction"> |
| |
| <p> |
| <b>IMPORTANT NOTE: Usage of these features requires using the |
| HTTP connectors. The AJP connectors do not support them.</b> |
| </p> |
| |
| </section> |
| |
| <section name="Asynchronous writes"> |
| |
| <p> |
| When using HTTP connectors (based on APR or NIO/NIO2), |
| Tomcat supports using sendfile to send large static files. |
| These writes, as soon as the system load increases, will be performed |
| asynchronously in the most efficient way. Instead of sending a large response using |
| blocking writes, it is possible to write content to a static file, and write it |
| using a sendfile code. A caching valve could take advantage of this to cache the |
| response data in a file rather than store it in memory. Sendfile support is |
| available if the request attribute <code>org.apache.tomcat.sendfile.support</code> |
| is set to <code>Boolean.TRUE</code>. |
| </p> |
| |
| <p> |
| Any servlet can instruct Tomcat to perform a sendfile call by setting the appropriate |
| request attributes. It is also necessary to correctly set the content length |
| for the response. When using sendfile, it is best to ensure that neither the |
| request or response have been wrapped, since as the response body will be sent later |
| by the connector itself, it cannot be filtered. Other than setting the 3 needed |
| request attributes, the servlet should not send any response data, but it may use |
| any method which will result in modifying the response header (like setting cookies). |
| </p> |
| |
| <ul> |
| <li><code>org.apache.tomcat.sendfile.filename</code>: Canonical filename of the file which will be sent as |
| a String</li> |
| <li><code>org.apache.tomcat.sendfile.start</code>: Start offset as a Long</li> |
| <li><code>org.apache.tomcat.sendfile.end</code>: End offset as a Long</li> |
| </ul> |
| <p> |
| In addition to setting these parameters it is necessary to set the content-length header. |
| Tomcat will not do that for you, since you may have already written data to the output stream. |
| </p> |
| |
| <p> |
| Note that the use of sendfile will disable any compression that Tomcat may |
| otherwise have performed on the response. |
| </p> |
| |
| </section> |
| |
| </body> |
| </document> |