The setting that specifies which servlet will be invoked for the URL requested by the client is called Servlet mapping. The Java servlet specification requires the servlet mapping to be coded in the DD (WEB-INF/web.xml).

On the other hand, the mapping defined by default in a Web container is called default mapping. In a Web container, the following mapping is defined by default:

Table 2-3 Default mapping of servlets or JSPs defined in a Web container

Note that for the servlet, web.xml must include mapping definition, and if web.xml is omitted, the default mapping of the servlet will not be enabled for the Web applications.

For the default mapping of the servlet, specify either enabled or disabled in the following parameter in the <configuration> tag of the logical J2EE server (j2ee-server) in the Easy Setup definition file. By default, the default mapping of the servlet is disabled.

webserver.container.servlet.default_mapping.enabled

For details on the Easy Setup definition file and the parameters to be specified, see 4.6 Easy Setup definition file in the uCosminexus Application Server Definition Reference Guide.

In a Web container, if the following tags are not set in the DD (WEB-INF/web.xml), use the following default values.

Table 2-4 Default values when tags in the DD (WEB-INF/web.xml) are not set

<welcome-file-list>
 <welcome-file>
 index.jsp
 </welcome-file>
 <welcome-file>
 index.html
 </welcome-file>
 <welcome-file>
 index.htm
 </welcome-file>
</welcome-file-list>

When the tags in above table are set in the DD (WEB-INF/web.xml) , the settings will be as follows:

• The default values are overwritten with the value set in <welcome-file-list> tag.
• The default values are overwritten with the value set in <session-timeout> tag.
• The default values are overwritten for each extension, by the settings for each extension defined in <mime-mapping> tag.

For details on the relationship between the extensions and the MIME types set by default in the mime-mapping tag of DD (WEB-INF/web.xml), see Appendix B.1 Correspondence Between Extensions and MIME Types in the uCosminexus Application Server Definition Reference Guide.

Create one servlet instance of the same class in each Web application. Also, create one servlet instance that inherits SingleThreadModel in each Web application in the same way as a general servlet.

However, if the same servlet and JSP are accessed by both default mapping and the mapping described in the DD, the instances are generated in the following manner.

Table 2-5 Generation of instances when the same servlet and JSP are accessed by both default mapping and the mapping described in the DD

Also, when multiple requests for a single servlet that inherits SingleThreadModel arrive concurrently in each Web application, control each thread so that the threads are executed one-by-one without overlapping.

The timing to execute the init method and service method of servlets differs according to the default mapping and the servlet mapping.

• When the servlets are accessed by default mapping:
  The init method and service method of servlets are executed as an extension of the filter processing mapped to the corresponding URL.
  
• When the servlets are accessed by servlet mapping:
  The init method is executed before the filter processing. The service method is executed as an extension of the filter processing mapped to the corresponding URL.
  

In the servlet buffer used for sending a response, only the number of request processing threads is maintained. When you use the setBufferSize method of javax.servlet.ServletResponse to change the buffer size, estimate the memory usage after considering that the memory of buffer size number of request processing threads is secured.

The query string includes a combination of one or more Name=Value after ? mark of URL.

With Application Server, if several = exist in the Name=Value part, the character string before the first = becomes the name and the character string after = becomes the value. For example, if the URL is http://host/examples?a=b=c, the string is analyzed as 'Value of name a is b=c'.