10.1.1 Servlet filter provided by Application Server (built-in filter)

In Application Server, a servlet filter (built-in filter) is provided to use the following functionality:

Compressing the HTTP responses

To compress the HTTP responses for the HTTP requests, Application Server provides an HTTP response compression filter as the built-in filter.

The following table describes the types of built-in filters. Further, references of the functionality that you can use by embedding the built-in filter in a Web application are also described.

Table 10‒2: Types of built-in filters
Type of built-in filter	Description of functionality	Reference manual	Reference
HTTP response compression filter	This functionality compresses the HTTP responses to the HTTP requests for servlets, JSPs, and static contents, in the `gzip` format.	This manual	10.2

Note that with Servlet 3.0 or later, you can define a filter by using an API and not the web.xml file. However you cannot use an API to define a built-in filter.

The action of the built-in filter on HTTP requests and HTTP responses, the restrictions on the operation conditions of the built-in filter are explained below:

Organization of this subsection

(1) Action on the HTTP requests and HTTP responses
(2) Restriction on operation conditions

(1) Action on the HTTP requests and HTTP responses

The built-in filter acts on the request header and the request body of the HTTP requests sent from the client, and may delete, add, and change the information. In the same way, the built-in filter may also act on the response header and the response body of the HTTP responses sent from the server. The following table describes the action of the built-in filter on HTTP requests and HTTP responses:

Table 10‒3: Action of the built-in filter on HTTP requests and HTTP responses
Type of built-in filter	Action on the HTTP request	Action on the HTTP response
HTTP response compression filter	--	When the response body is compressed, `gzip` is specified in the Content-Encoding header. The response body is compressed in `gzip` format.

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(2) Restriction on operation conditions

When you use the user filter and the built-in filter simultaneously, there are restrictions on the order in which the built-in filter is invoked in the filter chain.

The following restrictions are explained for each built-in filter:

Restriction on the location

This is the restriction on the location (invocation order) of the built-in filter in the filter chain.
Restriction on operation conditions

This is a restriction on the operation conditions, such as the preconditions for operation of the built-in filter.
Restriction on the other servlet filters deployed before and after the built-in filter

This is a restriction with respect to servlet filters that are deployed before and after the built-in filter.

(a) Restrictions on an HTTP response compression filter

The following table describes the restrictions on the HTTP response compression filter:

Table 10‒4: Restrictions on the HTTP response compression filter
Type of restriction	Description
Restriction on the location	--
Restriction on operation conditions	--
Restriction on the other servlet filters deployed before and after the built-in filter	In the case of concurrent use of the HTTP response compression filter and servlet filter that changes the settings of the Content-Length header or the Content-Encoding header by using the `setHeader` method, `addHeader` method, `setIntHeader` method, or `addIntHeader` method of the `javax.servlet.http.HttpServletResponse` interface, you need to deploy the servlet filter after the HTTP response compression filter.

Legend:: --: Not applicable

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