Often asked: How Does Servlet Filter Work?

A Servlet Filter in a Java Web Application When a HTTP request arrives at your web application which the filter intercepts, the filter can inspect the request URI, the request parameters and the request headers, and based on that decide if it wants to block or forward the request to the target servlet, JSP etc.

What is filter in servlet?

A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both. Filters perform filtering in the doFilter method.

Why do we need a servlet filter?

Why do we have Servlet Filter? Servlet Filters are pluggable java components that we can use to intercept and process requests before they are sent to servlets and response after servlet code is finished and before container sends the response back to the client.

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What is servlet filter and its advantages?

It is mainly used to perform filtering tasks such as conversion, logging, compression, encryption and decryption, input validation etc. The servlet filter is pluggable, i.e. its entry is defined in the web. xml file, filter will be removed automatically and we don’t need to change the servlet.

How we can filter request and response in servlet?

The filtering API is defined by the Filter, FilterChain, and FilterConfig interfaces in the javax. servlet package. You define a filter by implementing the Filter interface. The most important method in this interface is doFilter, which is passed request, response, and filter chain objects.

What is the difference between servlet and filter?

Filter provides functionality which can be “attached” to any web resource. Servlet used for performing action which needs for particular request as user login, get response based on user role, interacts with database for getting data, business logic execution, and more.

Can a filter be attached to one or more servlets?

Filters typically do not themselves create responses, but instead provide universal functions that can be “attached” to any type of servlet or JSP page.

Why listeners are used in servlets?

Using the feature of Listener introduced in Servlet, we can make a web application which responds to events taking place in a web application. These events can be of request, session or application level scope. On the basis of these different types of events, there are several Listener interfaces defined under javax.

What is JSP page in Java?

JavaServer Pages (JSP) is a Java standard technology that enables you to write dynamic, data-driven pages for your Java web applications. JSP is built on top of the Java Servlet specification. The two technologies typically work together, especially in older Java web applications.

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When init () method of filter gets called?

Q 20 – When init method of filter gets called? A – The init method is called by the web container to indicate to a filter that it is being placed into service.

What is JSP life cycle?

A JSP life cycle is defined as the process from its creation till the destruction. This is similar to a servlet life cycle with an additional step which is required to compile a JSP into servlet.

What is an HTTP filter?

HTTP filters help to limit the amount of output data. A filter can be created for a particular application, protocol and/or IP address. RegExp rules for a Request Header may be also applied.

Can we have multiple filters in web xml?

Multiple filters associated with a web resource are executed in the order of <filter-mapping> tag, which is specified in the deployment descriptor file(web. xml).

Which filter performs the work of writing the appropriate HTTP headers to the response?

The order of the filter (from IOrderedFilter). The ResponseCacheAttribute is used to configure and create (via IFilterFactory) a ResponseCacheFilter, which performs the work of writing the appropriate HTTP headers to the response.

How do I add a filter to my Web application?

To configure a filter:

  1. Open the web. xml deployment descriptor in a text editor or use the Administration Console.
  2. Add a filter declaration.
  3. Specify one or more initialization attributes inside a <filter> element.
  4. Add filter mappings.
  5. To create a chain of filters, specify multiple filter mappings.

What does Chain doFilter do?

doFilter. Causes the next filter in the chain to be invoked, or if the calling filter is the last filter in the chain, causes the resource at the end of the chain to be invoked. Parameters: request – the request to pass along the chain.

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