@ WebServlet annotations (Servlet annotations)

@WebServlet annotation

Article Directory

• @WebServlet annotation
• Foreword
• First, the attributes of the @WebServlet annotation
• Second, the use of @WebServlet annotation
• • 1. Enable annotation support
  • 2. Use @WebServlet annotation
• The difference between @WebServlet annotation and web.xml

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Foreword

In Servlet, the role of web.xml is very important. It can centrally manage the configuration of all Servlets. However, if the number of Servelts in the project is large, the configuration of web.xml will become very verbose.In this case, Annotation is a better choice.

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Tips: The following is the text of this article, and the following cases are for reference

First, the attributes of the @WebServlet annotation

Second, the use of @WebServlet annotation

1. Enable annotation support

There is an attribute in the top-level tag of

web.xml: metadata-complete, which is used to specify whether the current web.xml is complete.If this property is set to true, the container will only rely on web.xml when deploying, ignoring all annotations.If this property is not configured, or set to false, annotation support is enabled.
Since the default value of the metadata-complete attribute is false, that is, Servlet annotation support is enabled by default, so by default, when using this annotation, there is no need to create a web.xml file.

2. Use @WebServlet annotation

@WebServlet is a class-level annotation, which is annotated on the class that inherits HttpServlet.The common way of writing is to write the relative request path (ie value) of the servlet directly in the annotation,
@WebServlet(urlPatterns = “/MyServlet”).
@WebServlet(“/MyServlet”) omits the urlPatterns attribute name
If multiple attributes need to be set in @WebServlet, they must be separated by commas.
Created by implementing Serlvet interface or inheriting GenericServletServlet classes cannot be annotated with @WebServlet.
Use the servlet class configured with the @WebServlet annotation, do not configure the servlet related properties again in the web.xml file.If both web.xml and @WebServlet are used to configure the same servlet class, the value in web.xml cannot be the same as the value of name in the annotation, otherwise the container will ignore the configuration in the annotation.

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The difference between the @WebServlet annotation and web.xml

Use web.xml or @WebServlet annotation to configure Servlet
@WebServlet annotation to configure Servlet
Advantages: @WebServlet can be used directly in the Servlet class, with less code and simple configuration.Each class only focuses on its own business logic and does not interfere with other servlet classes, which is suitable for multiple people to develop at the same time.
Disadvantage: When there are many servlets, the configuration of each servlet is distributed in its own class, which is not easy to find and modify.

Web.xml configuration file configuration Servlet
Advantages: Centralized management of Servlet configuration, easy to find and modify.
Disadvantages: The code is cumbersome, not readable, and not easy to understand.