New servlet Features: annotations

Reference:

http://www.ibm.com/developerworks/cn/java/j-lo-servlet30/

Deployment profile for Servlet 3.0 The top-level label for Web. XML <web-app> has a Metadata-complete property that specifies whether the current deployment profile is complete. If set to true, the container will only rely on the deployment profile at deployment time, ignoring all annotations (also skipping web-fragment.xml scans, i.e. disabling pluggable support, see the following for pluggable support); If you do not configure this property, or set it to False, annotation support (and pluggable support) is enabled.

@WebServlet

@WebServlet is used to declare a class as a servlet, which will be handled by the container at deployment time, and the container will deploy the appropriate class as a servlet based on the specific property configuration. The note has some of the common properties given in the following table (all of which are optional), but Vlaue or urlpatterns are usually required and cannot coexist, and if specified at the same time, the value of value is usually ignored. Name is used to map to the servlet by name when using filters:

Table 1. @WebServlet List of main attributes

Property name	type	Description
Name	String	Specifies the Name property of the Servlet, equivalent to <servlet-name>. If not explicitly specified, the value of the Servlet is the fully qualified name of the class.
Value	String[]	This property is equivalent to the Urlpatterns property. Two attributes cannot be used at the same time.
Urlpatterns	String[]	Specifies the URL-matching pattern for a set of Servlets. Equivalent to <url-pattern> tag.
Loadonstartup	Int	Specifies the order in which the Servlet is loaded, equivalent to the <load-on-startup> tag.
InitParams	Webinitparam[]	Specifies a set of Servlet initialization parameters, equivalent to the <init-param> tag.
asyncsupported	Boolean	Declares whether the Servlet supports asynchronous operation patterns, equivalent to <async-supported> tags.
Description	String	The Servlet's descriptive information is equivalent to the <description> tag.
DisplayName	String	The display name of the Servlet, usually used in conjunction with the tool, is equivalent to the <display-name> tag.

The following is a simple example:

True=-1, name = "Simpleservlet", DisplayName = "ss"= {@WebInitParam (name = "Username", value = "to M "publicclassextends httpservlet{...}

With this configuration, you do not have to configure the appropriate <servlet> and <servlet-mapping> elements in Web. XML, and the container publishes the class as a servlet at deployment time, based on the specified properties. Its equivalent web. XML configuration form is as follows:

<servlet>    <Display-name>Ss</Display-name>    <Servlet-name>Simpleservlet</Servlet-name>    <Servlet-class>Footmark.servlet.SimpleServlet</Servlet-class>    <Load-on-startup>-1</Load-on-startup>    <async-supported>True</async-supported>    <Init-param>        <Param-name>Username</Param-name>        <Param-value>Tom</Param-value>    </Init-param></servlet><servlet-mapping>    <Servlet-name>Simpleservlet</Servlet-name>    <Url-pattern>/simple</Url-pattern></servlet-mapping>

@WebInitParam

This annotation is usually not used alone, but is used in conjunction with @WebServlet or @WebFilter. Its purpose is to specify initialization parameters for the Servlet or filter, which is equivalent to the <init-param> sub-tags of <servlet> and <filter> in Web. Xml. @WebInitParam have some common properties that are given in the following table:

Table 2. Common Properties for @WebInitParam

Property name	type	is optional	Description
Name	String	Whether	Specifies the name of the parameter, equivalent to <param-name>.
Value	String	Whether	Specifies the value of the parameter, equivalent to <param-value>.
Description	String	Is	A description of the parameter is equivalent to <description>.

The following is a simple example:

@WebFilter (Servletnames = {"Simpleservlet"},filtername= "Simplefilter"Publicclass  implements filter{...}

With this configuration, you do not have to configure the appropriate <filter> and <filter-mapping> elements in Web. XML, and the container publishes the class as a filter at deployment time, based on the specified properties. Its equivalent in Web. XML is configured in the following form:

<Filter>     <Filter-name>Simplefilter</Filter-name>     <Filter-class>Xxx</Filter-class> </Filter> <filter-mapping>     <Filter-name>Simplefilter</Filter-name>     <Servlet-name>Simpleservlet</Servlet-name> </filter-mapping>

@WebFilter

@WebFilter is used to declare a class as a filter that will be handled by the container at deployment time, and the container will deploy the appropriate class as a filter based on the specific property configuration. The note has some of the common properties given in the following table (all the properties below are optional, but value, Urlpatterns, Servletnames must contain at least one, and value and urlpatterns cannot coexist, and if specified at the same time, it is generally ignored Value):

Table 3. Common Properties for @WebFilter

Property name	type	Description
FilterName	String	Specify the Name property of the filter, equivalent to <filter-name>
Value	String[]	This property is equivalent to the Urlpatterns property. But both should not be used at the same time.
Urlpatterns	String[]	Specifies the URL-matching pattern for a set of filters. Equivalent to <url-pattern> tag.
Servletnames	String[]	Specifies which servlets the filter will be applied to. The value is the value of the name attribute in the @WebServlet, or the value of <servlet-name> in Web. Xml.
Dispatchertypes	Dispatchertype	Specifies the forwarding mode of the filter. Specific values include: ASYNC, ERROR, FORWARD, INCLUDE, REQUEST.
InitParams	Webinitparam[]	Specifies a set of filter initialization parameters, equivalent to the <init-param> tag.
asyncsupported	Boolean	Declares whether the filter supports asynchronous operation mode, equivalent to the <async-supported> tag.
Description	String	The description information of the filter is equivalent to the <description> tag.
DisplayName	String	The filter's display name, usually used with the tool, is equivalent to the <display-name> tag.

The following is a simple example:

@WebFilter (Servletnames = {"Simpleservlet"},filtername= "Simplefilter"publicclass  Implements filter{...}

@WebListener

This annotation is used to declare a class as a listener, and the class that is @WebListener labeled must implement at least one of the following interfaces:

• Servletcontextlistener
• Servletcontextattributelistener
• Servletrequestlistener
• Servletrequestattributelistener
• Httpsessionlistener
• Httpsessionattributelistener

This annotation is very simple to use and its properties are as follows:

Table 4. Common Properties for @WebListener

Property name	type	is optional	Description
Value	String	Is	The description information for the listener.

A simple example is as follows:

@WebListener ("This was only a demo listener") public class SimpleListener implements servletcontextlistener{...}

In this case, you do not need to configure the <listener> tag in Web. Xml. It is equivalent to the configuration form in Web. Xml as follows:

<listener>     <listener-class>footmark.servlet.SimpleListener</listener-class> </ Listener>

@MultipartConfig

This note is primarily intended to assist in the support provided by HttpServletRequest in Servlet 3.0 for uploading files. The note is labeled above the servlet to indicate that the MIME type of the request that the servlet wishes to process is multipart/form-data. In addition, it provides several properties for simplifying the processing of uploaded files. Specific as follows:

Table 5. Common Properties for @MultipartConfig

Property name	type	is optional	Description
Filesizethreshold	Int	Is	When the amount of data is greater than this value, the content is written to the file.
Location	String	Is	Store the generated file address.
MaxFileSize	Long	Is	Maximum number of files allowed to upload. The default value is-1, which means there is no limit.
Maxrequestsize	Long	Is	The maximum number of requests for the Multipart/form-data, the default value is-1, which means there is no limit.

New servlet Features: annotations