Servlet-注释 - 芒果文档

📌 相关文章

📜 Servlet-注释

📅 最后修改于: 2020-11-12 05:47:44 🧑 作者: Mango

到目前为止，您已经了解了Servlet如何使用部署描述符(web.xml文件)将应用程序部署到Web服务器中。 Servlet API 3.0引入了一个名为javax.servlet.annotation的新程序包。它提供了可用于对Servlet类进行注释的注释类型。如果使用批注，则不需要部署描述符(web.xml)。但是您应该使用tomcat7或任何更高版本的tomcat。

注释可以替换Web部署描述符文件(web.xml)中的等效XML配置，例如Servlet声明和Servlet映射。 Servlet容器将在部署时处理带注释的类。

Servlet 3.0中引入的注释类型为-

Sr.No.	Annotation & Description
1	@WebServlet To declare a servlet.
2	@WebInitParam To specify an initialization parameter.
3	@WebFilter To declare a servlet filter.
4	@WebListener To declare a WebListener
5	@HandlesTypes To declare the class types that a ServletContainerInitializer can handle.
6	@HttpConstraint This annotation is used within the ServletSecurity annotation to represent the security constraints to be applied to all HTTP protocol methods for which a corresponding HttpMethodConstraint element does NOT occur within the ServletSecurity annotation.
7	@HttpMethodConstraint This annotation is used within the ServletSecurity annotation to represent security constraints on specific HTTP protocol messages.
8	@MultipartConfig Annotation that may be specified on a Servlet class, indicating that instances of the Servlet expect requests that conform to the multipart/form-data MIME type.
9	@ServletSecurity This annotation is used on a Servlet implementation class to specify security constraints to be enforced by a Servlet container on HTTP protocol messages.

在这里，我们已经详细讨论了一些注释。

@WebServlet

@WebServlet用于通过容器声明Servlet的配置。下表包含用于WebServlet批注的属性的列表。

Sr.No.	Attribute & Description
1	String name Name of the Servlet
2	String[] value Array of URL patterns
3	String[] urlPatterns Array of URL patterns to which this Filter applies
4	Int loadOnStartup The integer value gives you the startup ordering hint
5	WebInitParam[] initParams Array of initialization parameters for this Servlet
6	Boolean asyncSupported Asynchronous operation supported by this Servlet
7	String smallIcon Small icon for this Servlet, if present
8	String largeIcon Large icon for this Servlet, if present
9	String description Description of this Servlet, if present
10	String displayName Display name of this Servlet, if present

注释的value或urlPattern属性中必须声明至少一个URL模式，但不能两者都声明。

当URL模式是唯一设置的属性时，建议使用value属性，否则应使用urlPattern属性。

例

以下示例描述了如何使用@WebServlet批注。这是一个简单的servlet，显示文本Hello Servlet 。

import java.io.IOException; 
import java.io.PrintWriter; 
import javax.servlet.ServletException; 
import javax.servlet.annotation.WebInitParam; 
import javax.servlet.annotation.WebServlet; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse; 
@WebServlet(value = "/Simple") 
public class Simple extends HttpServlet {

   private static final long serialVersionUID = 1L; 

   protected void doGet(HttpServletRequest request, HttpServletResponse response)  
      throws ServletException, IOException { 
   
      response.setContentType("text/html");   
      PrintWriter out = response.getWriter();   
      out.print("");   
      out.print("Hello Servlet");   
      out.print("");         
   }   
}

以通常的方式编译Simple.java并将类文件放入 / webapps / ROOT / WEB-INF / classes中。

现在，尝试通过运行http：// localhost：8080 / Simple来调用任何servlet。您将在网页上看到以下输出。

Hello servlet

@WebInitParam

@WebInitParam批注用于为Servlet或Filter指定初始化参数。在WebFilter或WebSevlet批注中使用它。下表包含用于WebInitParam批注的属性列表。

Sr.No.	Attribute & Description
1	String name Name of the initialization parameter
2	String value Value of the initialization parameter
3	String description Description of the initialization parameter

Sr.No.

Attribute & Description

String name

Name of the initialization parameter

String value

Value of the initialization parameter

String description

Description of the initialization parameter

例

以下示例描述了如何将@WeInitParam注释与@WebServlet注释一起使用。这是一个简单的servlet，显示文本Hello Servlet和字符串值Hello World！从init参数中获取。

import java.io.IOException; 
import java.io.PrintWriter; 
import javax.servlet.ServletException; 
import javax.servlet.annotation.WebInitParam; 
import javax.servlet.annotation.WebServlet; 
import javax.servlet.http.HttpServlet; 
import javax.servlet.http.HttpServletRequest; 
import javax.servlet.http.HttpServletResponse;

@WebServlet(value = "/Simple", initParams = { 
   @WebInitParam(name = "foo", value = "Hello "), 
   @WebInitParam(name = "bar", value = " World!") 
}) 
public class Simple extends HttpServlet {

   private static final long serialVersionUID = 1L; 

   protected void doGet(HttpServletRequest request, HttpServletResponse response)
      throws ServletException, IOException {   
      
      response.setContentType("text/html");   
      PrintWriter out = response.getWriter();   
      out.print("");   
      out.print("Hello Servlet");   
      out.println(getInitParameter("foo")); 
      out.println(getInitParameter("bar")); 
      out.print("");         
   }   
}

以通常的方式编译Simple.java并将类文件放入; / webapps / ROOT / WEB-INF / classes。

现在，尝试通过运行http：// localhost：8080 / Simple来调用任何servlet。您将在网页上看到以下输出。

Hello Servlet

Hello World!

@Webfilter

这是用于声明servlet过滤器的注释。容器在部署时对其进行处理，并将相应的过滤器应用于指定的URL模式，Servlet和调度程序类型。

@WebFilter批注定义了Web应用程序中的过滤器。该注释在类中指定，并且包含有关要声明的过滤器的元数据。带注释的过滤器必须指定至少一个URL模式。下表列出了用于WebFilter批注的属性。

Sr.No.	Attribute & Description
1	String filterName Name of the filter
2	String[] urlPatterns Provides array of values or urlPatterns to which the filter applies
3	DispatcherType[] dispatcherTypes Specifies the types of dispatcher (Request/Response) to which the filter applies
4	String[] servletNames Provides an array of servlet names
5	String displayName Name of the filter
6	String description Description of the filter
7	WebInitParam[] initParams Array of initialization parameters for this filter
8	Boolean asyncSupported Asynchronous operation supported by this filter
9	String smallIcon Small icon for this filter, if present
10	String largeIcon Large icon for this filter, if present

例

下面的示例描述如何使用@WebFilter批注。这是一个简单的LogFilter，可在控制台上显示Init-param test-param的值和当前时间时间戳。这意味着，过滤器的工作方式类似于请求和响应之间的接口层。在这里，我们将“ / *”用于urlPattern。这意味着，此过滤器适用于所有servlet。

import java.io.IOException; 
import javax.servlet.annotation.WebFilter; 
import javax.servlet.annotation.WebInitParam; 
import javax.servlet.*; 
import java.util.*;  

// Implements Filter class

@WebFilter(urlPatterns = {"/*"}, initParams = { 
   @WebInitParam(name = "test-param", value = "Initialization Paramter")}) 
public class LogFilter implements Filter {
   
   public void init(FilterConfig config) throws ServletException { 
      // Get init parameter  
      String testParam = config.getInitParameter("test-param");
            
      //Print the init parameter  
      System.out.println("Test Param: " + testParam);  
   } 

   public void doFilter(ServletRequest request, ServletResponse response,
      FilterChain chain) throws IOException, ServletException { 
      
      // Log the current timestamp. 
      System.out.println("Time " + new Date().toString());  
         
      // Pass request back down the filter chain 
      chain.doFilter(request,response); 
   }

   public void destroy( ) {
      /* Called before the Filter instance is removed  
      from service by the web container*/ 
   } 
}

以通常的方式编译Simple.java并将类文件放入 / webapps / ROOT / WEB-INF / classes中。

现在，尝试通过运行http：// localhost：8080 / Simple来调用任何servlet。您将在网页上看到以下输出。

Hello Servlet
  
Hello World!

现在，打开servlet控制台。在这里，您将找到init参数testparam的值，当前时间戳以及servlet通知消息。