12.Java web--过滤器与监听器

1）过滤器

就是为请求与目标之间加一个或多个过滤器

自定义过滤器要实现Filter接口

下面是定义一个所有Servlet的请求中文不乱码

/**
 * 用于servlet输出中文乱码的过滤
 */
@WebFilter("/CharsetFilter")
public class CharsetFilter implements Filter {
   private String encode;
    public CharsetFilter() {
        // TODO Auto-generated constructor stub
    } 
    public void destroy() {
        // TODO Auto-generated method stub
    }
  
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
         if(encode!="") {
             response.setCharacterEncoding(encode);
             response.setContentType("text/html;charset="+encode);
         }
        //FilterChain的作用是进入下一步过滤或直接到达请求目标
        chain.doFilter(request, response);
    }
  
    public void init(FilterConfig fConfig) throws ServletException {
        //获取web.xml定义的参数
         encode=(String)fConfig.getInitParameter("encode");
    }
}

相关要在web.xml配置，与servlet配置差不多

<filter>
    <filter-name>CharsetFilter</filter-name>
    <filter-class>crm.CharsetFilter</filter-class>
    <!-- 定义一些初始参数 -->
    <init-param>
        <param-name>encode</param-name>
        <param-value>utf-8</param-value>
    </init-param>
</filter>
<filter-mapping>
    <filter-name>CharsetFilter</filter-name>
<!--     /*是通配符的写法，也可指定为某一个servlet或jsp页进行过滤
    如/index.jsp -->
    <url-pattern>/*</url-pattern>
</filter-mapping>

2）监听器

可以监听web状态变化，web容器产生的相应事件

1.Servlet上下监听

有两个接口：

ServletContextListener接口：监听ServletContext的创建与删除

ServletAttributeListener接口：监听ServletContext属性的增加、删除、修改（application范围）

例子，ServletAtrributeListener使用

public class MyServletAttributeListener implements ServletContextAttributeListener {
  
    public MyServletAttributeListener() {
        // TODO Auto-generated constructor stub
    }
//有新属性加入时触发
    public void attributeAdded(ServletContextAttributeEvent scae)  { 
         // TODO Auto-generated method stub
     ServletContext context=     scae.getServletContext();
      System.out.println("新增name:"+scae.getName()+"="+scae.getValue());
    }
 
      
    public void attributeRemoved(ServletContextAttributeEvent scae)  {  
         System.out.println("删除name:"+scae.getName()+"="+scae.getValue());
    }
  
    public void attributeReplaced(ServletContextAttributeEvent scae)  { 
         System.out.println("修改name:"+scae.getName()+"="+scae.getValue());
    } 
}

web.xml的配置

<listener>
  <listener-class>crm.MyServletAttributeListener</listener-class>
  </listener>

2.HTTP会话监听接口

HttpSessionListenner:监听会话的创建、销毁

HttpSessionActivationListener:监听HTTP会话的active\passivate

HttpBindingListener:当有对象加入移除session时触发，唯一一个不需要在web.xml配置，只要实例化即可启用

HttpSessionAttributeListener:设置session的Attribute时触发

3.Servlet请求监听

ServletRequestListener ：ServletRequest的创建与变更

ServletRequestAttributeListener ：ServletRequest的Attribute变化时

3）新增注释

像Servlet、Filter、Listener、WebInitParam等都要在web.xml配置，现在新增在类的实现方法，不需要再在web.xml配置

1. @WebServlet

只要在自定义的Servlet类上标注，如

@WebServlet(name="MyServlet",value= "/MyServlet", initParams= {@WebInitParam(name="weburl",value="http://www.x.com")})
public class MyServlet extends HttpServlet {
}

2. @WebFilter

3.WebListener

@WebListener("用于XXX")

4. @WebInitParam

5. @MultipartConfig

用于上传文件，用在Servlet类，且在@WebServlet注释之下

@WebServlet("/UpServlet")
@MultipartConfig(location="E:\\study\\java\\crm\\WebContent")
public class UpServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
        
    /**
     * @see HttpServlet#HttpServlet()
     */
    public UpServlet() {
        super();
        // TODO Auto-generated constructor stub
    }
 
    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        response.getWriter().append("Served at: ").append(request.getContextPath());
    }
 
    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
         PrintWriter out=response.getWriter();
         String path=getServletContext().getRealPath("/");//获取服务器地址
         Part p=request.getPart("file1");//获取用户选择的文件
         if(p.getContentType().contains("image")) {
             //仅处理图片的上传
             ApplicationPart ap=(ApplicationPart)p;
             String fnName=ap.getName();
             p.write( "E:\\study\\java\\crm\\WebContent\\upload\\aa.jpg");
             out.write("上传成功");
         }
    } 
}

要指定multipart/form-data

<form action="/crm/UpServlet" method="post" enctype="multipart/form-data">
     <input type="file" name="file1" id="file1" />
        <button type="submit">提交</button>
    </form>

6）异步处理

Servlet和Filter可以异步

@WebFilter(filterName="CharsetFilter",asyncSupported=true)
或者
<filter>
    <filter-name>CharsetFilter</filter-name>
    <filter-class>crm.CharsetFilter</filter-class>
    <async-supported>true</async-supported> 
  </filter>