Servlet过滤器(非法字符审核案例)
1、过滤器
(1)什么是过滤器servlet规范当中定义的一种特殊的组件，用来拦截容器的调用过程并进行相应的处理。
(2)如何写一个过滤器
step1,写一个java类，实现Filter接口。
step2,在doFilter方法，编写拦截处理逻辑。
step3,在web.xml文件里面，配置过滤器(让容器针对特定的地址进行拦截处理)。
(3)过滤器的优先级
当有多个过滤器都满足过滤的条件，容器会按照<filter-mapping>的先后顺序来调用相应的过滤器。
(4)初始化参数
step1,在web.xml文件中添加
<init-param>
<param-name>length</param-name>
<param-value>10</param-value>
</init-param>
step2,使用String FilterConfig.getInitParameter("length");
(5)过滤器的优点
1)可以实现代码的"可插拔性"(即增加或者减少某个功能模块，不会影响到程序的正常运行)。
2)可以将多个模块相同的处理逻辑集中写在过滤器里面，方便代码的维护。
2、案例：非法字符审核
comment_form.jsp：
<%@page pageEncoding="utf-8" contentType="text/html;charset=utf-8" %> <html> <head></head> <body style="font-size:30px;"> <form action="comment" method="post"> 请输入你的评论:<input name="content"/> <input type="submit" value="发表"/> </form> </body> </html>
配置web.xml:
<!-- 配置过滤器 -->
<filter>
<filter-name>filter1</filter-name>
<filter-class>web.CommentFilter1</filter-class>
</filter>
<filter>
<filter-name>filter2</filter-name>
<filter-class>web.CommentFilter2</filter-class>
<!-- 初始化参数 -->
<init-param>
<param-name>length</param-name>
<param-value>5</param-value>
</init-param>
</filter>
<!--
<filter-mapping>
<filter-name>filter2</filter-name>
<url-pattern>/comment</url-pattern>
</filter-mapping>
-->
<filter-mapping>
<filter-name>filter1</filter-name>
<url-pattern>/comment</url-pattern>
</filter-mapping>
<servlet>
<servlet-name>CommentServlet</servlet-name>
<servlet-class>web.CommentServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>CommentServlet</servlet-name>
<url-pattern>/comment</url-pattern>
</servlet-mapping>
CommentServlet.java：
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CommentServlet extends HttpServlet {
public void service(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException {
System.out.println("commentServlet's service begin...");
request.setCharacterEncoding("utf-8");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
String content = request.getParameter("content");
out.println("你的评论内容是:" + content);
out.close();
System.out.println("commentServlet's service end.");
}
}
CommentFilter1.java：
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CommentFilter1 implements Filter{
public CommentFilter1(){
System.out.println("filter1's constructor...");
}
/*
* 容器在销毁过滤器实例之前，会调用destroy方法，该方法只会执行一次。
*/
public void destroy() {
System.out.println("filter1's destroy...");
}
/*
* 容器会调用doFilter方法来处理请求。
* 容器会将request,response作为参数传递给doFilter方法，如果调用了FilterChain对象的doFilter方法，
* 容器会调用后续的过滤器或者servlet；否则，返回。
*/
public void doFilter(ServletRequest arg0,
ServletResponse arg1, FilterChain arg2)
throws IOException, ServletException {
System.out.println("filter1's doFilter begin...");
HttpServletRequest request =
(HttpServletRequest)arg0;
HttpServletResponse response =
(HttpServletResponse)arg1;
request.setCharacterEncoding("utf-8");
String content = request.getParameter("content");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
if(content.indexOf("dog") != -1){
out.println("非法评论");
}else{
//调用后续的过滤器或者servlet
arg2.doFilter(arg0, arg1);
}
System.out.println("filter1's doFilter end.");
}
/*
* 容器在启动之后，会立即创建过滤器实例。接下来，会调用init方法完成初始化。
* FilterConfig对象由容器创建，其作用是访问过滤器的初始化参数<init-param>。
* init方法只会调用一次。
*/
public void init(FilterConfig arg0) throws ServletException {
System.out.println("filter's init...");
}
}
CommentFilter2.java：
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class CommentFilter2 implements Filter{
private FilterConfig config;
public void destroy() {
}
public void doFilter(ServletRequest arg0,
ServletResponse arg1, FilterChain arg2) throws IOException, ServletException {
//日志工具(log4j)
System.out.println("Filter2's doFilter begin...");
HttpServletRequest request =
(HttpServletRequest)arg0;
HttpServletResponse response =
(HttpServletResponse)arg1;
request.setCharacterEncoding("utf-8");
String content = request.getParameter("content");
response.setContentType("text/html;charset=utf-8");
PrintWriter out = response.getWriter();
int length = Integer.parseInt(
config.getInitParameter("length"));
if(content.length() > length){
out.println("长度非法");
}else{
arg2.doFilter(arg0, arg1);
}
System.out.println("Filter2's doFilter end.");
}
public void init(FilterConfig arg0) throws ServletException {
config = arg0;
}
}