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過濾器書寫步驟
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1.創建類實現接口——DemoFilter implements Filter
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2.過濾任務要寫在doFilter方法中
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3.在web.xml中配置
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FilterDemo.java
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import java.io.IOException; import javax.servlet.*; public class FilterDemo implements Filter { @Override public void init(FilterConfig filterConfig) throws ServletException { System.out.println("----過濾器初始化----"); } @Override public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { System.out.println("FilterDemo01執行前！！！"); chain.doFilter(request, response); //讓目標資源執行，放行 System.out.println("FilterDemo01執行後！！！"); } @Override public void destroy() { System.out.println("----過濾器銷燬----"); } }
寫Servlet(也可以不寫，不寫的話就不用在web.xml中配置)
MyServlet.java
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class MyServlet extends HttpServlet{
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
PrintWriter out = resp.getWriter();
out.println("<html>" + "<body>" + "HelloWorld"
+ "</body>" + "</html>");
}
}
web.xml中的過濾器配置元素
1.聲明過濾器。2.將過濾器映射到你想過濾的Web資源。3.組織這些映射，創建過濾器調用序列。
（有servlet的寫法）
<filter>
<filter-name>FilterDemo01</filter-name>
<filter-class>FilterDemo</filter-class>
</filter>
<filter-mapping>
<filter-name>FilterDemo01</filter-name>
<servlet-name>MyServlet01</servlet-name>
</filter-mapping>
<servlet>
<servlet-name>MyServlet01</servlet-name>
<servlet-class>MyServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>MyServlet01</servlet-name>
<url-pattern>/hello.do</url-pattern>
</servlet-mapping>
（無servlet寫法）
<?xml version="1.0" encoding="ISO-8859-1"?>
<web-app xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
<filter>
<filter-name>FilterDemo01</filter-name>
<filter-class>FilterDemo</filter-class>
</filter>
<filter-mapping>
<filter-name>FilterDemo01</filter-name>
<url-pattern>/*</url-pattern>
</filter-mapping>
</web-app>
實驗
- 用過濾器實現 如果用戶訪問的不是登陸頁面，強行跳轉到登陸頁面
- 思路：
- request有一個方法getRequestURI()，可以得到用戶請求的URI
- String有一個方法indexOf(參數)，可以判斷參數是否在該String中。
- 綜上，登陸頁面的字符串，如果存在，過濾器就放行，讓用戶的請求繼續執行。否則，過濾器把該請求過濾掉，轉向登陸頁面。
FilterDemo.java(xml同上)
import java.io.IOException;
import javax.servlet.*;
import javax.servlet.http.*;
public class FilterDemo implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
System.out.println("----beginning----");
}
@Override
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req = (HttpServletRequest) request;
HttpServletResponse res = (HttpServletResponse) response;
System.out.println("before FilterDemo01");
String uri = req.getRequestURI();
int pos = uri.indexOf("login");
System.out.println("pose:" + pos);
if(pos>0){
chain.doFilter(request, response);
}else{
res.sendRedirect("login.html");
}
System.out.println("after FilterDemo01");
}
@Override
public void destroy() {
System.out.println("----destory----");
}
}
實驗過程中的問題
頁面一直報錯：此網頁包含重定向循環
看了tomcat窗口一直循環“before FilterDemo01”和“after FilterDemo01” ,一直在過濾器中沒有到達跳轉頁面
原因： int pos = uri.indexOf("hello"); pos取了“hello”的位置，但跳轉之後的也沒有，所以一直循環，
改成int pos = uri.indexOf("login"); 解決