过滤器
生命周期：初始化 -----过滤-------销毁
作用：过滤url ，特定字符
创建方式：实现一个接口继承Filter
package com.baidu.filter;
import java.io.IOException;
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;
public class Demo01 implements Filter {
public void destroy() {
System.out.println("过滤销毁");
}
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {
System.out.println("请求过滤");
MyHttpServletRequest msr=new MyHttpServletRequest((HttpServletRequest)request);
chain.doFilter(msr, response);
System.out.println("响应过滤");
}
/**
* @see Filter#init(FilterConfig)
*/
public void init(FilterConfig fConfig) throws ServletException {
System.out.println("过滤器初始化");
}
}
配置过滤器（web.xml）
和配置servlet相似。
<filter>
<filter-name>Demo01</filter-name>
<filter-class>com.baidu.filter.Demo01</filter-class>
</filter>
<filter-mapping>
<filter-name>Demo01</filter-name>
<url-pattern>/*</url-pattern>//可以设置经过过滤器的url /*表示项目下的所有路径都得经过过滤器
</filter-mapping>
过滤器在web中的位置
浏览器 < ------------ > 过滤器 < ------------ > 服务器
注意事项
1.配置文件中会配置Filter过滤器的位置只要符合其位置就会经过过滤器
2.请求完成以后响应动作也会经过过滤器
使用过滤器来修改编码格式，这样就不需要用每个servlet中去修改编码格式了
（使用的装饰者设计模式来实现）
package com.baidu.filter;
import java.io.UnsupportedEncodingException;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;
public class MyHttpServletRequest extends HttpServletRequestWrapper {
private HttpServletRequest request;
public MyHttpServletRequest(HttpServletRequest request) {
super(request);
this.request=request;
}
@Override
public String getParameter(String name) {
//判断提交方式（get/post）
String method = request.getMethod();
if ("Get".equalsIgnoreCase(method)) {
String value = super.getParameter(name);
try {
value = new String(value.getBytes("ISO-8859-1"),"UTF-8");
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return value;
}
if ("post".equalsIgnoreCase(method)) {
try {
System.out.println(request.getCharacterEncoding());
request.setCharacterEncoding("UTF-8");
//value = super.getParameter(name);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return super.getParameter(name);
}
}
使用动态代理来实现实现类的增强
public class GenericEncodingFilter implements Filter {
@Override
public void init(FilterConfig filterConfig) throws ServletException {
}
@Override
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
throws IOException, ServletException {
final HttpServletRequest req = (HttpServletRequest) request;
// 增强req:（使用匿名内部类）
HttpServletRequest myReq = (HttpServletRequest) Proxy.newProxyInstance(req.getClass().getClassLoader(),
req.getClass().getInterfaces(), new InvocationHandler() {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
// 判断执行的方法是否是getParameter:
if("getParameter".equals(method.getName())){
// 调用的是getParameter:需要增强这个方法.
// 判断请求方式是GET还是POST:
String type = req.getMethod();
if("get".equalsIgnoreCase(type)){
String value = (String) method.invoke(req, args);
value = new String(value.getBytes("ISO-8859-1"),"UTF-8");
return value;
}else if("post".equalsIgnoreCase(type)){
req.setCharacterEncoding("UTF-8");
}
}
return method.invoke(req, args);
}
});
chain.doFilter(myReq, response);
}
@Override
public void destroy() {
}
}