过滤器Filter也具有生命周期：init()->doFilter()->destroy()，由部署文件中的filter元素驱动。在servlet2.4中，过滤器同样可以用于请求分派器，但须在web.xml中声明，INCLUDE或FORWARD或REQUEST或ERROR该元素位于filter-mapping中。

一、批量设置请求编码

Java代码
public class EncodingFilter implements Filter {

private String encoding = null;

public void destroy() {
encoding = null;
}

public void doFilter(ServletRequest request, ServletResponse
response,
FilterChain chain) throws IOException, ServletException {

String encoding = getEncoding();
if (encoding == null){
encoding = "gb2312";
}
request.setCharacterEncoding(encoding);// 在请求里设置上指定的编码
chain.doFilter(request, response);
}

public void init(FilterConfig filterConfig) throws ServletException
{
this.encoding = filterConfig.getInitParameter("encoding");
}

private String getEncoding() {
return this.encoding;
}

}
public class EncodingFilter implements Filter {
private String encoding = null;
public void destroy() {
encoding = null;
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
String encoding = getEncoding();
if (encoding == null){
encoding = "gb2312";
}
request.setCharacterEncoding(encoding);// 在请求里设置上指定的编码
chain.doFilter(request, response);
}
public void init(FilterConfig filterConfig) throws ServletException {
this.encoding = filterConfig.getInitParameter("encoding");
}
private String getEncoding() {
return this.encoding;
}
}

Xml代码

EncodingFilter
com.logcd.filter.EncodingFilter

encoding
gb2312




EncodingFilter
/*


EncodingFilter
com.logcd.filter.EncodingFilter

encoding
gb2312



EncodingFilter
/*

二、用filter控制用户访问权限