通过Java Web Filter实现一个最简单的UrlRewrite过滤器

工具：支持JavaEE的Eclipse IDE

Web 过滤器可以通过动态Web项目来直接添加；或者直接创建Java项目通过添加类来完成，参看如下过滤器代码：

package me.ereach.urlfilter;

import java.io.IOException;
import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.annotation.WebFilter;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

@WebFilter(
	filterName = "Filter01",
	urlPatterns = {"/*"}
)
public class Filter01 implements Filter {
	private FilterConfig fc;

	public void init(FilterConfig fConfig) throws ServletException {
		this.fc = fConfig;
	}

	public void doFilter(ServletRequest request,
			ServletResponse response, FilterChain chain)
			throws IOException, ServletException {
		HttpServletRequest httprequest = (HttpServletRequest)request;
		HttpServletResponse httpresponse = (HttpServletResponse)response;

		String contextPath = httprequest.getContextPath();
		String servletPath = httprequest.getServletPath();

		if (servletPath.startsWith("/hallo/")) {
			int l = servletPath.length();
			String next = contextPath + servletPath.substring(4);

			RequestDispatcher dispatcher = fc.getServletContext().getRequestDispatcher(next);
			dispatcher.forward(request,response);

			return;
		}
		else if (servletPath.startsWith("/welcom/hi/")) {
			int l = servletPath.length();
			String next = contextPath + servletPath.substring(9);

			RequestDispatcher dispatcher = fc.getServletContext().getRequestDispatcher(next);
			dispatcher.forward(request,response);

			return;
		}

		chain.doFilter(request, response);
	}

	@Override
	public void destroy() {
		// TODO Auto-generated method stub

	}
}

该过滤器非常简单，所有转发的Url都写在代码里，因此，只要注册了这个过滤器就可以直接使用了。使用这个过滤器还需以下几个步骤：

1. 导出这个过滤器为一个jar文件。
2. 把这个jar拷贝到Web App的WEB-INF/lib
3. 在WEB-INF/web-xml中注册这个jar
4. 设置context-root为"/"
5. 重启Web App以使设置生效