java 过滤器(Filter)

java过滤器有很多用处比如:一些需要过滤器的情况: 
    (1)认证Filter
    (2)日志和审核Filter
    (3)图片转换Filter
    (4)数据压缩Filter
    (5)密码Filter
    (6)令牌Filter
    (7)触发资源访问事件的Filter
    (8)XSLT Filter
    (9)媒体类型链Filter

此篇文章用Filter来处理乱码问题

使用Filter步骤处理乱码步骤

1.创建实现Filter接口

2.先在web.xml中做好配置,filter 配置路径/* (放在过滤器的第一个位置) 
3.在filter中重写getParameter(使用装饰着设计模式) 
4.在filter中, 对request进行加强.

实现Filter接口的EncodeFilter类

package 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;
import javax.servlet.http.HttpServletResponse;

public class EncodeFilter implements Filter{

	@Override
	public void destroy() {
		// TODO Auto-generated method stub
		System.out.println("Filter销毁>>>>>>");
	}

	//处理post提交乱码
	@Override
	public void doFilter(ServletRequest request, ServletResponse response,
			FilterChain chain) throws IOException, ServletException {
		// TODO Auto-generated method stub
		//强转
		System.out.println("对servlet进行拦截>>>>>>");

		HttpServletRequest  req=(HttpServletRequest)request;
		HttpServletResponse res=(HttpServletResponse)response;
		String method=req.getMethod();
		
		
		res.setContentType("text/html;charset=utf-8");
        System.out.println("这里是filter>>>>>>>>>>>>>>>>>");
		System.out.println("对servlet进行释放>>>>>>");
		chain.doFilter(req,res);

		
	}

	@Override
	public void init(FilterConfig arg0) throws ServletException {
		// TODO Auto-generated method stub
		System.out.println("Filter初始化工作>>>>>");
		
	}

	
}

装饰者MyFilter.java强化了Parameter()和getParameterValues()方法

package Filter;

import java.io.UnsupportedEncodingException;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletRequestWrapper;

public class MyFilter extends HttpServletRequestWrapper {

	private HttpServletRequest request;

	public MyFilter(HttpServletRequest request) {
		super(request);
		this.request = request;
	}

	// 重写getParamter方法,处理实现get方式提交时的乱码
	@Override
	public String getParameter(String name) {
		// 如果为请求为Post提交
		if (this.request.getMethod().equalsIgnoreCase("post")) {
			try {
				this.request.setCharacterEncoding("utf-8");
				return this.request.getParameter(name);
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}

		String value = this.request.getParameter(name);
		if (value == null) {
			return null;
		}
			
		if(this.request.getMethod().equalsIgnoreCase("get")){
			try {
				value = new String(value.getBytes("ISO-8859-1"), "utf-8");
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}


		return value;
	}

	@Override
	public String[] getParameterValues(String name) {
		// 如果为请求为Post提交
		if (this.request.getMethod().equalsIgnoreCase("post")) {
			try {
				this.request.setCharacterEncoding("utf-8");
				System.out.println("编码设置成功!>>>>>>>>>>>>>>>");
			
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		
		String[] value =this.request.getParameterValues(name);
		if (value == null) {
			return null;
		}
		
		if(this.request.getMethod().equalsIgnoreCase("get")){
			
			try {
				for(int i=0;i<value.length;i++){
					value[i]= new String(value[i].getBytes("ISO-8859-1"), "utf-8");					
				}
			} catch (UnsupportedEncodingException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		
		}
		
		return value;
	}

}