通过filter修改提交过来的数据

request.getParameter可以获取到前台提交到的数据。
如果想对数据处理，进行一些安全方面的转义，这样可以通过较少的代码修改来实现。
在实现的时候，发现request对象并没有提供setParameter方法让我们来修改参数内容。
我们可以通过以下方式来实现。
1.新建立一个项目，项目名称webProject
2.index.jsp里代码如下，打印接收到的参数内容

<%
String name=request.getParameter("username");
System.out.println("name:"+name);
%>

3.访问http://localhost:8080/webProject/index.jsp?username=123<a><input>，结果为

name:123<a><input>

4.在web.xml里添加一个filter

   <filter>
   <filter-name>securityFilter</filter-name>
   <filter-class>info.frady.SecurityFilter</filter-class>

  </filter>
  <filter-mapping>
    <filter-name>securityFilter</filter-name>
    <url-pattern>/*</url-pattern>
</filter-mapping>

5.SecurityFilter的代码如下

package info.frady;


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 SecurityFilter implements Filter {
    private FilterConfig filterConfig;
    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // TODO Auto-generated method stub
        this.filterConfig = filterConfig;

    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
    	SecirityHttpServletRequestWrapper requestwrapper = new SecirityHttpServletRequestWrapper((HttpServletRequest)request);

    //对自定义装饰器初始化后，继续发关原先的请求，不过将ServletRequest request  改为自定义装饰器的对像requestwrapper
    chain.doFilter(requestwrapper, response);
    }

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

    }

}

6.SecirityHttpServletRequestWrapper为自定义的类，继承自HttpServletRequestWrapper
代码如下：

package info.frady;

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

public class SecirityHttpServletRequestWrapper extends HttpServletRequestWrapper {

	public SecirityHttpServletRequestWrapper(HttpServletRequest request) {
		super(request);
	}
	//覆写getParameter方法
    @Override
    public String getParameter(String name) {
    	String postValue=super.getParameter(name);
    	postValue=postValue.replace("<", "&lt;").replace(">", "&gt;");
        return postValue;
    }

}

7.访问http://localhost:8080/webProject/index.jsp?username=123<a><input>，结果为

name:123<a><input>