Servlet过滤器、包装器

使用Filter进行转码，首先在web.xml中对Filter进行部署

    deCode
    cn.com.Demo.Filter.DeCode
    
        code
        UTF-8
    



    deCode
    /*

然后新建一个Class实现Filter接口，其中需要注意的是，req.setCharacterEncoding()只支持post方法，如要get和post都支持可以采用第一种方法是从requset中将参数获取出来，然后手动转码（从iso-8859-1转为utf-8），因为request也是一个作用域对象，所以可以用来传递已经转码后的参数，使用setAttribute，有一点需要注意的是在获取参数时，原本的request.getParameter()就应该对应更改为request.getAttribute()。

public class DeCode implements Filter{
    
    private String code = "UTF-8";
    
    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        System.out.println("进入过滤器");
        //req.setCharacterEncoding(code); 只支持post方法
        
        Enumeration paraNames = req.getParameterNames();
        while(paraNames.hasMoreElements())
        {
            String paraName = paraNames.nextElement();
            String value = req.getParameter(paraName);
            byte[] bytes = value.getBytes("iso-8859-1");
            value = new String(bytes,"utf-8");
            req.setAttribute(paraName,value);
        }
        
        res.setContentType("text/html;charset="+code);
        chain.doFilter(req, res);
        
    }

    @Override
    public void init(FilterConfig cfg) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("初始化过滤器");
        String encode = cfg.getInitParameter("code");
        if(encode!=null)
        {
            System.out.println("当前编码为"+encode);
            this.code = encode;
        }
    }

由于第一种方法需要将每个servlet中的getParameter改为getAttribute，所以推荐使用第二种方法Wrapper（包装器）。
代码如下：

public class DeCode implements Filter{
    
    private String code = "UTF-8";
    
    @Override
    public void destroy() {
        // TODO Auto-generated method stub
        
    }

    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain chain) throws IOException, ServletException {
        // TODO Auto-generated method stub
        System.out.println("进入过滤器");    
        
    /*  new包装器,此处需要注意，因为doFilter中是ServletRequest，
     * 所以要将其转换为HttpServletRequest*/
        MyRequestWrapper reqWrapper = new MyRequestWrapper((HttpServletRequest)req);
        res.setContentType("text/html;charset="+code);
        chain.doFilter(reqWrapper, res);//将request替换成包装器的reqWrapper
        
    }

    @Override
    public void init(FilterConfig cfg) throws ServletException {
        // TODO Auto-generated method stub
        System.out.println("初始化过滤器");
        String encode = cfg.getInitParameter("code");
        if(encode!=null)
        {
            System.out.println("当前编码为"+encode);
            this.code = encode;
        }
    }
    
    
    /*包装器内置类*/
    private class MyRequestWrapper extends HttpServletRequestWrapper
    {

    

        public MyRequestWrapper(HttpServletRequest request) {
            super(request);
            // TODO Auto-generated constructor stub
        }

        @Override
        public String getParameter(String name) {
            String value = super.getParameter(name);
            value = this.myEnCoding(value);
            return value;
        }
        
        @Override
        public String[] getParameterValues(String name) {
            String[] values = super.getParameterValues(name);
            if(values != null)
            {
                for(String value:values)
                {
                    value=this.myEnCoding(value);
                }
            }
            return values;
        }

        private String myEnCoding(String value)
        {
            if(value != null)
            {   
                try{
                byte[] bytes = value.getBytes("iso-8859-1");
                value = new String(bytes,code);
                }catch (Exception e) {
                    // TODO: handle exception
                }
            }
            return value;   
        }
    }

}

通过过滤器对登陆权限进行控制

通过设置一个过滤器，请求中没有登陆信息时则返回到登陆界面。
代码如下：

public class LoginControlFilter implements Filter{

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

    @Override
    public void doFilter(ServletRequest req, ServletResponse res,
            FilterChain arg2) throws IOException, ServletException {
        // TODO Auto-generated method stub
        //判断是否有登陆
        HttpServletRequest request = (HttpServletRequest)req;
        HttpSession session = request.getSession();
        String userName = (String)session.getAttribute("LOGIN_USER");
        if(userName != null&&!"".equals(userName))
        {
            //如有登陆则继续调用后续
            arg2.doFilter(req, res);
        }else
        {
            //如没登陆则跳转到LoginServlet
            req.getRequestDispatcher("/loginServlet").forward(req, res);
        }
    }

    @Override
    public void init(FilterConfig arg0) throws ServletException {
        // TODO Auto-generated method stub
        
    }

}

在Web.xml中进行如下配置

    LoginControlFilter
    cn.com.Demo.Filter.LoginControlFilter


    LoginControlFilter
    /*