收获着，记录着......

如果用户直接输入了地址，不也可以直接访问吗？理论上是，我们可以加入session进行跟踪，以杜绝此类型事件发生，我们是不是要把每次对session的判断依次拷到每个页里呢，之后下次需要验证的SESSION换了，我们再换？太浪费了，我的做法是做了一个自定义标签，来解决这个问题。

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.tagext.TagSupport;

public class CheckTag extends TagSupport
{
    private static final long serialVersionUID = 879137944441282895L;
    private String check = "";//用来验证的变量
    private String url = "index.jsp";//出现错误要去的页面
    private String msg = "";//错误的提示
    private String scope = "";//要严整变量的范围
    private String to = "go"; //如果验证失败，是将页面后退，还是定位到哪里？

    public String getTo()
    {
        return to;
    }

    public void setTo( String to )
    {
        this.to = to;
    }

    public String getMsg()
    {
        return msg;
    }

    public void setMsg( String msg )
    {
        this.msg = msg;
    }

    public String getScope()
    {
        return scope;
    }

    public void setScope( String scope )
    {
        this.scope = scope;
    }

    public String getCheck()
    {
        return check;
    }

    public void setCheck( String check )
    {
        this.check = check;
    }

    public String getUrl()
    {
        return url;
    }

    public void setUrl( String url )
    {
        this.url = url;
    }

    public int doStsrtTag() throws JspException
    {
        return SKIP_BODY;
    }

    public int doEndTag() throws JspException
    {
        boolean valid = false;//先设为不可用
        if ( scope.equalsIgnoreCase( "request" ) )//如果要检查request范围
        {
            valid = CheckUtil.checkRequestAttribute( pageContext.getRequest(),
                    check );
        }
        else if ( scope.equalsIgnoreCase( "session" ) )
        {
            valid = CheckUtil.checkSession( pageContext.getSession(), check );
        }
        else if ( scope.equalsIgnoreCase( "parameter" ) )
        {
            valid = CheckUtil.checkParameter( pageContext.getRequest(), check );
        }
        else if ( scope.equalsIgnoreCase( "application" ) )
        {
            valid = CheckUtil.checkApp( pageContext.getServletContext(), check );
        }
        if ( valid ) return EVAL_PAGE;//如果可用就继续执行此页的其余部分
        else
        {//否则，哈哈
            try
            {
                if ( to.equalsIgnoreCase( "go" ) ) //现在失败了，就看怎么回到你该到的地方
                    HtmlUtil.callParentGo(
                        pageContext.getOut(), msg, url );//将浏览器定位到URL 
                else
                    HtmlUtil.callBack( pageContext.getOut(), msg );//后退一下页面来阻止
                return SKIP_PAGE;//跳过页面的其余部分，不执行
            }
            catch ( Exception e )
            {
                throw new JspException( e.toString() );
            }
        }
    }

    public void release()
    {
        super.release();
        check = "";
        url = "";
        msg = "";
        scope = "";
    }
}


下面是用到的htmlUtil部分：

public static void callParentGo( Writer out, String msg, String url )
            throws IOException
    {
        out.write( "<script language=\"javascript\">" );
        out.write( "alert(\"" + msg + "\");" );
        out.write( "parent.location.href=\"" + url + "\";" );
        out.write( "</script>" );
    }
public static void callBack( Writer out, String msg ) throws IOException
    {
        out.write( "<script language=\"javascript\">" );
        out.write( "alert(\"" + msg + "\");" );
        out.write( "parent.history.back();" );
        out.write( "</script>" );
    }


写个check.tld部署吧，

<?xml version = "1.0"?>
<taglib>
 <tlibversion>1.0</tlibversion>
 <jspversion>1.1</jspversion>
 <tag>
  <name>check</name>
  <tag-class>com.boya.subject.util.CheckTag</tag-class>
  <attribute>
   <name>check</name>
   <required>true</required>
  </attribute>
  <attribute>
   <name>url</name>
   <required>false</required>
  </attribute>
  <attribute>
   <name>msg</name>
   <required>true</required>
  </attribute>
  <attribute>
   <name>scope</name>
   <required>true</required>
  </attribute>
  <attribute>
   <name>to</name>
   <required>false</required>
  </attribute>
 </tag>
</taglib>


你 只要在每个页面里写下这个就可以判定用户是否登陆了

<%@ taglib prefix="boya" uri="/WEB-INF/check.tld" %>
<boya:check check="admin" msg="管理员尚未登陆，请登陆！" scope ="session"/>

如果没有登陆那么，会自动提示到首页登陆，不错，很完美吧？

当然不是，您可以提出您的见解。。。。