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Ϊʲôͬһ¸öJAVA±äÁ¿,JSPǰºóÈ¡µÄÖµ²»Ò»ÖÂ?¸ÃÈçºÎ½â¾ö

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Ϊʲôͬһ¸öJAVA±äÁ¿,JSPǰºóÈ¡µÄÖµ²»Ò»ÖÂ?
JSPÒ³ÃæÀïµÄJAVA´úÂëÊÇ:
String   returnPage   =   null;
if   (session.getAttribute( "returnPage ")   !=   null)
{
returnPage   =   String.valueOf(session.getAttribute( "returnPage "));
session.removeAttribute( "returnPage ");
}


ΪʲôÕâÀïreturnPageÊÇnull
function   go_back()
{
window. <%=returnTarget%> .location.href   =   " <%=returnPage%> ";
}

¿ÉÊÇÕâÀïÈ´Ö´ÐÐÁË
function   init()
{
<%   if   (   returnPage   !=   null   )
  {   %>
document.getElementById( 'return ').focus();
<%   }%>
}

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returnPageÊÇÒ»¸ö×Ö·û´®ÁË¡£

ÓÃ.equals( "null ")À´ÅжϰÉ.
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¿ÉÊÇÕâÀïÈ´Ö´ÐÐÁË
function init()
{
<% if ( returnPage != null )
{ %>
document.getElementById( 'return ').focus();
<% }%>
}
==============================================================
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»¹ÓÐÂ¥ÉϵĴó¸ç,¼´±ãÊÇ×Ö·û´®!=nullҲûʲôÎÊÌâ,û±ØÒªÕâÒ²ÓÃ.equals,ͨ³£ÓÚÅжÏÊDz»ÊÇ " "²ÅÓÃ.equals°É,ÄãÕâÑùЩ,Æñ²»³ÉÁ˵¥´¿ºÍ "null "×Ö·û´®±È½ÏÁË?
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