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How are path related values of the request object changed after a forward or include?
The values of getRequestURI() and other path related method's change for a forward(), but remain the same for an include().
| include |
When a servlet (or jsp) has been invoked by an include, the path related methods of the request object correspond to the invoking servlet. Request attributes javax.servlet.include.* contain values corresponding to the target.
| getXXXX() methods | invoking servlet |
| javax.servlet.include. | target |
<jsp:include page="target.jsp"/> |
| request.getRequestURI() | /testapp/index.jsp |
| request.getContextPath() | /testapp |
| request.getServletPath() | /index.jsp |
| request.getPathInfo() | null |
| request.getQueryString() | null |
| request.getAttribute("javax.servlet.include.request_uri") | /testapp/target.jsp |
| request.getAttribute("javax.servlet.include.context_path") | /testapp |
| request.getAttribute("javax.servlet.include.servlet_path") | /target.jsp |
| request.getAttribute("javax.servlet.include.path_info") | null |
| request.getAttribute("javax.servlet.include.query_string") | null |
| forward |
When a servlet (or jsp) has been invoked by a forward, the path related methods of the request object return the path of the target servlet. Request attributes javax.servlet.forward.* contain values corresponding to the invoking servlet.
| getXXXX() methods | target |
| javax.servlet.forward. | invoking servlet |
From the discussion of forward() in the Servlet specification:
The path elements of the request object exposed to the target servlet must reflect the path used to obtain the RequestDispatcher.
<jsp:forward page="target.jsp"/> |
| request.getRequestURI() | /testapp/target.jsp |
| request.getContextPath() | /testapp |
| request.getServletPath() | /target.jsp |
| request.getPathInfo() | null |
| request.getQueryString() | null |
| request.getAttribute("javax.servlet.forward.request_uri") | /testapp/index.jsp |
| request.getAttribute("javax.servlet.forward.context_path") | /testapp |
| request.getAttribute("javax.servlet.forward.servlet_path") | /index.jsp |
| request.getAttribute("javax.servlet.forward.path_info") | null |
| request.getAttribute("javax.servlet.forward.query_string") | null |
| caucho.forward | true |
| Exception: getNamedDispatcher() |
If getNamedDispatcher() is used to obtain a dispatcher to do the include() or forward(), no attributes are set.
| Request parameters |
A call to forward() or include() can contain parameters in the url. These parameters are returned with a subsequent call to request.getParameter().
The value of request.getQueryString(), however, depends on whether an include() or a forward() was done, and you may end up with the bizarre situation where the value of request.getParameter() does not match the value in the query string.
| called with url | /testapp/index.jsp?foo=original |
| index.jsp contains | <jsp:include page="target.jsp"/> |
| request.getQueryString() in target.jsp returns | foo=original |
| request.getParameter("foo") in target.jsp returns | original |
| request.getAttribute("javax.servlet.include.query_string") in target.jsp returns | null |
| called with url | /testapp/index.jsp?foo=original |
| index.jsp contains | <jsp:include page="target.jsp?foo=override"/> |
| request.getQueryString() in target.jsp returns | foo=original |
| request.getParameter("foo") in target.jsp returns | override |
| request.getAttribute("javax.servlet.include.query_string") in target.jsp returns | foo=override |
| called with url | /testapp/index.jsp?foo=original |
| index.jsp contains | <jsp:foward page="target.jsp"/> |
| request.getQueryString() in target.jsp returns | null |
| request.getParameter("foo") in target.jsp returns | original |
| request.getAttribute("javax.servlet.forward.query_string") in target.jsp returns | foo=original |
| called with url | /testapp/index.jsp?foo=original |
| index.jsp contains | <jsp:foward page="target.jsp?foo=override"/> |
| request.getQueryString() in target.jsp returns | foo=override |
| request.getParameter("foo") in target.jsp returns | override |
| request.getAttribute("javax.servlet.forward.query_string") in target.jsp returns | foo=original |
Class.forName() doesn't seem to work right
Class.forName(String) has a bit of an obscure feature, it uses the "defining classloader of the current class" when it searches for the class.
To successfully accomplish the functionality of Class.forName() in all circumstances, you can use:
private Class classForName(String classname)
{
ClassLoader loader = Thread.currentThread().getContextClassLoader();
if (loader != null)
_theClass = Class.forName(classname, false, loader);
else
theClass = Class.forName(classname);
}
|
Why do I have to put my classes in a package?
Starting with Java 1.4 the use of classes that are not in a package (sometimes called the "default" package") is deprecated. Java classes should always be in a package. In some version of Java, packageless classes are not going to be supported at all.
The solution is to put all of your classes in a package.
See http://java.sun.com/j2se/1.4/compatibility.html, point #8, second bullet point.
How do I specify the default file encoding?
The default file encoding for the JVM is set with the system property file.encoding. The JDK will only pick up that system property if it is specified at startup:
$ bin/httpd -Dfile.encoding=ISO-8859-1 |
A simple JSP can be used to determine the default encoding that is being used:
<%@ page session="false" import="java.io.*" %>
System.getProperty("file.encoding"):
<%= System.getProperty("file.encoding") %>
<p>
OutputStreamWriter encoding is:
<%= (new OutputStreamWriter(new ByteArrayOutputStream())).getEncoding() %>
|
System.getProperty("file.encoding"): ISO-8859-1
OutputStreamWriter encoding is: ISO8859_1
|
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