Static fields in JSP declaration
<%!
class father {
static int s = 0;
}
%>
<%
father f1 = new father();
father f2 = new father();
f1.s++;
out.println(f2.s); // It must print "1"
%>
When I r开发者_运维百科un the file, I got this error. Can anybody explain?
The field s cannot be declared static; static fields can only be declared in static or top level types.
Using <%! ... %> syntax you decalre an inner class, which is non-static by default, so it can't contain static fields. To use static fields, you should declare the class as static:
<%!
static class father {
static int s = 0;
}
%>
However, BalusC's advice is right.
Don't do this in a JSP. Create a real Java class, if need be in flavor of a Javabean.
public class Father {
private static int count = 0;
public void incrementCount() {
count++;
}
public int getCount() {
return count;
}
}
and use a Servlet class to do the business task:
public class FatherServlet extends HttpServlet {
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Father father1 = new Father();
Father father2 = new Father();
father1.incrementCount();
request.setAttribute("father2", father2); // Will be available in JSP as ${father2}
request.getRequestDispatcher("/WEB-INF/father.jsp").forward(request, response);
}
}
which you map in web.xml as follows:
<servlet>
<servlet-name>fatherServlet</servlet-name>
<servlet-class>com.example.FatherServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>fatherServlet</servlet-name>
<url-pattern>/father</url-pattern>
</servlet-mapping>
and create /WEB-INF/father.jsp as follows:
<!doctype html>
<html lang="en">
<head>
<title>SO question 2595687</title>
</head>
<body>
<p>${father2.count}
</body>
</html>
and invoke the FatherServlet by http://localhost:8080/contextname/father. The ${father2.count} will display the return value of father2.getCount().
To learn more about programming JSP/Servlets the right way, I recommend you to get yourself through those tutorials or this book. Good luck.
加载中,请稍侯......
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