A servlet is a normal Java class, so when there are no custom constructors, there is an implicit default constructor with no arguments. Servlet containers typically use the Class.newInstance() method to load servlets, so you must be careful to add an explicit default constructor if you add non-default constructors.

All those "cannot find symbol" error messages mean that you do not have the Java servlet JAR file on your compiler's classpath, so it cannot find the servlet class files. The servlet JAR file is normally distributed with your servlet container. For Apache Tomcat it is a file named {CATALINA_HOME}/common/lib/servlet-api.jar. Add this to your compiler classpath as follows.

Servlets are normal Java classes, they compile and run just like any other class. All that is required is that servlets implement the javax.servlet.Servlet interface. Usually, they extend a protocol-specific class such as javax.servlet.http.HttpServlet.

To compile a servlet, you will need to have the Java Servlet API classes in your classpath. Most Java servlet containers come with a copy, it may be called servlet.jar or something similar. The basic classes are in the packages javax.servlet and javax.servlet.http.

Even though there is an init method in a servlet which gets called to initialise it, a constructor is still required to instantiate the servlet. Even...

Yes , of course you can use the constructor instead of init(). There’s nothing to stop you. But you shouldn’t. The original reason for init() was that ancient versions of Java couldn’t dynamically invoke constructors with arguments, so there was no way to give the constructur a ServletConfig. That no longer applies, but servlet containers still will only call your no-arg constructor. So you won’t have access to a ServletConfig or ServletContext.

This might be either because it's completely unknown or because the specific environment (include files, OS version, et cetera) isn't explicitly handled. If this happens, you may need to port the server to your OS yourself. Some operating systems include a default C compiler that is either not ANSI C-compliant or suffers from other deficiencies. The usual recommendation in cases like this is to acquire, install, and use gcc.

In the Java servlet API there are several sub-interfaces and implementations of the Servlet interface. The GenericServlet class has general purpose implementations of servlet methods that are common to all, including getInitParameter(String), init(ServletConfig) and log(String). GenericServlet is abstract and leaves the key method service(ServletRequest, ServletResponse) abstract for sub-class implementation.

You can configure custom error pages in Tomcat using the error-page element in the application's web.xml file, as below. The error-code element contains the HTTP status code number, the location element contains the path to the error document relative to the Web application root. The error document may be a static HTML document or a JSP. The error-page element may be repeated to specify custom pages for any number of error codes.

The key steps in creating and running a servlet are outlined below in the simplest form. There are different techniques that can be used to complete these stages, described in other FAQ answers. Create a Web application directory structure under the webapp directory of your servlet container (or use an existing one), e.g.

URL-rewriting is a way of maintaining a session between an HTTP client and a servlet container which does not use cookies. Rather than exchange a session ID in a cookie, the servlet container includes it in the hyperlink URLs it generates for servlets and JSP.

There are many fundamental differences between Applet and Servlet classes, the Java API documentation for the two types will show you they have little in common. Applets are essentially graphical user interface (GUI) applications that run on the client side in a network environment, typically embedded in an HTML page. Applets are normally based on Abstract Windowing Toolkit components to maintain backward-compatibility with the widest range of browsers' Java implementations.

The class structure of servlets is fundamentally the same as any other Java class, however they must fulfil the Servlet and GenericServlet interface. These interfaces define a set of so-called lifecycle methods, a service method and various supporting methods for getting servlet configuration parameters and for logging. The lifecycle methods init(ServletConfig) and destroy() are called when the servlet container first puts the servlet into service and ultimately removes it.

You are probably missing popt.h, which newt needs to compile, it can be found in the 'popt' package. Check your distribution and see if they have popt, if not check Related Linux Packages to see where you can get it. You should have used CD-RW. ;) In the HOWTO, it gives instructions on how to create a test CD (one, not six).

When you have a number of constructors in a class you can call them using this() in a similar way to the superclass constructor super(). For instance, if you have a "good citizen" constructor that takes a String and a boolean, and a shorthand version that only takes a String, you may pass a default value to the two argument constructor, like so:

If you are using a 64-bit OS, you need to add the -o32' option for the compiler, or use gcc. With the SGI compiler, you may also need to play with optimization. Some modules may have exhibit problems unless compiled with -O1' or even '-O0'. Script-Fu requires the POSIX-compliant regex functions, which SGI only supports with IRIX 6.2 and later versions. The GNU version of regex should work just fine, though, and is available at:

One way to accomplish this is to have the applets communicate via TCP/IP sockets to the servlet. The servlet would then use a custom protocol to receive and push information between applets. However, this solution does have firewall problems if the system is to be used over and Internet verses an Intranet.

In general, look at each frame as a unique document capable of sending its own requests and receiving its own responses. You can create a top servlet (say, FrameServlet) that upon invocation creates the frame layout you desire and sets the SRC parameters for the frame tags to be another servlet, a static page or any other legal value for SRC.

Your compilation classpath only needs to include the classes and libraries necessary for your servlet. It's unlikely you are using Tomcat bootstrap classes in your servlet but, if so, make sure this package is on your classpath. The URL you use partly depends on the port you have configured Tomcat to operate on. This is configured in the HTTP Connector element in server.xml.

A1: No. In Holland where both Marijuana and Heroin are legally available, they have HALF the percentage of Marijuana users as in the US, and a THIRD the percentage of heroin users. A2: If heroin were legal tomorrow would you shoot up? No, neither would I. The people that would use heroin already use it, and obtain it through the black market.

Some people feel you should not use the this pointer in a constructor because the object is not fully formed yet. However you can use this in the constructor (in the {body} and even in the initialization list) if you are careful. Here is something that always works: the {body} of a constructor (or a function called from the constructor) can reliably access the data members declared in a base class and/or the data members declared in the constructor's own class.

The security in a browser is designed to restrict you from automating things like this. However, you can use JavaScript in the HTML your servlet returns to print a frame. The browser will still confirm the print job with the user, so you can't completely automate this. Also, you'll be printing whatever the browser is displaying (it will not reliably print plug-ins or applets), so normally you are restricted to HTML and images.

Another common failure, for some WML pages, is seen when the wapbox log-file read something like "WML compiler: Parsing failed, no parsed document." Here, the libxml parser failed to understand the WML page, for some reason. Either the page is really malformed, or libxml has a problem. use 'xml-config --version' or 'rpm -q libxml', 'rpm -q libxml2', 'rpm -q libxml-devel' or 'rpm -q libxml2-devel' to find out whether libxml is installed on your system at all, and to see which version it is at.

Make sure that if you don't already have Kogut installed that you're using the bootstrapped version of Kogut. Also make sure that you have a few basic Unix utilities: a C compiler, make, and a Bourne or Bash-style shell. If you're on Windows or Mac OS X, this probably means downloading Cygwin or Fink to get these tools. If all else fails, post your error to the Kogut mailing list.

The compiler found a symbol that it wasn't expecting.. for example, an extra paren on a complex if check, a semicolon placed after a function body header, a semicolon omitted from the previous line amongst others. The error is not always on the line mentioned by gcc, but may be the previous line. This error arises when you assign a pointer to a non-pointer variable.

First, download the sources. Then type make. It should produce nw802.o and usbvideo.o . Then modprobe videodev, insmod usbvideo.o & insmod nw802.o . Now the module is loaded. usbvideo.c & usbvideo.h are included in the CVS tree & in the packages but these files are actually part of the kernel tree. I included them because they may have not been built with your kernel. If you wish, you can copy these from /usr/src/linux/drivers/usb/ (eg. to get newer versions.

In object-oriented programming, an object's constructor is responsible for initializing the object completely at creation time. The constructor receives the list of options passed to the snit::type command's create method and can then do whatever it likes. That might include computing instance variable values, reading data from files, creating other objects, updating type and instance variables, and so forth.

The Polynomial(int d, double *coefs) constructor is invoked when an object of type Polynomial is defined using the appropriate arguments. For example, double co[] = { 1.2, 3.4, 5.6 }; Polynomial p(2, co); constructs p to represent 5.6x2 + 3.4 x + 1.2.

If the end result needed is to invoke the methods then the simplest mechanism would be to treat the servlet like any java object , create an instance and call the mehods. If the idea is to call the service method from the service method of another servlet, AKA forwarding the request, you could use the RequestDispatcher object. If, however, you want to gain access to the instance of the servlet that has been loaded into memory by the servlet engine, you have to know the alias of the servlet.

The driver works perfectly in servlets just as in an ordinary application, provided the classpath is set properly and the server component running.