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hello long time not see

sales — Mon, 26 May 2008 10:08:40 +0000

After long time we will start working on this blog again. Be prepared

getServletContext().getAttribute( attribute )); } private String getServerInfoName(String serverInfo) { int

sales — Mon, 05 Feb 2007 02:26:11 +0000

getServletContext().getAttribute( attribute )); } private String getServerInfoName(String serverInfo) { int slash = serverInfo.indexOf( / ); if (slash == -1) return serverInfo; else return serverInfo.substring(0, slash); } private String getServerInfoVersion(String serverInfo) { int slash = serverInfo.indexOf( / ); if (slash == -1) return null; else return serverInfo.substring(slash + 1); } } This servlet also directly subclasses GenericServlet, demonstrating that all the information about a server is available to servlets of any type. The servlet outputs simple raw text. When accessed, this servlet prints something like: req.getServerName(): localhost req.getServerPort(): 8080 getServletContext().getServerInfo(): JavaWebServer/1.1.1 getServerInfo() name: JavaWebServer getServerInfo() version: 1.1.1 getServletContext().getAttribute(”attribute”): null Unfortunately, there is no server-independent way to determine the server’s root directory, referred to in this book as server_root. However, some servers including the Java Web Server save the server’s root directory name in the server.rootsystem property, where it can be retrieved using System.getProperty( server.root ). Locking a Servlet to a Server This server information can be put to more productive uses. Let’s assume you’ve written a servlet and you don’t want it running just anywhere. Perhaps you want to sell it and, to limit the chance of unauthorized copying, you want to lock the servlet to your customer’s machine with a software license. Or, alternatively, you’ve written a license generator as a servlet and want to make sure it works only behind your firewall. This can be done relatively easily because a servlet has instant access to the information about its server. Example 4-4 shows a servlet that locks itself to a particular server IP address and port number. It requires an init parameter key that is appropriate for its server IP address and port before it unlocks itself and handles a request. If it does not receive the appropriate key, it refuses to continue. The algorithm used to map the key to the IP address and port (and vice-versa) must be secure. Example 4-4. A servlet locked to a server import java.io.*; import java.net.*; import java.util.*; import javax.servlet.*; public class KeyedServerLock extends GenericServlet { // This servlet has no class or instance variables // associated with the locking, so as to simplify // synchronization issues.
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There are four methods that a servlet can

sales — Sun, 04 Feb 2007 16:01:50 +0000

There are four methods that a servlet can use to learn about its server: two that are called using the ServletRequestobject passed to the servlet and two that are called from the ServletContextobject in which the servlet is executing. A servlet can get the name of the server and the port number for a particular request with getServerName()and getServerPort(), respectively: public String ServletRequest.getServerName() public int ServletRequest.getServerPort() These methods are attributes of ServletRequestbecause the values can change for different requests if the server has more than one name (a technique called virtual hosting). The returned name might be something like www.servlets.com” while the returned port might be something like 8080 . The getServerInfo()and getAttribute()methods of ServletContextprovide information about the server software and its attributes: public String ServletContext.getServerInfo() public Object ServletContext.getAttribute(String name) getServerInfo()returns the name and version of the server software, separated by a slash. The string returned might be something like JavaWebServer/1.1.1 . getAttribute()returns the value of the named server attribute as an Objector nullif the attribute does not exist. The attributes are server- dependent. You can think of this method as a back door through which a servlet can get extra information about its server. Attribute names should follow the same convention as package names. The package names java.* and javax.*are reserved for use by the Java Software division of Sun Microsystems (formerly known as JavaSoft), and com.sun.*is reserved for use by Sun Microsystems. See your server’s documentation for a list of its attributes. Because these methods are attributes of ServletContextin which the servlet is executing, you have to call them through that object: String serverInfo = getServletContext().getServerInfo(); The most straightforward use of information about the server is an “About This Server” servlet, as shown in Example 4-3. Example 4-3. Snooping the server import java.io.*; import java.util.*; import javax.servlet.*; public class ServerSnoop extends GenericServlet { public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { res.setContentType( text/plain ); PrintWriter out = res.getWriter(); out.println( req.getServerName(): + req.getServerName()); out.println( req.getServerPort(): + req.getServerPort()); out.println( getServletContext().getServerInfo(): + getServletContext().getServerInfo()); out.println( getServerInfo() name: + getServerInfoName(getServletContext().getServerInfo())); out.println( getServerInfo() version: + getServerInfoVersion(getServletContext().getServerInfo())); out.println( getServletContext().getAttribute( attribute ): +
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Example 4-2. Getting init parameter names import java.io.*;

sales — Sun, 04 Feb 2007 03:59:44 +0000

Example 4-2. Getting init parameter names import java.io.*; import java.util.*; import javax.servlet.*; public class InitSnoop extends GenericServlet { // No init() method needed public void service(ServletRequest req, ServletResponse res) throws ServletException, IOException { res.setContentType( text/plain ); PrintWriter out = res.getWriter(); out.println( Init Parameters: ); Enumeration enum = getInitParameterNames(); while (enum.hasMoreElements()) { String name = (String) enum.nextElement(); out.println(name + : + getInitParameter(name)); } } } Notice that this servlet directly subclasses GenericServlet, showing that init parameters are available to servlets that aren’t HTTP servlets. A generic servlet can be used in a web server even though it lacks any support for HTTP-specific functionality. Unfortunately, there’s no server-independent way for a servlet to ask for its registered name or its class file location. This information may be added in a future version of the Servlet API. Until then, although it’s not pretty, this information can be passed using init parameters where necessary. Also, some servers including the Java Web Server provide a back door whereby a servlet can get its registered name. If a servlet defines a method with the following signature, the server calls it and passes it the servlet’s registered name at initialization: public void setServletName(String name); The servlet can save the passed-in name and use it later. You’ll notice this back door was built without changing the Servlet API, a necessary requirement because, by the time it was added, the Servlet API 2.0 had already been frozen. The Server A servlet can find out much about the server in which it is executing. It can learn the hostname, listening port, and server software, among other things. A servlet can display this information to a client, use it to customize its behavior based on a particular server package, or even use it to explicitly restrict the machines on which the servlet will run. Getting Information about the Server
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Each registered servlet name can have specific initialization

sales — Sat, 03 Feb 2007 17:26:58 +0000

Each registered servlet name can have specific initialization (init) parameters associated with it. Init parameters are available to the servlet at any time; they are often used in init ()to set initial or default values for a servlet or to customize the servlet’s behavior in some way. Init parameters are more fully explained in Chapter 3, The Servlet Life Cycle. Getting an Init Parameter A servlet uses the getInitParameter()method to get access to its init parameters: public String ServletConfig.getInitParameter(String name) This method returns the value of the named init parameter or nullif it does not exist. The return value is always a single String. It is up to the servlet to interpret the value. The GenericServletclass implements the ServletConfiginterface and thus provides direct access to the getInitParameter()method.* The method is usually called like this: public void init(ServletConfig config) throws ServletException { super.init(config); String greeting = getInitParameter(”greeting”); } A servlet that needs to establish a connection to a database can use its init parameters to define the details of the connection. We can assume a custom establishConnection()method to abstract away the details of JDBC, as shown in Example 4-1. * The servlet must call super.init(config)in its init()method to get this functionality. Example 4-1. Using init parameters to establish a database connection java.sql.Connection con = null; public void init(ServletConfig config) throws ServletException { super.init(config); String host = getInitParameter( host ); int port = Integer.parseInt(getInitparameter( port )); String db = getInitParameter( db ); String user = getInitParameter( user ); String password = getInitParameter( password ); String proxy = getInitParameter( proxy ); con = establishConnection(host, port, db, user, password, proxy); } Getting Init Parameter Names A servlet can examine all its init parameters using getInitParameterNames(): public Enumeration ServletConfig.getInitParameterNames() This method returns the names of all the servlet’s init parameters as an Enumerationof Stringobjects or an empty Enumerationif no parameters exist. It’s most often used for debugging. The GenericServletclass also makes this method directly available to servlets. Example 4-2 shows a servlet that prints the name and value for all of its init parameters.

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