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It is your browser that converts a URL such as =dark&taste=malty into the GET request that you see here, with the HTTP method on the first line followed by the path, parameters, and protocol version, and a sequence of request headers. Not shown is the fact that following the request headers there needs to be one extra "blank line" (i.e. a carriage return/line feed combination) to mark the end of the HTTP request in the TCP data stream.

web.xml file is the deployment descriptor of the web application and contains a mapping for servlets (prior to 3.0), welcome pages, security configurations, session timeout settings, etc. Thats all for the java web application startup tutorial, we will explore Servlets and JSPs more in future posts. Update: Next tutorial in this series is Java Servlets Tutorial

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What is CGI? A webserver feature that allows programs to run alongside/inside the webserver. The programs can be written in any language. Sometimes the languages are interpreted (Perl, Java, Tcl, VB); sometimes compiled (C, C++). The webserver passes Form data to these programs, and the programs write output directly to the invoking Browser. Exercise 5:(Solution): Examine the search query at www.yahoo.com Which of GET or POST is being used? How does a webserver call a CGI program? Three possible ways: By forking a new process: Usually for C/C++ CGI programs. The webserver forks off a new (shell) process which starts execution of the C program. The forking is performed for each HTTP request. Forking is expensive. Wasteful for CGI programs that run repeatedly. By pre-loading the program when the webserver is started: For commonly-used programs, the code can be rolled into the webserver. Then, the CGI program is really part of the webserver. Extremely efficient since it is already loaded. Can crash the webserver if badly written. Changing the program requires re-starting the webserver. Dynamic one-time loading: The CGI program is loaded when first called. Subsequent requests simply multi-thread the already-loaded program. If the program is changed, it is re-loaded without bringing the webserver down. Interpreted languages make this option very safe. This is the approach used by Java servlets.

What are Java servlets? Java's solution to CGI programs. Wrong way to use Java as CGI: Write stand-alone Java program. Invoke it via new CGI shell process. The right way:

Use servlets and a servlet-compatible server. How it works: Browser makes a servlet request to webserver. Webserver recognizes the URL as a servlet URL.

(e.g., ) Webserver loads servlet if not already loaded. Servlet executes and delivers output to webserver (HTML output). Webserver delivers output to Browser. What you need to write servlets: Either JDK 1.1 and JSDK (Java Servlet Development Kit). JDK 1.2 A servlet-compatible webserver. Example: HelloWorld servlet import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class helloworld extends HttpServlet { public void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // Set the content type of the response. resp.setContentType ("text/html"); // Create a PrintWriter to write the response. java.io.PrintWriter out = new PrintWriter (resp.getOutputStream()); // The first part of the response. out.println (""); out.println (" Test "); out.println (""); // The greeting. out.println ("Yo, Hello World!"); // Last part. out.println (""); out.println (""); out.close(); // Screen I/O System.out.println ("Inside servlet ... servlet complete"); } public void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet (req, resp); } } So, what are GET and POST? When Form data is sent by the browser, it can be sent in one of two ways: (1) using the GET method and (2) using the POST method. In the GET method, the form data (parameters) is appended to the URL, as in: Here, the text field contains music. In the POST method, the browser simply sends the form data directly. When you create an HTML form, you decide whether you want to use GET or POST. When you use GET, the doGet() method of your servlet is called, otherwise the doPost() method is called. The standard practice is to use POST, unless you need to use GET. You need to use GET when you want a link to invoke a CGI program (servlet).

Now let's write Java - a simple servlet that writes "Hello World!" tothe browser: (source) import javax.servlet.*; import javax.servlet.http.*; import java.io.*; public class HelloWorld extends HttpServlet { public void doGet (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // Set the content type of the response. resp.setContentType ("text/html"); // Create a PrintWriter to write the response. java.io.PrintWriter out = new PrintWriter (resp.getOutputStream()); // The first part of the response. out.println (""); out.println (" Test "); out.println (""); // The greeting. out.println ("Yo, Hello World!"); // Last part. out.println (""); out.println (""); out.close(); // Screen I/O System.out.println ("Inside servlet ... servlet complete"); } public void doPost (HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet (req, resp); } } Note: The servlet class libraries need to be imported, along with java.io.PrintWriter. There are two methods, one for each type of request: GET or POST. You can decide not to "really" implement one method and instead have it call the other. There are two object parameters to each method, the "request" and the "respponse". The HttpServletResponse instance has an OutputStream that is used to write directly to the requesting browser. To make writing easier, we wrap a PrintWriter around the OutputStream instance: // Create a PrintWriter to write the response. java.io.PrintWriter out = new PrintWriter (resp.getOutputStream()); We set the content-type (as required by the HTTP protocol): // Set the content type of the response. resp.setContentType ("text/html"); We write HTML to the output, e.g., out.println (""); out.println (" Test "); Don't forget to close the output stream: out.close(); Optionally, for debugging, we can also write to the local screen where the webserver is running: System.out.println ("Inside servlet ... servlet complete"); Exercise 8: Compile your servlet. Test your servlet.with your assigned port number.

The name of a WebResourcePermission (also referred to as the target name) identifies the Web resources to which the permission pertains. Implementations of this class MAY implement newPermissionCollection or inherit its implementation from the super class.Author:Ron Monzillo, Gary EllisonSee Also:Permission, Serialized FormConstructor SummaryConstructors Constructor and DescriptionWebResourcePermission(HttpServletRequest request)Creates a new WebResourcePermission from the HttpServletRequest object.WebResourcePermission(String name, String actions)Creates a new WebResourcePermission with the specified name and actions.WebResourcePermission(String urlPatternSpec, String[] HTTPMethods)Creates a new WebResourcePermission with name corresponding to the URLPatternSpec, and actions composed from the array of HTTP methods.Method SummaryAll Methods Instance Methods Concrete Methods Modifier and TypeMethod and Descriptionbooleanequals(Object o)Checks two WebResourcePermission objects for equality.StringgetActions()Returns a canonical String representation of the actions of this WebResourcePermission.inthashCode()Returns the hash code value for this WebResourcePermission.booleanimplies(Permission permission)Determines if the argument Permission is "implied by" this WebResourcePermission.Methods inherited from class java.security.PermissioncheckGuard, getName, newPermissionCollection, toStringMethods inherited from class java.lang.Objectclone, finalize, getClass, notify, notifyAll, wait, wait, waitConstructor DetailWebResourcePermissionpublic WebResourcePermission(String name, String actions)Creates a new WebResourcePermission with the specified name and actions. The name contains a URLPatternSpec that identifies the web resources to which the permissions applies. The syntax of a URLPatternSpec is as follows: URLPatternList ::= URLPattern | URLPatternList colon URLPattern URLPatternSpec ::= null | URLPattern | URLPattern colon URLPatternList A null URLPatternSpec is translated to the default URLPattern, "/", by the permission constructor. The empty string is an exact URLPattern, and may occur anywhere in a URLPatternSpec that an exact URLPattern may occur. The first URLPattern in a URLPatternSpec may be any of the pattern types, exact, path-prefix, extension, or default as defined in the Java Servlet Specification). When a URLPatternSpec includes a URLPatternList, the patterns of the URLPatternList identify the resources to which the permission does NOT apply and depend on the pattern type and value of the first pattern as follows: No pattern may exist in the URLPatternList that matches the first pattern. If the first pattern is a path-prefix pattern, only exact patterns matched by the first pattern and path-prefix patterns matched by, but different from, the first pattern may occur in the URLPatternList. If the first pattern is an extension pattern, only exact patterns that are matched by the first pattern and path-prefix patterns may occur in the URLPatternList. If the first pattern is the default pattern, "/", any pattern except the default pattern may occur in the URLPatternList. If the first pattern is an exact pattern a URLPatternList must not be present in the URLPatternSpec. The actions parameter contains a comma seperated list of HTTP methods. The syntax of the actions parameter is defined as follows: ExtensionMethod ::= any token as defined by RFC 2616 (that is, 1*[any CHAR except CTLs or separators]) HTTPMethod ::= "GET" | "POST" | "PUT" | "DELETE" | "HEAD" | "OPTIONS" | "TRACE" | ExtensionMethod HTTPMethodList ::= HTTPMethod | HTTPMethodList comma HTTPMethod HTTPMethodExceptionList ::= exclaimationPoint HTTPMethodList HTTPMethodSpec ::= null | HTTPMethodExceptionList | HTTPMethodList If duplicates occur in the HTTPMethodSpec they must be eliminated by the permission constructor. A null or empty string HTTPMethodSpec indicates that the permission applies to all HTTP methods at the resources identified by the URL pattern. If the HTTPMethodSpec contains an HTTPMethodExceptionList (i.e., it begins with an exclaimationPoint), the permission pertains to all methods except those occuring in the exception list. Parameters:name - the URLPatternSpec that identifies the application specific web resources to which the permission pertains. All URLPatterns in the URLPatternSpec are relative to the context path of the deployed web application module, and the same URLPattern must not occur more than once in a URLPatternSpec. A null URLPatternSpec is translated to the default URLPattern, "/", by the permission constructor. All colons occuring within the URLPattern elements of the URLPatternSpec must be represented in escaped encoding as defined in RFC 2396. actions - identifies the HTTP methods to which the permission pertains. If the value passed through this parameter is null or the empty string, then the permission pertains to all the possible HTTP methods.WebResourcePermissionpublic WebResourcePermission(String urlPatternSpec, String[] HTTPMethods)Creates a new WebResourcePermission with name corresponding to the URLPatternSpec, and actions composed from the array of HTTP methods. Parameters:urlPatternSpec - the URLPatternSpec that identifies the application specific web resources to which the permission pertains. All URLPatterns in the URLPatternSpec are relative to the context path of the deployed web application module, and the same URLPattern must not occur more than once in a URLPatternSpec. A null URLPatternSpec is translated to the default URLPattern, "/", by the permission constructor. All colons occuring within the URLPattern elements of the URLPatternSpec must be represented in escaped encoding as defined in RFC 2396. HTTPMethods - an array of strings each element of which contains the value of an HTTP method. If the value passed through this parameter is null or is an array with no elements, then the permission pertains to all the possible HTTP methods.WebResourcePermissionpublic WebResourcePermission(HttpServletRequest request)Creates a new WebResourcePermission from the HttpServletRequest object. Parameters:request - the HttpServletRequest object corresponding to the Servlet operation to which the permission pertains. The permission name is the substring of the requestURI (HttpServletRequest.getRequestURI()) that begins after the contextPath (HttpServletRequest.getContextPath()). When the substring operation yields the string "/", the permission is constructed with the empty string as its name. The permission's actions field is obtained from HttpServletRequest.getMethod(). The constructor must transform all colon characters occuring in the name to escaped encoding as defined in RFC 2396.Method Detailequalspublic boolean equals(Object o)Checks two WebResourcePermission objects for equality. WebResourcePermission objects are equivalent if their URLPatternSpec and (canonicalized) actions values are equivalent. The URLPatternSpec of a reference permission is equivalent to that of an argument permission if their first patterns are equivalent, and the patterns of the URLPatternList of the reference permission collectively match exactly the same set of patterns as are matched by the patterns of the URLPatternList of the argument permission. Two Permission objects, P1 and P2, are equivalent if and only if P1.implies(P2) && P2.implies(P1). Specified by:equals in class PermissionParameters:o - the WebResourcePermission object being tested for equality with this WebResourcePermission. Returns:true if the argument WebResourcePermission object is equivalent to this WebResourcePermission.getActionspublic String getActions()Returns a canonical String representation of the actions of this WebResourcePermission. In the canonical form, predefined methods preceed extension methods, and within each method classification the corresponding methods occur in ascending lexical order. There may be no duplicate HTTP methods in the canonical form, and the canonical form of the set of all HTTP methods is the value null. Specified by:getActions in class PermissionReturns:a String containing the canonicalized actions of this WebResourcePermission (or the null value).hashCodepublic int hashCode()Returns the hash code value for this WebResourcePermission. The properties of the returned hash code must be as follows: During the lifetime of a Java application, the hashCode method must return the same integer value, every time it is called on a WebResourcePermission object. The value returned by hashCode for a particular WebResourcePermission need not remain consistent from one execution of an application to another. If two WebResourcePermission objects are equal according to the equals method, then calling the hashCode method on each of the two Permission objects must produce the same integer result (within an application). Specified by:hashCode in class PermissionReturns:the integer hash code value for this object.impliespublic boolean implies(Permission permission)Determines if the argument Permission is "implied by" this WebResourcePermission. For this to be the case, all of the following must be true: The argument is an instanceof WebResourcePermission The first URLPattern in the name of the argument permission is matched by the first URLPattern in the name of this permission. The first URLPattern in the name of the argument permission is NOT matched by any URLPattern in the URLPatternList of the URLPatternSpec of this permission. If the first URLPattern in the name of the argument permission matches the first URLPattern in the URLPatternSpec of this permission, then every URLPattern in the URLPatternList of the URLPatternSpec of this permission is matched by a URLPattern in the URLPatternList of the argument permission. The HTTP methods represented by the actions of the argument permission are a subset of the HTTP methods represented by the actions of this permission. URLPattern matching is performed using the Servlet matching rules where two URL patterns match if they are related as follows: their pattern values are String equivalent, or this pattern is the path-prefix pattern "/*", or this pattern is a path-prefix pattern (that is, it starts with "/" and ends with "/*") and the argument pattern starts with the substring of this pattern, minus its last 2 characters, and the next character of the argument pattern, if there is one, is "/", or this pattern is an extension pattern (that is, it starts with "*.") and the argument pattern ends with this pattern, or the reference pattern is the special default pattern, "/", which matches all argument patterns. All of the comparisons described above are case sensitive. Specified by:implies in class PermissionParameters:permission - "this" WebResourcePermission is checked to see if it implies the argument permission. Returns:true if the specified permission is implied by this object, false if not.Skip navigation linksOverviewPackageClassUseTreeDeprecatedIndexHelpPrev ClassNext ClassFramesNo FramesAll ClassesSummary: Nested | Field | Constr | MethodDetail: Field | Constr | MethodCopyright 1996-2017, Oracle and/or its affiliates. All Rights Reserved. Use is subject to license terms. 006ab0faaa