Misplaced Pages

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38-591: A Jakarta Servlet is a Java class in Jakarta EE that conforms to the Jakarta Servlet API, a standard for implementing Java classes that respond to requests. Servlets could in principle communicate over any client–server protocol, but they are most often used with HTTP . In principle, any servlets can extend the GenericServlet class; however, realistically speaking, all servlets extend

76-486: A Model 2 application, requests from the client browser are passed to the controller . The controller performs any logic necessary to obtain the correct content for display. It then places the content in the request (commonly in the form of a JavaBean or POJO ) and decides which view it will pass the request to. The view then renders the content passed by the controller. Model 2 is recommended for medium- and large-sized applications. In 1998, Sun Microsystems published

114-514: A pre-release of the JavaServer Pages specification, version 0.92. In this specification, Sun laid out two methods by which JSP pages could be used. The first model (referred to as " model 1 " due to its ordering in the document) was a simplistic model whereby JSP pages were standalone, disjointed entities. Logic could be contained within the page itself, and navigation between pages was typically achieved by way of hyperlinks. This fit with

152-535: A product until December 1996 when Sun shipped JWS. This was before what is now the Jakarta EE was made into a specification. The Servlet1 specification was created by Pavni Diwanji while she worked at Sun Microsystems , with version 1.0 finalized in June 1997. Starting with version 2.2, the specification was developed under the Java Community Process . Three methods are central to the life cycle of

190-406: A servlet and using URL mapping with a servlet. Before servlet 3.0 specification (Tomcat 7.0), configuring the web.xml to map a servlet to a URL was the only option. For applications using the servlet 3.0 specification or later, the @WebServlet annotation can be used to map any servlet to one or more URL patterns. Servlets may be packaged in a WAR file as a web application . A web container

228-545: A servlet. These are init() , service() , and destroy() . They are implemented by every servlet and are invoked at specific times by the server. The following is a typical user scenario of these methods. The following example servlet prints how many times its service() method was called. Note that HttpServlet is a subclass of GenericServlet , an implementation of the Servlet interface. The service() method of HttpServlet class dispatches requests to

266-440: A struct, the code below won't compile and only serves as a demonstration. The constant pool table is where most of the literal constant values are stored. This includes values such as numbers of all sorts, strings, identifier names, references to classes and methods, and type descriptors. All indexes, or references, to specific constants in the constant pool table are given by 16-bit (type u2) numbers, where index value 1 refers to

304-492: Is a file (with the .class filename extension ) containing Java bytecode that can be executed on the Java Virtual Machine (JVM) . A Java class file is usually produced by a Java compiler from Java programming language source files ( .java files) containing Java classes (alternatively, other JVM languages can also be used to create class files). If a source file has more than one class, each class

342-435: Is a field_info structure defined in https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.5 each element is a method_info structure defined in https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.6 each element is an attribute_info structure defined in https://docs.oracle.com/javase/specs/jvms/se8/html/jvms-4.html#jvms-4.7 Since C doesn't support multiple variable length arrays within

380-449: Is an object that receives a request and generates a response based on that request. The basic Servlet package defines Java objects to represent servlet requests and responses, as well as objects to reflect the servlet's configuration parameters and execution environment. The Servlet API , contained in the Java package hierarchy javax.servlet , defines the expected interactions of

418-448: Is compiled into a separate class file. Thus, it is called a .class file because it contains the bytecode for a single class. JVMs are available for many platforms , and a class file compiled on one platform will execute on a JVM of another platform. This makes Java applications platform-independent . On 11 December 2006, the class file format was modified under Java Specification Request (JSR) 202. There are 10 basic sections to

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456-986: Is no enforcement of word alignment, and so no padding bytes are ever used. The overall layout of the class file is as shown in the following table. Java SE 24 = 68 (0x44 hex), Java SE 23 = 67 (0x43 hex), Java SE 22 = 66 (0x42 hex), Java SE 21 = 65 (0x41 hex), Java SE 20 = 64 (0x40 hex), Java SE 19 = 63 (0x3F hex), Java SE 18 = 62 (0x3E hex), Java SE 17 = 61 (0x3D hex), Java SE 16 = 60 (0x3C hex), Java SE 15 = 59 (0x3B hex), Java SE 14 = 58 (0x3A hex), Java SE 13 = 57 (0x39 hex), Java SE 12 = 56 (0x38 hex), Java SE 11 = 55 (0x37 hex), Java SE 10 = 54 (0x36 hex), Java SE 9 = 53 (0x35 hex), Java SE 8 = 52 (0x34 hex), Java SE 7 = 51 (0x33 hex), Java SE 6.0 = 50 (0x32 hex), Java SE 5.0 = 49 (0x31 hex), JDK 1.4 = 48 (0x30 hex), JDK 1.3 = 47 (0x2F hex), JDK 1.2 = 46 (0x2E hex), JDK 1.1 = 45 (0x2D hex). For details of earlier version numbers see footnote 1 at The JavaTM Virtual Machine Specification 2nd edition each element

494-566: Is only responsible for processing, and the JSP is only responsible for presenting the HTML, allowing for a clear separation of concerns and conformance to the single-responsibility principle . While the direct usage of servlets to generate HTML (as shown in the example below) has become rare, the higher level MVC web framework in Jakarta EE ( Faces ) still explicitly uses the servlet technology for

532-485: Is required for deploying and running a servlet. A web container (also known as a servlet container) is essentially the component of a web server that interacts with the servlets. The web container is responsible for managing the lifecycle of servlets, mapping a URL to a particular servlet and ensuring that the URL requester has the correct access rights. Servlets can be generated automatically from Jakarta Server Pages (JSP) by

570-482: The HttpServlet class. Thus "servlet" is often used as shorthand for "HTTP servlet". Thus, a servlet can be used to add dynamic content to a web server using the Java platform . The generated content is commonly HTML , but may be other data such as XML and more commonly, JSON . The Jakarta Servlet API has, to some extent, been superseded by two standard Java technologies for web services: A Servlet

608-520: The Jakarta Server Pages compiler . The difference between servlets and JSP is that servlets typically embed HTML inside Java code, while JSPs embed Java code in HTML. In general, when using JSPs, embedding Java code in JSP is considered bad practice. Instead, a better approach would be to move the back-end logic from the JSP to the Java code in the Servlet . This ensures that the Servlet

646-461: The "Model 2" pattern. Once again, the implementation of the "Model" was left undefined with the expectation that software developers would fill in an appropriate solution. Database interaction via JDBC and EJBs were options suggested on the Struts homepage. More recently, Hibernate , iBatis , and Object Relational Bridge were listed as more modern options that could be used for a model. Since

684-570: The "View" and the "Controller" (respectively) in an MVC architecture. The "Model" part of the MVC architecture was left open by Govind, with a suggestion that nearly any data-structure could meet the requirements. The specific example used in the article was a Vector list stored in the user's session. In March 2000, the Apache Struts project was released. This project formalized the division between View and Controller and claimed implementation of

722-567: The Java BluePrints specifically warn against this interpretation: The literature on Web-tier technology in the J2EE platform frequently uses the terms "Model 1" and "Model 2" without explanation. This terminology stems from early drafts of the JSP specification, which described two basic usage patterns for JSP pages. While the terms have disappeared from the specification document, they remain in common use. Model 1 and Model 2 simply refer to

760-587: The Java class file structure: Class files are identified by the following 4 byte header (in hexadecimal ): CA FE BA BE (the first 4 entries in the table below). The history of this magic number was explained by James Gosling referring to a restaurant in Palo Alto : "We used to go to lunch at a place called St Michael's Alley. According to local legend, in the deep dark past, the Grateful Dead used to perform there before they made it big. It

798-606: The Unicode standard, although it is similar. There are two differences (see UTF-8 for a complete discussion). The first is that the code point U+0000 is encoded as the two-byte sequence C0 80 (in hex) instead of the standard single-byte encoding 00 . The second difference is that supplementary characters (those outside the BMP at U+10000 and above) are encoded using a surrogate-pair construction similar to UTF-16 rather than being directly encoded using UTF-8. In this case each of

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836-428: The absence or presence (respectively) of a controller servlet that dispatches requests from the client tier and selects views. Furthermore, the term "MVC2" has led many to a mistaken belief that Model 2 represents a next-generation MVC pattern. In fact, MVC2 is simply a shortening of the term "MVC Model 2". The confusion over the term "MVC2" has led to additional confusion over Model 1 code, resulting in common usage of

874-607: The content to render into a request attribute (typically represented by a JavaBean), then call a JSP to render the content in the desired output format. This model differed from the previous model in the fact that JSP technology was used as a pure template engine. All of the logic was separated out into a servlet, leaving the JSP with the sole responsibility of rendering the output for the content provided. In December 1999, JavaWorld published an article by Govind Seshadri entitled Understanding JavaServer Pages Model 2 architecture . In this article, Govind accomplished two major milestones in

912-527: The content. Since Model 2 drives a separation between logic and display, it is usually associated with the model–view–controller (MVC) paradigm. While the exact form of the MVC "Model" was never specified by the Model 2 design, a number of publications recommend a formalized layer to contain MVC Model code. The Java BluePrints , for example, originally recommended using EJBs to encapsulate the MVC Model. In

950-483: The first constant in the table (index value 0 is invalid). Due to historic choices made during the file format development, the number of constants in the constant pool table is not actually the same as the constant pool count which precedes the table. First, the table is indexed starting at 1 (rather than 0), but the count should actually be interpreted as the maximum index plus one. Additionally, two types of constants (longs and doubles) take up two consecutive slots in

988-442: The high-level language, such as boolean, byte, and short must be represented as an integer constant. Class names in Java, when fully qualified, are traditionally dot-separated, such as "java.lang.Object". However within the low-level Class reference constants, an internal form appears which uses slashes instead, such as "java/lang/Object". The Unicode strings, despite the moniker "UTF-8 string", are not actually encoded according to

1026-521: The low level request/response handling via the FacesServlet . A somewhat older usage is to use servlets in conjunction with JSPs in a pattern called " Model 2 ", which is a flavor of the model–view–controller . The Java Servlet API was first publicly announced at the inaugural JavaOne conference in May 1996. About two months after the announcements at the conference, the first public implementation

1064-554: The methods doGet() , doPost() , doPut() , doDelete() , and so on; according to the HTTP request. In the example below service() is overridden and does not distinguish which HTTP request method it serves. The specification for Servlet technology has been implemented in many products. See a list of implementations on the web container page. There are also other types of servlet containers such as those for SIP servlets, e.g., SailFin . Java class A Java class file

1102-420: The object file format, and in grepping for 4 character hex words that fit after "CAFE" (it seemed to be a good theme) I hit on BABE and decided to use it. At that time, it didn't seem terribly important or destined to go anywhere but the trash-can of history. So CAFEBABE became the class file format, and CAFEDEAD was the persistent object format. But the persistent object facility went away, and along with it went

1140-403: The release of Struts, a number of competing frameworks have appeared. Many of these frameworks also claim to implement "Model 2" and "MVC". In result, the two terms have become synonymous in the minds of developers. This has led to the use of the term "MVC Model 2" or "MVC2" for short. A common misconception is that a formalized MVC pattern is required to achieve a Model 2 implementation. However,

1178-439: The table, although the second such slot is a phantom index that is never directly used. The type of each item (constant) in the constant pool is identified by an initial byte tag . The number of bytes following this tag and their interpretation are then dependent upon the tag value. The valid constant types and their tag values are: There are only two integral constant types, integer and long. Other integral types appearing in

Jakarta Servlet - Misplaced Pages Continue

1216-401: The then-common usage of template technology. ColdFusion and Active Server Pages are examples of contemporary technologies that also implemented this model. The second model referred to by the document ("model 2" in the ordering) was an improved method that combined servlet technology with JSP technology. The specific difference listed was that a servlet would intercept the request, place

1254-459: The two surrogates is encoded separately in UTF-8. For example, U+1D11E is encoded as the 6-byte sequence ED A0 B4 ED B4 9E , rather than the correct 4-byte UTF-8 encoding of F0 9D 84 9E . JSP model 2 architecture JSP Model 2 is a complex design pattern used in the design of Java Web applications which separates the display of content from the logic used to obtain and manipulate

1292-496: The use of CAFEDEAD - it was eventually replaced by RMI ." Because the class file contains variable-sized items and does not also contain embedded file offsets (or pointers), it is typically parsed sequentially, from the first byte toward the end. At the lowest level the file format is described in terms of a few fundamental data types: Some of these fundamental types are then re-interpreted as higher-level values (such as strings or floating-point numbers), depending on context. There

1330-408: The use of the term "Model 2". The first milestone was to formalize the term "Model 2" as an architectural pattern rather than one of two possible options. The second milestone was the claim that Model 2 provided an MVC architecture for web-based software. Govind believed that because "Model 2" architecture separated the logic out of the JSP and placed it in a servlet, the two pieces could be seen as

1368-488: The web container and a servlet. The package javax.servlet.http defines HTTP -specific subclasses of the GenericServlet . This package includes session management objects that track multiple requests and responses between the web server and a client. Servlets can maintain state in session variables across many server transactions by using HTTP cookies , or URL mapping . There are several ways of creating

1406-435: Was a pretty funky place that was definitely a Grateful Dead Kinda Place. When Jerry died, they even put up a little Buddhist-esque shrine. When we used to go there, we referred to the place as Cafe Dead. Somewhere along the line it was noticed that this was a HEX number. I was re-vamping some file format code and needed a couple of magic numbers : one for the persistent object file, and one for classes. I used CAFEDEAD for

1444-539: Was made available on the JavaSoft website. This was the first alpha of the Java Web Server (JWS; then known by its codename Jeeves ) which would eventually be shipped as a product on June 5, 1997. In his blog on java.net , Sun veteran and GlassFish lead Jim Driscoll details the history of servlet technology. James Gosling first thought of servlets in the early days of Java , but the concept did not become

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