Some basic knowledge about java
J2ee
Full name Java 2 Enterprise Edition, an enterprise version of Java for enterprise application development.
J2se
The full name of Java 2 Standard Edition, the standard version of Java, is used for standard application development and is also the Java base version.
J2me
The full name of Java 2 Micro Edition, a micro version of Java, is used for embedded development of mobile phones, PDAs, etc. For mobile phone development, there is also a dedicated J2ME Wireless Toolkit free kit.
All in all, J2EE, J2SE, and J2ME are different services provided by Java for different usage categories, that is, different types of libraries are provided. J2EE (Java 2 Enterprise Edition) for enterprise applications, J2SE (Java 2 Standard Edition) for common PC applications, and J2ME (Java 2 Micro Edition) for embedded devices and consumer appliances.
After the Java 5.0 version, J2EE, J2SE, and J2ME were renamed to JAVAEE JAVASE JAVAME.
SDK
The full name of Software Develop Kit, software development kit, is used to help developers improve development efficiency. Various types of software development can have their own SDK. Windows has the Windows SDK, DirectX has the DirectX 9 SDK, and .NET development also has the Microsoft .NET Framework SDK. Of course, JAVA development also has its own Java SDK.
JDK
The full name of the Java development toolkit, equivalent to Java library functions, is a toolkit for compiling and running Java programs. It is the basis of all Java applications. All Java applications are built on top of this. It is a set of APIs, or some java class. As a Java development toolkit, JDK is mainly used to build applications, applets and components running on the Java platform. At present, the ORACLE official website introduces that the JDK is part of the SDK, and the JDK and the SDK are released together.
JRE
Full name Java Runtime Environment, Java runtime environment, which is the Java platform. All Java programs must be run under the JRE. The JDK tool is also a Java program and requires a JRE to run. In order to maintain the independence and integrity of the JDK, the JRE is also part of the installation during the JDK installation process. Therefore, the current ORACLE official website introduction, JRE is part of the JDK, if you do not want to develop, just want to run the JAVA program, the official website can be downloaded to a separate JRE package, but if you want to develop, you still need to install the above JDK.
JVM
Full name Java Virtual Machine, Java Virtual Machine, is part of the JRE. It is a fictional computer that is implemented by simulating various computer functions on an actual computer. The JVM has its own complete hardware architecture, such as processors, stacks, registers, etc., and has a corresponding instruction system. The most important feature of the Java language is running across platforms. The JVM is used to support operating system-independent and cross-platform.
Therefore, the JAVA virtual machine JVM belongs to the JRE, and now we also install the JRE when installing the JDK (of course, you can also install the JRE separately).
Serverlet
A servlet is a java program that is executed on the server side, which can process user requests and respond to them. Of course, running such a java program requires serverlet container (eg, tomcat) support.
JSP
JSP (Java Server Pages) is a dynamic web technology standard advocated by Sun Microsystems and built by many companies. A Java program file (Scriptlet) and a JSP tag (tag) are inserted in a conventional web page HTML file (*.htm, *.html) to form a JSP file (*.jsp).
Simply put, jsp is an html file that may contain java program segments. In order to distinguish it from ordinary html, use jsp suffix name.
From jsp to serverlet to class, jsp is a certain server resource when it is first requested. Fortunately, this happens only once. Once the jsp file is translated and compiled into the corresponding servlet, it will be processed directly by the servlet when the next request comes.
The "Web server" in the above figure needs to have a jsp container (for example, tomcat) to be responsible for the interpretation of jsp. It is also because of this container that the Serverlet and class are generated.
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