Java Learning Path (i), tools

The JDK (Java Development Kit) JDK is the core of the entire Java system, including the Java Runtime Environment (Java Runtime envirnment), a stack of Java tools and a Java-based class library (Rt.jar). No matter what Java application Server is in essence a version of the JDK is built in. So mastering the JDK is the first step in learning java. The most mainstream JDK is the JDK that Sun releases, and many companies and organizations, in addition to Sun, have developed their own JDK, such as the Jrocket of IBM's Jdk,bea company, the JDK developed by the GNU organization, and so on. IBM's JDK contains JVM (Java Virtual Machine) that is much more efficient than the JVM contained in the Sun JDK. The Jrocket, which runs on the x86 platform, is also much better at the server than the Sun JDK. But anyway, we need to get the sun JDK first.


1, JDK download and install JDK, also known as J2SE (Java2 SDK Standard Edition), can be downloaded from the Sun's Java Web site, http://java.sun.com/j2se/downloads.html, The current version of the JDK is j2sdk1.4.2, and it is recommended that you download this version of the JDK, download the page here: http://java.sun.com/j2se/1.4.2/download.html. The downloaded JDK is an executable installer that installs a set of JRE (for browsers to use) under the C:\Program files\java\ directory after the default installation, and installs a set of JDK (also includes a JRE) under C:\j2sdk1.4.2. Then we need to add the Java path C:\j2sdk1.4.2\bin to the front of the environment variable path. So the JDK is installed.


2, JDK's command tool JDK's most important command-line tools: Java: Start JVM execution Class Javac:java compiler Jar:java Packaging tools Javadoc:java Document Builder These command lines must be very, very familiar, and for each parameter Proficiency is the only line. For the learning of these commands, the JDK documentation has detailed documentation.





Two, JDK documentation documentation in the JDK download page also has the download connection, the proposal simultaneously downloads the documentation. Documentation is the most important programming manual, covering all aspects of the entire Java description of the content. It can be said that learning Java programming, most of the time is spent looking at the documentation above. I was carrying, write Java code, at any time to view, a moment of the hand.





III, Application Server (app server) app servers are platforms that run Java Enterprise components, which constitute the main operating environment of the application software. The current mainstream app server is Bea's WebLogic server and IBM's WebSphere and free JBoss, choose one to learn from, and personally recommend WebLogic, because its architecture is cleaner, Development and deployment is more convenient, is the Java enterprise Software developers preferred development platform. The following is a brief introduction to several commonly used app servers:


1, Tomcat Tomcat is strictly not a real app server, it's just a web container that can support running serlvet/jsp, but Tomcat also extends some of the functionality of the app server, such as Jndi, database connection pool, User transaction processing, and so on. Tomcat is very widely used in small and medium sized Java Web applications, so this article does a little bit of downloading, installing, and configuring Tomcat: Tomcat is a subproject under the Apache Jakarta Project, and its main web site is: http:// jakarta.apache.org/tomcat/, the latest version of Tomcat is Tomcat4.1.27, the software download connection is: http://www.apache.org/dist/jakarta/tomcat-4/ Binaries/. Tomcat can download either the ZIP package directly, or the EXE installation package (personal suggestion zip cleaner), in either case, after the download is installed (Zip Direct decompression can be.) Two environment variables need to be set: java_home=c:\j2sdk1.4.2 catalina_home=d:\tomcat4 (your Tomcat installation directory) so it's installed, start Tomcat running catalina_home\bin\ Startup.bat, turn off Tomcat run Shutdown.bat script. After Tomcat is started, the 8080 port is used by default, so you can use the browser to access http://localhost:8080 to test whether Tomcat starts properly. Tomcat provides management tools for two web interfaces, the URL being: http://localhost:8080/admin/index.jsp http://localhost:8080/manager/html Before enabling these two administrative tools, you need to manually configure the administrator user and password. Open Catalina_home\conf\tomcat-users.xml This file with a text tool and add the following lines: <role rolename= "manager"/> <role rolename= "admin "/> <user username=" Robbin password= "12345678" roles= "Admin,manager,tomcat"/> so that the user "Robbin" has Super Administrator privileges. RebootAfter Tomcat, you can use the user to log on to the two admin tools on the Web for Tomcat configuration and management.


2, Bea Weblogic Weblogic can go to Bea's website for free registration after downloading to the latest Weblogic8.1 Enterprise Edition, license can use 1 years of free time, in fact, this is completely enough. WebLogic Download Connection: http://commerce.bea.com/index.jsp,.../edocs.bea.com/.


3, IBM Webshpere WebSphere can also download to the free trial version, to IBM's Developerworks Web site can see the WebSphere Trial product downloads and related WebSphere information, DeveloperWorks Chinese web site connection is: http://www-900.ibm.com/developerWorks/cn/wsdd/, WebSphere download connection: http:// Www7b.software.ibm.com/wsdd/... Wassupport.html.


4, JBoss JBoss is a free and open source app Server that can be downloaded free from the JBoss Web site: http://www.jboss.org/index.html, ... n.com/idea.html





Four, Java application of the operating environment Java application can be easily divided into the following aspects:


1, Java desktop application desktop applications generally require only the support of the JRE is sufficient.


2, Java Web application Java Web applications need to install at least JDK and a web container (such as Tomcat), as well as a multiuser database, Web applications are divided into at least three layers: Browser layer: Browser display user page Web layer: Run servlet/ JSP DB layer: Back-end database, providing data access services to Java programs


3, Java Enterprise Application Enterprise application is more complex, can be extended to n-tier, the simplest case will be divided into 4 layers: Browser layer: Browser display user page client layer: Java Client graphics program (or embedded device program) directly with the Web layer or the EJB layer interaction Web layer: Run servlet/jsp EJB layer: Run EJB, complete business logic Operation DB Layer: Back-end database, provide data access service to Java program


4, Java embedded application Java Embedded application is a burgeoning field, engaged in embedded development, need to download from the Sun J2ME development package, J2ME contains the embedded device dedicated virtual machine KVM, and the common JDK included in the JVM is different. There is also a need to download the simulator to a specific embedded vendor.