What is java? Why java?
Everything you have learned from Java, basically Java is a better object-oriented language, API rich
It is the current comparative mainstream programming language, J2SE / J2ME / J2EE has developed well in various development fields.
Java will not replace other development languages or development platforms, such as C / C / C # or Delphi / .NET
Without the best language, there is only a relatively suitable language under certain applications.
JRE
Java 2 Runtime Environment, Java runtime environment
Includes Java Virtual Machine (JVM), and must-have libraries
It is a must-have environment running Java programs and web applets
It is included in J2SDK or downloaded separately (about 10m)
download link:
http://java.sun.com/getjava/download.html
JDK / SDK / J2SE
Java 2 Software Development Kit, Standard EDTION
It is an essential environment for developing Java, including tools such as compilers and a large number of libraries, and they will also bring them in general IDE.
download link:
http://java.sun.com/j2se/downloads.html
J2EE
Java 2 Platform, Enterprise Edition
It is the main technology of Java in enterprise applications, and it is also the most important application in Java.
Including JAXP, JAXR, JAX-RPC, Saaj, Jaas, JavaMail, JMS, JSF, JSP / Servlet, etc.
Develop J2EE, you can download the J2EESDK development package, and you will also bring it in general IDE.
Related Links:
http://java.sun.com/j2ee
J2ME
Java 2 Platform, Macro Edition
It is the main technique for Java applications to embedded systems (such as mobile phones)
Related Links:
http://java.sun.com/J2ME
Development method
The IDE (integrated development environment) on the market can greatly improve the development efficiency
But if you begin a Java, we recommend JDK EditPlus or UltraEdit
Although it is very simple, it can learn more solid
Premature dependence IDE will only let you give a little water, a semi-solving.
Even unable to master the basic syntax of Java
After mastering a solid foundation, it is easy to choose an IDE for development.
Learning or using Java, more Javadoc is very important (recommended using javadochelper, similar to MSDN interface)
Many problems in the version, in fact, slightly book is not a problem
Set an environment variable
After installing JDK, configure environment variables
WINDOWS 2000
My Computer -> Properties -> Advanced -> Environmental Variables
Add the following environment variables (assuming your Java installed in d: /java/j2sdk1.4.2)
Variable name value
Java_Home D: /java/j2sdk1.4.2
Represents the current directory, search the current directory
PATH ...;% java_home% / bin ... Represents the original PATH value
New open a DOS window, type Java and Javac test
Linux
The following is the redhat, Bash is slightly different, and the settings of the environment variable are available in the UNIX / Linux version.
Modify the .bash_profile in the user directory, such as vi ~ / .bash_profile
Java_home = / usr / local / java / j2sdk1.4.2
Classpath =.
PATH = $ PATH: $ java_home / bin
Export Java_Home ClassPath
Re-login, make this setting take effect, enter the Java Javac test on the terminal to test a simple test program
Code: --------------------------------
Public class test {
Public static void main (String [] args) {
System.out.println ("Hello World!");
}
}
-------------------------------------
Write with Tools such as Notepad, save it into test.java
note,
If your Windows setup 'does not show a known extension',
It is very likely to be saved into test.java.txt
Then in the command line tool, CD to Test.java, execute
Javac Test.java
Java Test
About Java learning
Getting started with Java, please see a system to explain Java books.
Book in this area, there are many markets in the market, the same size is different, and it doesn't matter.
But try to pick a book that speaks the grammar for high versions, don't choose "VJ Getting Started to Jing".
Recommended books such as Java in a nutshell, Java University tutorial, Java core technology, Java programming ideas, etc.
System learning Java's basic knowledge, must have practical practice, give yourself some to do some opportunities
Moderately remember some common API, do not over-reliance on the IDE code prompt
development tools
JBuilder
One of the most mainstream IDEs in the industry is the big brother of Java development tools.
The latest version of JBuilder 2005
Regardless of the development J2SE, J2ME, J2EE or XML / WebService is a tool
Foundation Edition can be downloaded for free, but less functionality
There is a circular version of the Internet, in order to avoid unnecessary trouble, please use carefully (especially in the company)
Related Links:
http://www.borland.com/products/jbuilder
Eclipse
Emerging Java IDE, free, open source, cross-platform, powerful, fast running speed
At the same time, you can extend the functionality of existing plugins by developing new plugins, such as adding in an existing Java development environment.
Enter the Tomcat server plugin.
Related Links:
http://www.eclipse.org
Ant
It is popular Java Build tool, "Everyone Should Use Ant"
Ant is not an IDE, but you can do a lot of IDE, such as compilation / packaging / deployment / unit test / CVS, etc.
For projects above medium-size, it must rely on many class libraries and have complex bag structures.
Treatment with Ant is excellent choice
Related Links:
http://ant.apache.org
JSP
Java Server Page, a technology for Java web development, and JavaScript has no relationship.
Servlet
Dynamic web technology appeared in JSP, similar to CGI, but using multi-threaded process requests.
JSP / Servlet and Java relationship
Servlet just inherits the Httpservlet's Java class, and JSP will eventually be compiled into servlet and execute.
Many problems encountered when developing Web, in fact, and JSP / servlet itself has no relationship, but ordinary Java asked
question. A qualified JSP / servlet programmer should first be qualified Java programmers.
It is recommended to take a solid Java foundation before learning and using JSP / servlet.
The following questions are not part of JSP / Servlet
Using the use of API, such as "How to get the int" How to get Current Time "" How to create thread "
. JDBC use and related precautions, such as "how to access mysql" "Why do I insert data is garbled". Other J2EE technology use, such as "How to use JavaMail" "How to Access EJB"
Recommended books
If possible, please read a system book to guide you to learn this technology.
I only have seen "JSP Advanced Programming" (Machinery Industry 2001, Liao Ruoxue)
The books published in other large publishers should be good, such as Wrox, O'Reilly, or domestic publishing house
When you choose a book, you should use JSP 1.2, servlet 2.3 specification or above.
Tomcat
This is an open source JSP / servlet server, which is a reference implementation of JSP / Servlet, suitable for beginners.
Homepage
Http://jakarta.apache.org/tomcat/
Tomcat 4.1 and Tomcat 5 are currently stable versions, the latter supports the latest JSP / Servlet standard
It is recommended to download the Zip version, decompress, run bin / starup.bat, you can display the server startup
If the startup fails, make sure that the Java environment of this machine is correct, see Java_Home and Path configuration
In the confed directory, the server is configured. WebApps is a directory for deploying websites.
Where should I write from the Java Class written?
Suppose your index.jsp location is x: /test/index.jsp, x: / test is your project directory
Test.class location should be x: /test/web-inf/classes/test.class
Where should liblic?
X: /test/web-inf/lib/mylib.jar
How to write a servlet
Package testservlet;
Import java.io. *;
Import javax.servlet.servletException;
Import javax.servlet.http. *;
Public class fooservlet extends httpservlet {
Protected Void Doget (HTTPSERVLETREQUEST REQ, HTTPSERVLETRESPONSE RESP)
Throws servletexception, ioException {
Resp.Getwriter (). Println ("Hi, I'm a servlet);
}
}
Compiled this Javac-ClassPath Servlet-Api.jar Fooservlet.java
Among them, this JAR can get from Tomcat-5.0.19 / Common / lib / servlet-api.jar
Compiled Class in x: /test/web-inf/classes/testServlet/fooservlet.class
Among them, TestServlet your name, you should try to write package, avoid inexplicably troublesome
Compile x: /test/web-inf/web.xml, modified
2.3 // en ""
http://java.sun.com/dtd/web-app_2_3.dtd ">
Deploy this program to the server, such as copying x: / test / * to Tomcat / WebApps / Test / *
Open browser access
Http: // localhost: 8080 / test / foobar, will see a line of words smoothly
JSP shows what is garbled?
JSP's Chinese issues // do not include Chinese issues for JDBC read and write databases
1. The Chinese written in the JSP, such as
Chinese , but cannot be displayed
Solution to join the first line of JSP
<% @ Page ContentType = "text / html; charset = GB2312"%>
2. A Chinese is written in the form, such as
But you can't accept <% system.out.println (Request.GetParameter ("a"));%>
Solution to add one before processing parameters in JSP or Servlet
Request.SetCharacterencoding ("GB2312");
3.
http://host/a.jsp? Name = Name in the URL in Chinese is not available
Workaround should use the java.net.urlencoder class to turn this string to ASCII
How to achieve file upload
Common Java file upload API has
Jakarta Commons Fileupload
http://jakarta.apache.org/commons/fileupload/
COS
Smartupload
Download related files, usually Demo
JSTL and EL
Java Standard Tag LIB and Expression Language, respectively, respectively
It can greatly simplify the regular JSP development and make the page more concise, rather than full of Scriptlet
