The first is the download tool: It is recommended that beginners use EditPlus JDK, I think if I use, for example, JB, Eclipse, JCREATOR, although it is convenient to start, I don't know how to configure environment variables, so it is difficult to achieve it. Knowing what haills can be downloaded by the following address: editplus (the latest version is V2.11): http://count.skycn.com/softdown.php? Id = 3641 & url = http: //sc-http.skycn.net /down/EPP211A_CN.EXE (I want to find it yourself by the registration code, there are many online) JDK (the latest version is java2sdk1_4_2): http://count.skycn.com/softdown.php? id = 3116 & url = http: // SC-HTTP.SKYCN.NET/DOWN/J2SDK-1_4_2-windows-i586.exe (this is for Windows)
Then you install JDK, I put it below the C: / JDK directory: Then the ClassPath problem: Java running environment will also traverse classpath, even if the operating system uses PATH to search the executable. It is a simple program such as HelloWorld, and JVM will also traverse each path defined by classpath until the corresponding file is found. I believe that the system used is not 2K is XP, then set the path: My Computer -> Properties -> Advanced -> Environment Variables and add: C: / JDK / Bin ;; / JDK / lib can also be configured such: C: / JDK / BIN;; C: /JDK/LIB/dt.jar; c: /jdk/lib/tools.jar ★ Remember: Environment variables. Remember cannot Less, it represents the current path, if there is less error, etc.! Dt.jar is a class library about running the environment. Tools.jar is about the class library for some tools. If there is no configuration: C: / JDK / BIN, "Javac 'is not internal or external command, nor is it runable Or batch files. "This error. Then you will write the program below: First is (HelloWorld.java), open EditPlus, create a new Java file, please enter the following input, you want a word unlike, and select the case: public class helloworld {public static void main String [] args) {system.out.println ("Hello, World!");}} Then save this file (Ctrl S) to HelloWorld.java, remember the case must be divided, is helloworld.java is not HelloWorld.java or other below, start -> Run -> CMD Switch to the current directory in the console: Javac HelloWorld.javajava HelloWorld You will see the output of Hello, World! (no Come out? I take the computer :)) Javac is the compile command, which compiles helloWorld.java to HelloWorld.classjava is the explanation command, and JVM explains the HelloWorld.class. At this time: 1. If Exception in Thread "Main" java.lang.noclassdefounderror: HelloWorld is that you didn't add that in the environment variable. (Dot) 2. If an Exception in Thread "Main" java.lang.nosuchmethoder: main or helloWorld.java: main or helloworld.java: PUBLIC CLAS HELLOWORLD MUST BE Defined in a file caled "HelloWorld.java". That is, you didn't have a case write to this HelloWorld , Or keep it is not saved as helloworld.java, this name must be the same as the name of the public class.
When you have a problem with environmental variables, let's talk about how to compile and run in Editplus, in Tools-> Parameter Settings -> Configuring User Tools 1. Add Tools (Add Apps) Menu Text: Compile Java Program Programs : C: /jdk/bin/javac.exe Parameters: File Name Initial: File Directory 2. Add Tool (Add Application) Menu Text: Run Java Program Program: C: /jdk/bin/java.exe Parameters: File Name (excluding extension) Initial: File Directory Tools Group Name You can add, such as Debug Java Program, then in the Tools drop-down menu, you will see the two options of Compile Java Program and Run Java Program, you will You can use Ctrl 1 to compile and run the program.
Let's discuss the operation of servlet: First, you need to run the servlet, you need JSP / Servlet Container, I suggest that beginners use Tomcattomcat (latest version 5.0): http://cvs.apache.org/builds/jakarta-tomcat-5/nightly /jakarta-tomcat-5-bin-20030725.zip then extract this compressed package to: c: / tomcat and then configure environment variables: Add three system variables: java_home: c: / jdktomcat_home: c: / tomcatclasspath:% java_home % / lib;% Tomcat_Home% / libtomcat's environment variable is configured, check whether Tomcat can run: Go to C: / Tomcat / bin in the console, run startup, then return a window, join one Big string, finally said that Server has run in the browser to enter http: // localhost: 8080, the welcome interface, indicating that Tomcat has no problem, and writes your first servletimport java.io. *; import javax.servlet *;. import javax.servlet.http *;. public class HelloWorld extends HttpServlet {public void doGet (HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
Response.setContentType ("text / html"); printwriter out = response.getwriter (); out.println (""); out.println ("
Hello, World! ");
OUT.PRINTLN ("");
}
}
Then use Javac HelloWorld.java to compile this file, if there is an import javax.servlet. *
Then you should copy the servlet.jar file in C: / Tomcat / Common / Lib to C: / JDK / JRE / LIB / EXT, compile again, no problem!
Then in the C: / Tomcat / WebApps / root in the Tomcat directory, follow the following file structure: root / index.html
Root / welcom.jsp
Root / Web-INF / LIB / MyServlet.jar (if your servlet is piled up .jar file, put it under LIB)
Root / Web-INF / CLASS / HELLOWORLD.CLASS (put the helloWorld.class file generated above))
Then enter http: // localhost: 8080 / servlet / helloWorld in the browser, and the error is returned by the service: Error 404 - NOT FOUND What is going on? Servlet must use the web.xml file below the c: / tomcat / webapps / root / web-infront of the directory, open this web.xml file with EP, join inside
HelloWorld
HelloWorld
HelloWorld
/ servlet / helloworld
Such structure
HelloWorld
HelloWorld represents the specified servlet class. The following structure
HelloWorld
/ servlet / helloworld indicates which URL schema that specifies the Helloservlet to map. After modifying web.xml, restart Server, then enter http: // localhost: 8080 / servlet / helloWorld, then a Hello, World! Waiting for you, congratulations, you are flattening :) Ai, hands play Tired, write here, I hope to have a little role in beginners!
============================================================================================================================================================================================================= ========================= How to build a connection database app? For example, connect Access, and SQL Sever. I heard that there is a JDBC JDBC-ODBC bridge.
At present, only JDK1.4 on my machine, what environment I want to use with JDBC? If you want a JDBC driver, you can go down? And how do you write? -------------------------------------------------- ------------- If you use the drive bridge, you don't need another installation. Don't install anything in the control, the bridge -> Management Tools -> Data Source (ODBC) -> SystemDSN Add you Database mapping, select the corresponding database driver and then connect the database through the JDBC: ODBC: set the DSN name --------------------- ------------------------------------------ package cbk00d.common; / ** * Title: * Description: * Copyright: Copyright (c) 2001 * Company: * @Author * @version 1.0 * / import java.io. *; import java.util. *; Import java.sql. *; Import java. lang *;. public class DBConnect {private String jdbcDriver = null; private String jdbcURL = null; private String userName = null; private String password = null; public DBConnect () {jdbcDriver = "sun.jdbc.odbc.JdbcOdbcDriver"; jdbcURL = "JDBC: ODBC: CBK"; username = "system"; password = "manager";} public connection getConnec tion () {Connection connection = null; try {Class.forName (jdbcDriver); connection = DriverManager.getConnection (jdbcURL, userName, password);} catch (Exception e) {System.out.println (e);} return connection This is an ordinary connection method! Just modify it.
-------------------------------------------------- ------------- It seems like this, must be rs.next () JDBC-ODBC bridge is not good? ^ _ ^ Java connection database There are a variety of ways: according to the different database drivers required, divided into four: 1: 1 type driver. This is the way the JDBC-ODBC bridge. But this method is not suitable for reuse and maintenance of the program, not recommended. A database of ODBC drivers are required. 2: 2 type driver. This is the form of the JDBC manufacturer API. Vendor API usually uses C, so this approach is not long. 3: 3 type driver. This is the form of JDBC vendor Database Connection Server Database. This method is to have a server that is dedicated to database connections between Java and Database (generally provided by database vendors). His benefits are to optimize the connection. 4: Category 4 driver. This is the connection method of pure JDBC Database. It is also recommended to connect. This makes Application to the database, developers only need to care about internal logic without paying attention to specific implementations of database connections. There are two ways to connect in this: hard-coding mode is the necessary parameters that are hardly encapsulated in the database. JNDI DataSource method. That is to set a DataSource source in the outline environment of the program, there is a JNDI name, and the program only needs to find this name to get a database connection object.
