设置类路径以便在mysql和jdbc之间进行连接 [英] set the classpath in order to connect between mysql to jdbc

问题描述

我使用的程序：eclipse和mysql。

我在mysql中有一个数据库，我想在eclipse和mysql之间建立连接。

我的项目中有一些我在日食中创建的文件夹。

我有主文件夹：testest ..和我告诉你我在相关文件夹中的内容：

  testest 
 ..src 
 .... testest 
 ...... testestservlet.java 
 ..app engine sdk 
 ..JRE系统库
 ..referenced library 
 ..war 
 ..lib 
 .... mysql-connector-java-5.1.22 
  

我更新了我的testestservlet.java：

  package testest; 
 
 import java.io.IOException; 
 import javax.servlet.http。*; 
 import java.sql。*; 
 
 @SuppressWarnings（serial）
公共类TestestServlet扩展HttpServlet {
 public void doGet（HttpServletRequest req，HttpServletResponse resp）
抛出IOException {
 resp.setContentType（ text / plain的）; 
 resp.getWriter（）。println（嘿，世界）; 
 resp.getWriter（）。println（MySQL Connect Example。）; 
连接conn = null; 
 String url =jdbc：mysql：// localhost：3306 /; 
 String dbName =database_alon; 
 String driver =com.mysql.jdbc.Driver; 
字符串userName =root; 
 String password =ADMINALON; 
 try {
 Class.forName（driver）.newInstance（）; 
 conn = DriverManager.getConnection（url + dbName，userName，password）; 
 resp.getWriter（）。println（连接到数据库）; 
 conn.close（）; 
 resp.getWriter（）。println（与数据库断开连接）; 
} catch（例外e）{
 e.printStackTrace（）; 
} 
} 
} 
  

现在，我运行testest运行as-> web application。

输入url：localhost：8888

并且只能看到'你好'世界'。

我读到了这一点，看到我需要写命令：

 设置CLASSPATH =％CLASSPATH％; JAVA_HOME \lib; 
  

但我的CLASSPATH和JAVA_HOME的url-s应该是多少？我有以下文件夹：c：/ program_fils / java
和：c：/ Jconnector（类似的东西）。

Jconnector的文件夹包含一个文件夹：mysql-connector-java-5.1.22.jar

我试图通过eclipse将JAR添加到库中（右键单击testest-> properties-> Libraries - >添加外部jar-> mysql-connector-java-5.1.22-bin.jar：

ps，我的操作系统是windows 32bit。

解决方案

没有必要这样做

 设置CLASSPATH =％CLASSPATH ％; JAVA_HOME \ lib; 
  

只需添加 mysql-connector-java- 5.1.22-bin.jar：到 / WEB-INF / lib 目录。

< Eclipse>智能足以识别在 / WEB-INF / lib 下添加的.jar文件，并且应该包含在CLASSPATH中。

使用添加库添加库外部Jar 也应该有效但不是最佳做法。

在 / WEB-INF中删除.jar使用 .war


在外部部署Web应用程序时，/ lib 也可以正常工作

I use the programs: eclipse and mysql.

I have a database in mysql and I want to connect between the eclipse to the mysql.

I have some folders in my project that I created in the eclipse.

I have the main folder: testest.. and I show you what I have in the relevant folders:

testest
..src
....testest
......testestservlet.java
..app engine sdk
..JRE system library
..referenced library
..war
..lib
....mysql-connector-java-5.1.22

I updated my testestservlet.java:

package testest;

import java.io.IOException;
import javax.servlet.http.*;
import java.sql.*;

@SuppressWarnings("serial")
public class TestestServlet extends HttpServlet {
  public void doGet(HttpServletRequest req, HttpServletResponse resp)
        throws IOException {
      resp.setContentType("text/plain");
      resp.getWriter().println("Hey, world");
      resp.getWriter().println("MySQL Connect Example.");
      Connection conn = null;
      String url = "jdbc:mysql://localhost:3306/";
      String dbName = "database_alon";
      String driver = "com.mysql.jdbc.Driver";
      String userName = "root"; 
      String password = "ADMINALON";
      try {
          Class.forName(driver).newInstance();
          conn = DriverManager.getConnection(url+dbName,userName,password);
          resp.getWriter().println("Connected to the database");
          conn.close();
          resp.getWriter().println("Disconnected from database");
      } catch (Exception e) {
          e.printStackTrace(); 
      }
  }
}

now, I run testest by run as->web application.

enter the url: localhost:8888

and only see the 'hello world'.

I read about that and see that I need to write the command:

set CLASSPATH=%CLASSPATH%;JAVA_HOME\lib;

but what are the url-s of my CLASSPATH and JAVA_HOME should be? I have folders of: c:/program_fils/java and: c:/Jconnector (something like that).

the folder of Jconnector contains a file of: mysql-connector-java-5.1.22.jar

I tried to add the JAR into the libraries via the eclipse (right click on testest->properties->Libraries->add external jar->mysql-connector-java-5.1.22-bin.jar:

p.s, my operating system is windows 32bit.

解决方案

There is no need of doing

set CLASSPATH=%CLASSPATH%;JAVA_HOME\lib;

Just add mysql-connector-java-5.1.22-bin.jar: to /WEB-INF/lib directory.

Eclipse is smart enough to recognize .jar files added under /WEB-INF/lib and should include in the CLASSPATH.

Adding a library using "Add External Jar" should also work but its not best practice.

Dropping ".jar" inside /WEB-INF/lib will also work when you externally deploy your web apllication using .war

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