How to install JDBC driver in Eclipse web project without facing java.lang.ClassNotFoundexception

问题

There is a VERY similar question to mine but in my case I don't have any duplicate jars in my build path, so the solution does not work for me. I've searched google for a couple of hours now, but none of the solutions I've found there actually resolve my issue. I'm creating a web site with some database connectivity for a homework. I'm using a MySQL database, developing in Eclipse and running on Windows.

I keep getting java.lang.ClassNotFoundException: com.mysql.jdbc.Driver with the following code:

import java.sql.*;
//...
public void someMethodInMyServlet(PrintWriter out)
{
    Connection connection = null;
    PreparedStatement query = null;
    try {

        out.println("Create the driver instance.<br>");
        Class.forName("com.mysql.jdbc.Driver").newInstance();

        out.println("Get the connection.<br>");
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "secret");
        query = connection.prepareStatement( "SELECT * FROM customers");

        //...
    } catch (Exception e)
    {
        out.println(e.toString()+"<br>");
    }
}
//...

When I run the above code I get the following output:

Create the driver instance.
java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

It doesn't get past the Class.forName... line and I can't figure out why! Here is what I did:

Download mysql-connector.
Put it in my MySQL folder C:\Program Files\MySQL\mysql-connector-java-5.1.12\mysql-connector-java-5.1.12-bin.jar.
Opened the project properties in Eclipse.
Add External Jar to my Build Path and I selected mysql-connector-java-5.1.12-bin.jar.

Every time I attempt to use the servlet I get the same error regardless if I have the jar in there or if I don't. Could you help me figure this out?

回答1:

As for every "3rd-party" library in flavor of a JAR file which is to be used by the webapp, just copy/drop the physical JAR file in webapp's /WEB-INF/lib. It will then be available in webapp's default classpath. Also, Eclipse is smart enough to notice that. No need to hassle with buildpath. However, make sure to remove all unnecessary references you added before, else it might collide.

An alternative is to install it in the server itself by dropping the physical JAR file in server's own /lib folder. This is required when you're using server-provided JDBC connection pool data source which in turn needs the MySQL JDBC driver.

回答2:

Since you are running it in servlet, you need to have the jar accessible by the servlet container. You either include the connector as part of your application war or put it as part of the servlet container's extended library and datasource management stuff, if it has one. The second part is totally depend on the container that you have.

回答3:

The others are right about making the driver JAR available to your servlet container. My comment was meant to suggest that you verify from the command line whether the driver itself is intact.

Rather than an empty main(), try something like this, adapted from the included documentation:

public class LoadDriver {
    public static void main(String[] args) throws Exception {
        Class.forName("com.mysql.jdbc.Driver");
    }
}

On my platform, I'd do this:

$ ls mysql-connector-java-5.1.12-bin.jar 
mysql-connector-java-5.1.12-bin.jar
$ javac LoadDriver.java 
$ java -cp mysql-connector-java-5.1.12-bin.jar:. LoadDriver

On your platform, you need to use ; as the path separator, as discussed here and here.

回答4:

Place mysql-connector-java-5.1.6-bin.jar to the \Apache Tomcat 6.0.18\lib folder. Your problem will be solved.

回答5:

What you should not do do (especially when working on a shared project)

Ok, after had the same issue and after reading some answers here and other places. it seems that putting external lib into WEB-INF/lib is not that good idea as it pollute webapp/JRE libs with server-specific libraries - for more information check this answer"

Another solution that i do NOT recommend is: to copy it into tomcat/lib folder. although this may work, it will be hard to manage dependency for a shared(git for example) project.

Good solution 1

Create vendor folder. put there all your external lib. then, map this folder as dependency to your project. in eclipse you need to

add your folder to the build path
1. Project Properties -> Java build path
2. Libraries -> add external lib or any other solution to add your files/folder
add your build path to deployment Assembly (reference)
1. Project Properties -> Deployment Assembly
2. Add -> Java Build Path Entries
3. You should now see the list of libraries on your build path that you can specify for inclusion into your finished WAR.
4. Select the ones you want and hit Finish.

Good solution 2

Use maven (or any alternative) to manage project dependency

回答6:

Just follow these steps:

1) Install eclipse
2) Import Apache to eclipse
3) Install mysql
4) Download mysqlconnector/J
5) Unzip the zipped file navigate through it until you get the bin file in it. Then place all files that are present in the folder containing bin to C:\Program Files\mysql\mysql server5.1/ then give the same path as the address while defining the driver in eclipse.

That's all very easy guys.

回答7:

If the problem still persists,

Put the- mysql-connector-java-5.0.8-bin jar in a place inside your Tomcat->lib->folder (No matter where you've installed your Tomcat). And change your environmental variable (Done by clicking Properties of Mycomputer -Advanced system settings- Environmental variables-And set a new variable name & variable values as the place where your lib file resides.Dont forget to enter a ; at the end of the path)

If still problem persists Try downloading commons-collections-2.0.jar (http://www.docjar.com/jar_detail/commons-collections-2.0.jar.html) and paste the jar in the same place where your mysql jar resides (ie) inside Tomcat-lib.

Clean your project-Stop your server- Finally try to run.

回答8:

Many times I have been facing this problem, I have experienced ClassNotFoundException. if jar is not at physical location.

So make sure .jar file(mysql connector) in the physical location of WEB-INF lib folder. and make sure restarting Tomcat by using shutdown command in cmd. it should work.

回答9:

The only solution worked for me is putting the .jar file under WEB-INF/lib . Hope this will help.

回答10:

assuming your project is maven based, add it to your POM:

    <dependency>
        <groupId>mysql</groupId>
        <artifactId>mysql-connector-java</artifactId>
        <version>5.1.26</version>
    </dependency>

Save > Build > and test connection again. It works! Your actual mysql java connector version may vary.

回答11:

Put mysql-connector-java-5.1.38-bin.jar to the C:\Program Files\Apache Software Foundation\Tomcat 7.0\lib folder.by doing this program with execute

回答12:

My issue was a little different. Instead of jdbc:oracle:thin:@server:port/service i had it as server:port/service.

Missing was jdbc:oracle:thin:@ in url attribute in GlobalNamingResources.Resource. But I overlooked tomcat exception's

java.sql.SQLException: Cannot create JDBC driver of class 'oracle.jdbc.driver.OracleDriver' for connect URL 'server:port/service'

回答13:

for this error:

java.lang.ClassNotFoundException: com.mysql.jdbc.Driver

you need to:

Import java.sql.*;
Import com.mysql.jdbc.Driver;

even if its not used till app running.

来源：https://stackoverflow.com/questions/65166707/java-servlet-web-app-jdbc-oracle-connection

标签

eclipse

jakarta-ee

jdbc

classnotfoundexception