NameError：无法加载Java类com.mysql.jdbc.Driver

Question

I'm using JRuby 1.7.2, along with DataMapper, and I'm getting an error I can't find an answer to.

I'm just testing out DataMapper along with MySQL 5.5 to see if it will run fine when I build around it. Here's the file I'm testing:

require "data_mapper"
require "keys"

DataMapper.setup(:default, "mysql://#{$user}:#{$pass}@localhost/test_db")

And when I run this, I get the error:

NameError: cannot load Java class com.mysql.jdbc.Driver

And it points to the DataMapper.setup line.

My Gemfile should be alright:

source :rubygems

gem "sinatra"
gem "trinidad"
gem "data_mapper"

# do a `sudo apt-get install libmysqlclient-dev` first
gem "dm-mysql-adapter"
gem "jdbc-mysql"

Is there anything I'm missing? I have MySQL set up with a user/pass locally already.

Answer 1

This is a common error when running JDBC clients for MySQL . You need to make sure you have mysql-connector-java-bin.jar on the classpath. You can download it from here .

Answer 2

I'm using Rails 3.2.9 and to solve the problem I added this to my application.rb

if defined? JRUBY_VERSION
    require 'jdbc/mysql'
    Jdbc::MySQL.load_driver
end

Answer 3

actually, the correct answer is to work-around an incompatibility between 5.1.13 and 5.1.22 !

jdbc-mysql gem already contains the mysql-connector.jar it just ain't auto-loading anymore :

https://github.com/jruby/activerecord-jdbc-adapter/tree/master/jdbc-mysql (read the README)

you can also force the driver to auto-load using a Java system property eg from a cmd line :

jruby -J-Darjdbc.mysql.autoload=true -S rake ...

Answer 4

I had the same error when trying to use a mysql database from jruby/rails4. In my case this line was missing from ./Gemfile:

gem 'jdbc-mysql'