MySql driver not found for Scala program

问题:

I'm a newbie on Scala, am trying to use Spark to read from a mysql database. I'm facing a class-not-found exception whatever I do. I tried to connect without Spark, using Squeryl, Scalike, etc. Always the same problem. Here's one example I tried :

logger.info("Write part")

val dataframe_mysql = spark.sqlContext
  .read.format("jdbc")
  .option("url", s"jdbc:mysql://${datamart_server}:3306/vol")
  .option("driver", "com.mysql.jdbc.Driver")
  .option("dbtable", "company")
  .option("user", datamart_user).option("password", datamart_pwd)
  .load()

dataframe_mysql.show()

I tried to put the driver classname in a src/main/resources/application.conf:

db.default.driver="com.mysql.jdbc.Driver"

But it didn't help. I've got :

java.sql.SQLException: No suitable driver

I also share the sbt file to show how I add the dependencies :

name := "commercial-api-datamart-feed"
version := "0.1"
scalaVersion := "2.11.6"
libraryDependencies += "org.scala-lang.modules" %% "scala-parser-combinators" % "1.1.0"
libraryDependencies += "ch.qos.logback" % "logback-classic" % "1.1.3" % Runtime
libraryDependencies += "com.typesafe.scala-logging" %% "scala-logging" % "3.9.0"
libraryDependencies += "org.apache.spark" %% "spark-core" % "2.3.0"
libraryDependencies += "org.apache.spark" %% "spark-sql" % "2.3.0"
libraryDependencies += "mysql" % "mysql-connector-java" % "5.1.24" % Runtime

Spark is not mandatory but I think it's better for performance.

回答1:

How are you running this code? You'll need to pass the MySQL JAR as --jars; something like --jars /path/to/mysql.jar if starting up spark-shell or spark-submit.

If you prefer running a single JAR, you'll need to ensure that the MySQL JAR is embedded as part of your uber JAR. I've never used SBT but you'll need to check whether the final JAR created has the MySQL classes inside it -- if not, use the relevant SBT flags to make that happen.

回答2:

You have to make sure the mysql dependencies exist on all of the executors. In my environment, I use maven and specify the dependency like this inside of my pom.xml:

<dependency>
  <groupId>mysql</groupId>
  <artifactId>mysql-connector-java</artifactId>
  <version>5.1.42</version>
</dependency>

I then ensure that this dependency is bundled in my application jar (using the maven shade plugin), so that I don't have to place the jar on all of the executors.

Whether you use spark or not to access mysql over jdbc, you need to make sure the mysql-connector is available on your classpath, wherever you are executing mysql queries from.