IncompatibleClassChangeError when running spark from (spring) servlet

When running a simple spark job from a (spring) web app, I get an IncompatibleClassChangeError. It is probably due to some incompatible dependencies, but I cannot find which.

To put it simply, this is the issue with exception stack.

Here is the failing code:

// file conversion with spark
// --------------------------
JavaRDD<String> inputRdd = sparkContext.textFile(inputFile).cache();

Function fct = new Function<String,String>() {
    @Override
    public String call(String line) throws Exception {
        return line.toUpperCase();
    }
};
JavaRDD<Strineg> outputRdd = inputRdd.map(fct); // *** fail ***

outputRdd.saveAsTextFile(outputDir);

And it is called from a simple spring servlet:

@RequestMapping(method = RequestMethod.GET, value="/upper")
public @ResponseBody boolean upper(@RequestParam(required = true) String inputFile,
                                   @RequestParam(required = true) String outputDir,
                                   @RequestParam(required = false) String master,
                                   @RequestParam(required = false) String namenode) {
    if(master==null) master = "local";
    SparkUpper.upper(inputFile, outputDir, master, namenode);

    return true;
}

And here is the (maven) dependencies:

<dependencies>
  <!-- spring -->
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-context</artifactId>
    <version>${spring.version}</version>
  </dependency>
  <dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-webmvc</artifactId>
    <version>${spring.version}</version>
  </dependency>

  <!-- spark & hadoop -->
  <dependency>
    <groupId>org.apache.spark</groupId>
    <artifactId>spark-core_2.10</artifactId>
    <version>1.2.1</version>
  </dependency>
  <dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-core</artifactId>
    <version>1.2.1</version>
  </dependency>
  <dependency>
    <groupId>org.apache.hadoop</groupId>
    <artifactId>hadoop-client</artifactId>
    <version>2.5.2</version>
  </dependency>

</dependencies>

The strange thing is that is basically do the same, with same spark dependencies but called from a servlet, as in this project that works fine.

Any idea would be greatly appreciated.