Unsupported major.minor version 52.0解决

最近开始玩hadoop，按照慕课网的教程，写好了WordCount类，代码如下：

package hadoop.study;

import java.io.IOException;
import java.util.StringTokenizer;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
import org.apache.hadoop.io.LongWritable;
import org.apache.hadoop.io.Text;
import org.apache.hadoop.mapreduce.Job;
import org.apache.hadoop.mapreduce.Mapper;
import org.apache.hadoop.mapreduce.Reducer;
import org.apache.hadoop.mapreduce.lib.input.FileInputFormat;
import org.apache.hadoop.mapreduce.lib.input.TextInputFormat;
import org.apache.hadoop.mapreduce.lib.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;

public class WordCount {
    public static class WordCountMap extends
            Mapper {
        private final IntWritable one = new IntWritable(1);
        private Text word = new Text();

        public void map(LongWritable key, Text value, Context context)
                throws IOException, InterruptedException {
            String line = value.toString();
            StringTokenizer token = new StringTokenizer(line);
            while (token.hasMoreTokens()) {
                word.set(token.nextToken());
                context.write(word, one);
            }
        }
    }

    public static class WordCountReduce extends
            Reducer {
        public void reduce(Text key, Iterable values,
                           Context context) throws IOException, InterruptedException {
            int sum = 0;
            for (IntWritable val : values) {
                sum += val.get();
            }
            context.write(key, new IntWritable(sum));
        }
    }

    public static void main(String[] args) throws Exception {
        Configuration conf = new Configuration();
        Job job = new Job(conf);
        job.setJarByClass(WordCount.class);
        job.setJobName("wordcount");
        job.setOutputKeyClass(Text.class);
        job.setOutputValueClass(IntWritable.class);
        job.setMapperClass(WordCountMap.class);
        job.setReducerClass(WordCountReduce.class);
        job.setInputFormatClass(TextInputFormat.class);
        job.setOutputFormatClass(TextOutputFormat.class);
        FileInputFormat.addInputPath(job, new Path(args[0]));
        FileOutputFormat.setOutputPath(job, new Path(args[1]));
        job.waitForCompletion(true);
    }
}

上传到Linux服务器上，该服务器上我已经搭建好了hadoop-1.2.1

上传上去后，执行如下命令编译：

javac -classpath /home/denglinjie/hadoop-1.2.1/hadoop-core-1.2.1.jar -d word_count_class/ WordCount.java

然后打成jar包：

jar -cvf wordcount.jar *.class

最后来启动主程序：

hadoop jar word_count_class/wordcount.jar WordCount input_wordcount output_wordcount

但是遗憾的是报了如下错误：

Unsupported major.minor version 52.0

错误原因是：

hadoop的版本和jdk的版本不对应，这里要用jdk1.6，所以编译的时候要加上如下参数

javac -source 1.6 -classpath /home/denglinjie/hadoop-1.2.1/hadoop-core-1.2.1.jar -d word_count_class/ WordCount.java