Unsupported major.minor version 52.0解决

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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<LongWritable, Text, Text, IntWritable> {        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<Text, IntWritable, Text, IntWritable> {        public void reduce(Text key, Iterable<IntWritable> 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

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