Hadoop的Mapper和Reducer如何共享变量

代码

public class ShortestPath {
static Map<String, Integer> map=new HashMap<String, Integer>();

public static class TokenizerMapper extends Mapper<LongWritable, Text, Text, Text> {
public void map(LongWritable key, Text value, Context context)
throws IOException, InterruptedException {
map.put("test",123");
}
}

public static class ShortestPathReducer extends Reducer<Text, Text, Text, Text> {
public void reduce(Text key, Iterable<Text> values, Context context)
throws IOException, InterruptedException {
map.put("test",123");
}
}

public static void main(String[] args) throws Exception {
　　System.out.println(map.toString());
}
}

虽然编译成功，但在main中的输出显示，map为null。

求教如何使mapper和reducer能共享变量？