java mongo MapReduce

//Map过程，通过emit函数实现，第一个参数表示用于分组的字段，    //第二个参数表示分组字段所对应的值    String map="function() {" +       "emit(this.期刊," +        "{count: 1, ref: this.参考文献}); " +       "}";    //Reduce过程，遍历values，填充相应业务逻辑。    String reduce="function(key, values) {" +    "var reduced = {articlecount:0, refcount:0};" +    "values.forEach(function(val) {" +    "for(var r in val.ref)" +    "reduced.refcount  += 1;" +    "reduced.articlecount += 1; });" +    "return reduced;}";    //Finalize过程，针对MapRecuce结果，填充相应业务逻辑。    String finalize = "function(key, reduced) " +    "{reduced.avgRefcount = reduced.refcount / reduced.articlecount;" +    "return reduced;}";    MapReduceCommand cmd = new MapReduceCommand(table , map, reduce,      null, MapReduceCommand.OutputType.INLINE, null);    cmd.setFinalize(finalize);    MapReduceOutput out = table.mapReduce(cmd);