再來看一個分數統計的小例子。

        在Hive中存在如下一張表：

1. hive> describe tb_test2;  
2. OK  
3. name    string    
4. score_list  array<map<string,int>>    
5. Time taken: 0.074 seconds  
6. hive> select * from tb_test2;  
7. OK  
8. A   [{"math":100,"english":90,"history":85}]  
9. B   [{"math":95,"english":80,"history":100}]  
10. C   [{"math":80,"english":90,"histroy":100}]  
11. Time taken: 0.107 seconds  

        編寫genericUDF.

1. package com.wz.udf;  
2. import org.apache.hadoop.io.Text;  
3. import org.apache.hadoop.io.IntWritable;  
4. import org.apache.hadoop.hive.ql.udf.generic.GenericUDF;  
5. import org.apache.hadoop.hive.ql.exec.UDFArgumentException;  
6. import org.apache.hadoop.hive.ql.exec.UDFArgumentLengthException;  
7. import org.apache.hadoop.hive.ql.exec.UDFArgumentTypeException;  
8. import org.apache.hadoop.hive.ql.metadata.HiveException;  
9. import org.apache.hadoop.hive.serde2.lazy.LazyString;  
10. import org.apache.hadoop.hive.serde2.lazy.LazyMap;  
11. import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector;  
12. import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspector.Category;  
13. import org.apache.hadoop.hive.serde2.objectinspector.ListObjectInspector;  
14. import org.apache.hadoop.hive.serde2.objectinspector.MapObjectInspector;  
15. import org.apache.hadoop.hive.serde2.objectinspector.StructObjectInspector;  
16. import org.apache.hadoop.hive.serde2.objectinspector.StandardListObjectInspector;  
17. import org.apache.hadoop.hive.serde2.objectinspector.ObjectInspectorFactory;  
18. import org.apache.hadoop.hive.serde2.objectinspector.StructField;  
19. import org.apache.hadoop.hive.serde2.objectinspector.PrimitiveObjectInspector;  
20. import org.apache.hadoop.hive.serde2.objectinspector.primitive.PrimitiveObjectInspectorFactory;  
21. import org.apache.hadoop.hive.serde2.objectinspector.primitive.StringObjectInspector;  
22. import java.util.ArrayList;  
23. publicclass helloGenericUDFNew extends GenericUDF {  
24.      ////輸入變數定義
25.      private ObjectInspector nameObj;  
26.      private ListObjectInspector listoi;  
27.      private MapObjectInspector mapOI;  
28.      private ArrayList<Object> valueList = new ArrayList<Object>();   
29.      @Override
30.      public ObjectInspector initialize(ObjectInspector[] arguments) throws UDFArgumentException {  
31.           nameObj = (ObjectInspector)arguments[0];  
32.           listoi = (ListObjectInspector)arguments[1];  
33.       mapOI = ((MapObjectInspector)listoi.getListElementObjectInspector());  
34.           //輸出結構體定義
35.           ArrayList structFieldNames = new ArrayList();  
36.           ArrayList structFieldObjectInspectors = new ArrayList();  
37.           structFieldNames.add("name");  
38.       structFieldNames.add("totalScore");  
39.           structFieldObjectInspectors.add( PrimitiveObjectInspectorFactory.writableStringObjectInspector );  
40.           structFieldObjectInspectors.add( PrimitiveObjectInspectorFactory.writableIntObjectInspector );  
41.           StructObjectInspector si2;  
42.           si2 = ObjectInspectorFactory.getStandardStructObjectInspector(structFieldNames, structFieldObjectInspectors);   
43.           return si2;  
44.      }  
45.      @Override
46.      public Object evaluate(DeferredObject[] arguments) throws HiveException{  
47.       LazyString LName = (LazyString)(arguments[0].get());  
48.       String strName = ((StringObjectInspector)nameObj).getPrimitiveJavaObject( LName );  
49.       int nelements = listoi.getListLength(arguments[1].get());  
50.           int nTotalScore=0;  
51.           valueList.clear();  
52.           //遍歷list
53.       for(int i=0;i<nelements;i++)  
54.       {   
55.                LazyMap LMap = (LazyMap)listoi.getListElement(arguments[1].get(),i);  
56.                //獲取map中的所有value值
57.            valueList.addAll(mapOI.getMap(LMap).values());   
58.                for (int j = 0; j < valueList.size(); j++)  
59.            {  
60.                    nTotalScore+=Integer.parseInt(valueList.get(j).toString());  
61.                }                 
62.           }  
63.       Object[] e;     
64.       e = new Object[2];  
65.       e[0] = new Text(strName);  
66.           e[1] = new IntWritable(nTotalScore);  
67.           return e;  
68.      }  
69.      @Override
70.      public String getDisplayString(String[] children) {  
71.           assert( children.length>0 );  
72.           StringBuilder sb = new StringBuilder();  
73.           sb.append("helloGenericUDFNew(");  
74.           sb.append(children[0]);  
75.           sb.append(")");  
76.           return sb.toString();  
77.      }  
78. }  

        在Hive中執行，結果如下:

1. hive> add jar /home/wangzhun/hive/hive-0.8.1/lib/helloGenericUDFNew.jar;      
2. Added /home/wangzhun/hive/hive-0.8.1/lib/helloGenericUDFNew.jar to class path  
3. Added resource: /home/wangzhun/hive/hive-0.8.1/lib/helloGenericUDFNew.jar  
4. hive> create temporary function hellonew as 'com.wz.udf.helloGenericUDFNew';  
5. OK  
6. Time taken: 0.016 seconds  
7. hive> select hellonew(tb_test2.name,tb_test2.score_list) from tb_test2;       
8. Total MapReduce jobs = 1  
9. Launching Job 1 out of 1  
10. Number of reduce tasks is set to 0 since there's no reduce operator  
11. Starting Job = job_201312091733_0018, Tracking URL = http://localhost:50030/jobdetails.jsp?jobid=job_201312091733_0018  
12. Kill Command = /home/wangzhun/hadoop/hadoop-0.20.2/bin/../bin/hadoop job  -Dmapred.job.tracker=localhost:9001 -kill job_201312091733_0018  
13. Hadoop job information for Stage-1: number of mappers: 1; number of reducers: 0  
14. 2013-12-09 22:31:22,328 Stage-1 map = 0%,  reduce = 0%  
15. 2013-12-09 22:31:25,354 Stage-1 map = 100%,  reduce = 0%  
16. 2013-12-09 22:31:28,390 Stage-1 map = 100%,  reduce = 100%  
17. Ended Job = job_201312091733_0018  
18. MapReduce Jobs Launched:   
19. Job 0: Map: 1   HDFS Read: 99 HDFS Write: 18 SUCESS  
20. Total MapReduce CPU Time Spent: 0 msec  
21. OK  
22. {"people":"A","totalscore":275}  
23. {"people":"B","totalscore":275}  
24. {"people":"C","totalscore":270}  
25. Time taken: 21.7 seconds