Java Hadoop Mapreduce:未调用Reduce方法
我正在写一个mapreduce算法 在我的代码中,不调用Java Hadoop Mapreduce:未调用Reduce方法,java,hadoop,mapreduce,reduce,Java,Hadoop,Mapreduce,Reduce,我正在写一个mapreduce算法 在我的代码中,不调用reduce(文本键、Iterable值、上下文)方法。在它上面我有一个@Override给出了一个错误:方法没有从它的超类中重写方法 这是我的密码: package WordCountP; import java.io.FileReader; import java.io.IOException; import java.util.Iterator; import org.apache.hadoop.conf.Configured;
reduce(文本键、Iterable值、上下文)
方法。在它上面我有一个@Override
给出了一个错误:方法没有从它的超类中重写方法
这是我的密码:
package WordCountP;
import java.io.FileReader;
import java.io.IOException;
import java.util.Iterator;
import org.apache.hadoop.conf.Configured;
import org.apache.hadoop.fs.Path;
import org.apache.hadoop.io.IntWritable;
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.output.FileOutputFormat;
import org.apache.hadoop.mapreduce.lib.output.TextOutputFormat;
import org.apache.hadoop.util.Tool;
import org.apache.hadoop.util.ToolRunner;
import org.json.simple.JSONArray;
import org.json.simple.JSONObject;
import org.json.simple.parser.JSONParser;
import org.json.simple.parser.ParseException;
public class popularity extends Configured implements Tool{
public class PopularityMapper extends Mapper<Text, Text, Text, Text> {
@Override
protected void map(Text key, Text value,
Context context)
throws IOException, InterruptedException {
JSONParser jsonParser = new JSONParser();
try {
JSONObject jsonobject = (JSONObject) jsonParser.parse(new FileReader("src\\testinput.json"));
JSONArray jsonArray = (JSONArray) jsonobject.get("votes");
Iterator<JSONObject> iterator = jsonArray.iterator();
while(iterator.hasNext()) {
JSONObject obj = iterator.next();
String song_id_rave_id = (String) obj.get("song_ID") + "|" + (String) obj.get("rave_ID");
String preference = (String) obj.get("preference");
System.out.println(song_id_rave_id + "||" + preference);
context.write(new Text(song_id_rave_id), new Text(preference));
}
}catch(ParseException e) {
e.printStackTrace();
}
}
}
public class PopularityReducer extends Reducer<Text, Iterable<String>, Text, Text> {
@Override
protected void reduce(Text key, Iterable<String> values, Context context)
throws IOException, InterruptedException {
int sum = 0;
for ( String val: values){
if (val == "true"){
sum +=1;
}
else if (val == "false"){
sum -=1;
}
}
String result = Integer.toString(sum);
context.write(new Text(key), new Text(result));
}
}
public static void main(String[] args) throws Exception{
int exitCode = ToolRunner.run(new popularity(), args);
System.exit(exitCode);
}
public int run(String[] args) throws Exception {
if (args.length != 2) {
System.err.printf("Usage: %s [generic options] <input> <output>\n",
getClass().getSimpleName());
ToolRunner.printGenericCommandUsage(System.err);
return -1;
}
Job job = new org.apache.hadoop.mapreduce.Job();
job.setJarByClass(popularity.class);
job.setJobName("PopularityCounter");
FileInputFormat.addInputPath(job, new Path(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
job.setOutputFormatClass(TextOutputFormat.class);
job.setMapperClass(PopularityMapper.class);
job.setReducerClass(PopularityReducer.class);
int returnValue = job.waitForCompletion(true) ? 0:1;
System.out.println("job.isSuccessful " + job.isSuccessful());
return returnValue;
}
}
提前谢谢 同时检查IOException和InterruptedException,因此不会重写reduce方法
类Reducer中的方法reduce不会引发任何异常,因此您不能声明子类中的方法reduce会引发任何选中的异常,但它可以引发未选中的异常
您可能希望在reduce方法中处理异常。最后,我们选择了MongoBD-mapreduce
Hadoop太难了
谢谢 我试图在reduce方法中调整异常的位置,但这并没有解决问题。为什么这是一个问题?因为map()方法也会在override方法中抛出异常@TNelen是的,所以你也需要在map方法中做同样的更改,我相信当创建对象时,会使用父类引用,因此它会在父类中调用reduce和map方法,而不是你创建的方法。代码没有编译,也不是说没有调用该方法。。。一旦它运行,映射器是否工作正常?您没有覆盖默认的inputformat,因此地图类型不正确。我将reduce方法输入格式更改为,错误消失。不确定代码是否正常工作,我现在要测试。String不是writeable的子类,因此也不应该工作。默认映射器输入必须是LongWritable,Text
我知道了!这确实是我的映射器输入中的一个错误
{"votes":[{
"song_ID": "Piece of your heart",
"mbr_ID": "001",
"preference": "true",
"timestamp": "11:22:33",
"rave_ID": "rave001",
},
{
"song_ID": "Piece of your heart",
"mbr_ID": "002",
"preference": "true",
"timestamp": "11:22:33",
"rave_ID": "rave001",
},
{
"song_ID": "Atje voor de sfeer",
"mbr_ID": "001",
"preference": "false",
"timestamp": "11:44:33",
"rave_ID": "rave001",
},
{
"song_ID": "Atje voor de sfeer",
"mbr_ID": "002",
"preference": "false",
"timestamp": "11:44:33",
"rave_ID": "rave001",
},
{
"song_ID": "Atje voor de sfeer",
"mbr_ID": "003",
"preference": "true",
"timestamp": "11:44:33",
"rave_ID": "rave001",
}]
}