[英]Cannot run jar file because of “Could not find or load main class”
I have a test dir, which contains 3 folders: 我有一个测试目录,其中包含3个文件夹:
--META-INF:
one file MANIFEST.MF in the dir:
MANIFEST.MF:
anifest-Version: 1.0
Created-By: 1.7.0_04-ea (Oracle Corporation)
Class-Path: lib/*; .
Main-Class: Setup.WordCount
-- lib:
all the external jars I need for the project
-- Setup:
3 files in the dir:
WordCount$IntSumReducer.clas
WordCount$TokenizerMapper.class
WordCount.class
I create a jar file using the command 我使用以下命令创建一个jar文件
jar cmf test.jar test/META-INF/MANIFEST.MF test/Setup test/lib
but when I try to run the test.jar
, an error reported: 但是当我尝试运行test.jar
,报告了一个错误:
Error: Could not find or load main class Setup.WordCount
I've tried to debug the prob for the whole day, still no idea! 我已经整天尝试调试问题了,还是不知道!
WordCount.java
: WordCount.java
:
package Setup;
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.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.util.GenericOptionsParser;
public class WordCount {
public static class TokenizerMapper
extends Mapper<Object, Text, Text, IntWritable>{
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(Object key, Text value, Context context
) throws IOException, InterruptedException {
StringTokenizer itr = new StringTokenizer(value.toString());
while (itr.hasMoreTokens()) {
word.set(itr.nextToken());
context.write(word, one);
}
}
}
public static class IntSumReducer
extends Reducer<Text,IntWritable,Text,IntWritable> {
private IntWritable result = new IntWritable();
public void reduce(Text key, Iterable<IntWritable> values,
Context context
) throws IOException, InterruptedException {
int sum = 0;
for (IntWritable val : values) {
sum += val.get();
}
result.set(sum);
context.write(key, result);
}
}
public static void main(String[] args) throws Exception {
Configuration conf = new Configuration();
String[] otherArgs = new GenericOptionsParser(conf, args).getRemainingArgs();
if (otherArgs.length != 2) {
System.err.println("Usage: wordcount <in> <out>");
System.exit(2);
}
Job job = new Job(conf, "word count");
job.setJarByClass(WordCount.class);
job.setMapperClass(TokenizerMapper.class);
job.setCombinerClass(IntSumReducer.class);
job.setReducerClass(IntSumReducer.class);
job.setOutputKeyClass(Text.class);
job.setOutputValueClass(IntWritable.class);
FileInputFormat.addInputPath(job, new Path(otherArgs[0]));
FileOutputFormat.setOutputPath(job, new Path(otherArgs[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
The code is exactly the same as hadoop/example/WordCount
, I'm trying to implementing hadoop example on my local dev environment. 代码与hadoop/example/WordCount
完全相同,我试图在本地开发环境中实现hadoop示例。
Your jar statement is slightly off. 您的jar语句略有偏离。 Try this: 尝试这个:
jar -cfm test.jar test/META-INF/MANIFEST.MF -C test Setup -C test lib
Your command puts test/Setup/WordCount.class in the jar, which is why Java cannot find Setup/WordCount.class 您的命令将test / Setup / WordCount.class放入jar中,这就是Java无法找到Setup / WordCount.class的原因
You are also missing the package statement in the code you posted: 您还缺少发布的代码中的package语句:
package Setup;
specify package in code - and than use it in start command/ eg: 在代码中指定包-然后在启动命令/中使用它,例如:
hadoop jar mywordcount.jar hadoop.mytest.WordCount input22/input /home/training/output
where hadoop.mytest.WordCount
- is your package 在哪里hadoop.mytest.WordCount
是您的软件包
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