解决Eclipse中运行WordCount出现 java.lang.ClassNotFoundException: org.apache.hadoop.exam

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import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.net.URL;
import java.net.URLClassLoader;
import java.util.ArrayList;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.jar.JarOutputStream;
import java.util.jar.Manifest;

public class EJob {

	// To declare global field
	private static List<URL> classPath = new ArrayList<URL>();

	// To declare method
	public static File createTempJar(String root) throws IOException {
		if (!new File(root).exists()) {
			return null;
		}
		Manifest manifest = new Manifest();
		manifest.getMainAttributes().putValue("Manifest-Version", "1.0");
		final File jarFile = File.createTempFile("EJob-", ".jar", new File(System.getProperty("java.io.tmpdir")));

		Runtime.getRuntime().addShutdownHook(new Thread() {
			public void run() {
				jarFile.delete();
			}
		});

		JarOutputStream out = new JarOutputStream(new FileOutputStream(jarFile), manifest);
		createTempJarInner(out, new File(root), "");
		out.flush();
		out.close();
		return jarFile;
	}

	private static void createTempJarInner(JarOutputStream out, File f,
			String base) throws IOException {
		if (f.isDirectory()) {
			File[] fl = f.listFiles();
			if (base.length() > 0) {
				base = base + "/";
			}
			for (int i = 0; i < fl.length; i++) {
				createTempJarInner(out, fl[i], base + fl[i].getName());
			}
		} else {
			out.putNextEntry(new JarEntry(base));
			FileInputStream in = new FileInputStream(f);
			byte[] buffer = new byte[1024];
			int n = in.read(buffer);
			while (n != -1) {
				out.write(buffer, 0, n);
				n = in.read(buffer);
			}
			in.close();
		}
	}

	public static ClassLoader getClassLoader() {
		ClassLoader parent = Thread.currentThread().getContextClassLoader();
		if (parent == null) {
			parent = EJob.class.getClassLoader();
		}
		if (parent == null) {
			parent = ClassLoader.getSystemClassLoader();
		}
		return new URLClassLoader(classPath.toArray(new URL[0]), parent);
	}

	public static void addClasspath(String component) {
		if ((component != null) && (component.length() > 0)) {
			try {
				File f = new File(component);
				if (f.exists()) {
					URL key = f.getCanonicalFile().toURI().toURL();
					if (!classPath.contains(key)) {
						classPath.add(key);
					}
				}
			} catch (IOException e) {
			}
		}
	}

}

// mian方法中添加:

File jarFile = EJob.createTempJar("bin");
EJob.addClasspath("/usr/hadoop/conf");
ClassLoader classLoader = EJob.getClassLoader();
Thread.currentThread().setContextClassLoader(classLoader);

job.waitForCompletion(true) 提交之前加上下面一条:

((JobConf) job.getConfiguration()).setJar(jarFile.toString());

demo如下:

package mr2demo;

import java.io.File;
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.mapred.JobConf;
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 void main(String[] args) throws Exception {

		File jarFile = EJob.createTempJar("bin");
		EJob.addClasspath("E:\\workspace\\hadoop\\mapreduce\\mr2demo\\conf");
		ClassLoader classLoader = EJob.getClassLoader();
		Thread.currentThread().setContextClassLoader(classLoader);

		Configuration conf = new Configuration();
		String[] otherArgs = new GenericOptionsParser(conf, args)
				.getRemainingArgs();
		if (otherArgs.length < 2) {
			System.err.println("Usage: wordcount <in> [<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);
		for (int i = 0; i < otherArgs.length - 1; i++) {
			FileInputFormat.addInputPath(job, new Path(otherArgs[i]));
		}
		FileOutputFormat.setOutputPath(job, new Path(otherArgs[(otherArgs.length - 1)]));

		((JobConf) job.getConfiguration()).setJar(jarFile.toString());

		System.exit(job.waitForCompletion(true) ? 0 : 1);
	}

	public static class IntSumReducer extends Reducer<Text, IntWritable, Text, IntWritable> {
		private IntWritable result = new IntWritable();

		public void reduce(Text key, Iterable<IntWritable> values, Reducer<Text, IntWritable, Text, IntWritable>.Context context) throws IOException, InterruptedException {
			int sum = 0;
			for (IntWritable val : values) {
				sum += val.get();
			}
			this.result.set(sum);
			context.write(key, this.result);
		}
	}

	public static class TokenizerMapper extends Mapper<Object, Text, Text, IntWritable> {
		private static final IntWritable one = new IntWritable(1);
		private Text word = new Text();

		public void map(Object key, Text value, Mapper<Object, Text, Text, IntWritable>.Context context) throws IOException, InterruptedException {
			StringTokenizer itr = new StringTokenizer(value.toString());
			while (itr.hasMoreTokens()) {
				this.word.set(itr.nextToken());
				context.write(this.word, one);
			}
		}
	}
}

以上解决了eclipse和插件因为兼容性，导致无法生成jar，windows上无法运行job。