借助Maven搭建Hadoop开发环境的最详细教程分享
介绍
在开发Hadoop应用程序时,使用Maven来管理依赖项和构建过程是很方便的。本文将介绍如何在MacOS上使用Maven搭建Hadoop开发环境。
前置条件
- 安装Java
- 安装Maven
- 下载安装文件:hadoop-x.x.x.tar.gz
步骤
步骤一:解压hadoop安装文件
在命令行中进入到下载好的hadoop-x.x.x.tar.gz所在的目录下,输入以下命令进行解压:
tar -xzvf hadoop-x.x.x.tar.gz
解压完成后,进入到hadoop-x.x.x目录中。
步骤二:配置环境变量
编辑.bashrc文件,在文件末尾加入以下内容:
export HADOOP_HOME=/path/to/hadoop-x.x.x
export PATH=$PATH:$HADOOP_HOME/bin
export HADOOP_CONF_DIR=$HADOOP_HOME/etc/hadoop
其中,/path/to/hadoop-x.x.x是指hadoop-x.x.x所在的目录路径。
为了使修改立即生效,可以输入以下命令:
source ~/.bashrc
步骤三:设置Maven依赖项
在Maven工程中,需要使用hadoop-common、hadoop-hdfs、hadoop-mapreduce-client-core等jar包。需要在pom.xml文件中加入以下依赖项:
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>2.7.3</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>2.7.3</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-mapreduce-client-core</artifactId>
<version>2.7.3</version>
</dependency>
步骤四:使用Maven构建Hadoop项目
在Maven工程的根目录下运行以下命令来构建项目:
mvn clean package
例一:WordCount示例
创建一个WordCount类,用于统计文件中的单词数量。
import java.nio.file.FileSystem;
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.LongWritable;
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;
public class WordCount {
public static class TokenizerMapper extends Mapper<LongWritable, Text, Text, IntWritable> {
private final static IntWritable one = new IntWritable(1);
private Text word = new Text();
public void map(LongWritable 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();
Job job = Job.getInstance(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(args[0]));
FileOutputFormat.setOutputPath(job, new Path(args[1]));
System.exit(job.waitForCompletion(true) ? 0 : 1);
}
}
例二:HDFS示例
在HDFS上读取和写入文件,创建一个HdfsClient类。
import java.io.InputStream;
import java.net.URI;
import java.nio.file.FileSystem;
import java.nio.file.FileSystems;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
public class HdfsClient {
private static Configuration conf = new Configuration();
private static String uri = "hdfs://localhost:9000";
private static org.apache.hadoop.fs.FileSystem hdfs;
public static void main(String[] args) throws Exception {
hdfs = FileSystem.get(new URI(uri), conf);
// 读取文件
Path readPath = new Path("/test/file");
InputStream in = hdfs.open(readPath);
byte[] data = new byte[1024];
int length;
while ((length = in.read(data)) > 0) {
System.out.println(new String(data, 0, length));
}
// 写入文件
String content = "Hello, Hadoop!";
Path writePath = new Path("/test/result.txt");
FSDataOutputStream os = hdfs.create(writePath);
os.write(content.getBytes("UTF-8"));
os.close();
hdfs.close();
}
}
结论
本文介绍了如何使用Maven搭建Hadoop开发环境,并给出了两个示例:WordCount和HDFS。使用Maven管理依赖项和构建过程,可以极大地简化Hadoop开发流程,提高开发效率。
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