今天小编给大家分享一下怎么利用Java连接Hadoop进行编程的相关知识点，内容详细，逻辑清晰，相信大部分人都还太了解这方面的知识，所以分享这篇文章给大家参考一下，希望大家阅读完这篇文章后有所收获，下面我们一起来了解一下吧。
实验环境
hadoop版本：3.3.2
jdk版本：1.8
hadoop安装系统：ubuntu18.04
编程环境：IDEA
编程主机：windows
实验内容
测试Java远程连接hadoop
创建maven工程，引入以下依赖：
<dependency> <groupId>org.testng</groupId> <artifactId>testng</artifactId> <version>RELEASE</version> <scope>compile</scope> </dependency> <dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-common</artifactId> </dependency> <dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-hdfs</artifactId> <version>3.3.2</version> </dependency> <dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-common</artifactId> <version>3.3.2</version> </dependency> <dependency> <groupId>org.apache.hadoop</groupId> <artifactId>hadoop-core</artifactId> <version>1.2.1</version> </dependency>虚拟机的/etc/hosts配置
hdfs-site.xml配置
<configuration> <property> <name>dfs.replication</name> <value>1</value> </property> <property> <name>dfs.namenode.name.dir</name> <value>file:/root/rDesk/hadoop-3.3.2/tmp/dfs/name</value> </property> <property> <name>dfs.datanode.http.address</name> <value>VM-12-11-ubuntu:50010</value> </property> <property> <name>dfs.client.use.datanode.hostname</name> <value>true</value> </property> <property> <name>dfs.datanode.data.dir</name> <value>file:/root/rDesk/hadoop-3.3.2/tmp/dfs/data</value> </property></configuration>
core-site.xml配置
<configuration> <property> <name>hadoop.tmp.dir</name> <value>file:/root/rDesk/hadoop-3.3.2/tmp</value> <description>Abase for other temporary directories.</description> </property> <property> <name>fs.defaultFS</name> <value>hdfs://VM-12-11-ubuntu:9000</value> </property></configuration>
启动hadoop
sbin/start-dfs.sh
主机的hosts（C:\Windows\System32\drivers\etc）文件配置
尝试连接到虚拟机的hadoop并读取文件内容，这里我读取hdfs下的/root/iinput文件内容
Java代码：
import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FileStatus;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.hdfs.DistributedFileSystem;public class TestConnectHadoop { public static void main(String[] args) throws Exception { String hostname = "VM-12-11-ubuntu"; String HDFS_PATH = "hdfs://" + hostname + ":9000"; Configuration conf = new Configuration(); conf.set("fs.defaultFS", HDFS_PATH); conf.set("fs.hdfs.impl", DistributedFileSystem.class.getName()); conf.set("dfs.client.use.datanode.hostname", "true"); FileSystem fs = FileSystem.get(conf); FileStatus[] fileStatuses = fs.listStatus(new Path("/")); for (FileStatus fileStatus : fileStatuses) { System.out.println(fileStatus.toString()); } FileStatus fileStatus = fs.getFileStatus(new Path("/root/iinput")); System.out.println(fileStatus.getOwner()); System.out.println(fileStatus.getGroup()); System.out.println(fileStatus.getPath()); FSDataInputStream open = fs.open(fileStatus.getPath()); byte[] buf = new byte[1024]; int n = -1; StringBuilder sb = new StringBuilder(); while ((n = open.read(buf)) > 0) { sb.append(new String(buf, 0, n)); } System.out.println(sb); }}运行结果：
编程实现一个类“MyFSDataInputStream”，该类继承“org.apache.hadoop.fs.FSDataInputStream",要求如下： ①实现按行读取HDFS中指定文件的方法”readLine（）“，如果读到文件末尾，则返回为空，否则返回文件一行的文本
思路：emmm我的思路比较简单，只适用于该要求，仅作参考。
将所有的数据读取出来存储起来，然后根据换行符进行拆分，将拆分的字符串数组存储起来，用于readline返回
Java代码
import org.apache.hadoop.fs.FSDataInputStream;import java.io.IOException;import java.io.InputStream;public class MyFSDataInputStream extends FSDataInputStream { private String data = null; private String[] lines = null; private int count = 0; private FSDataInputStream in; public MyFSDataInputStream(InputStream in) throws IOException { super(in); this.in = (FSDataInputStream) in; init(); } private void init() throws IOException { byte[] buf = new byte[1024]; int n = -1; StringBuilder sb = new StringBuilder(); while ((n = this.in.read(buf)) > 0) { sb.append(new String(buf, 0, n)); } data = sb.toString(); lines = data.split("\n"); } public String read_line() { return count < lines.length ? lines[count++] : null; }}测试类：
import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FileStatus;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;import org.apache.hadoop.hdfs.DistributedFileSystem;public class TestConnectHadoop { public static void main(String[] args) throws Exception { String hostname = "VM-12-11-ubuntu"; String HDFS_PATH = "hdfs://" + hostname + ":9000"; Configuration conf = new Configuration(); conf.set("fs.defaultFS", HDFS_PATH); conf.set("fs.hdfs.impl", DistributedFileSystem.class.getName()); conf.set("dfs.client.use.datanode.hostname", "true"); FileSystem fs = FileSystem.get(conf); FileStatus fileStatus = fs.getFileStatus(new Path("/root/iinput")); System.out.println(fileStatus.getOwner()); System.out.println(fileStatus.getGroup()); System.out.println(fileStatus.getPath()); FSDataInputStream open = fs.open(fileStatus.getPath()); MyFSDataInputStream myFSDataInputStream = new MyFSDataInputStream(open); String line = null; int count = 0; while ((line = myFSDataInputStream.read_line()) != null ) { System.out.printf("line %d is: %s\n", count++, line); } System.out.println("end"); }}运行结果：
②实现缓存功能，即利用”MyFSDataInputStream“读取若干字节数据时，首先查找缓存，如果缓存中有所需要数据，则直接由缓存提供，否则从HDFS中读取数据
import org.apache.hadoop.fs.FSDataInputStream;import java.io.BufferedInputStream;import java.io.IOException;import java.io.InputStream;public class MyFSDataInputStream extends FSDataInputStream { private BufferedInputStream buffer; private String[] lines = null; private int count = 0; private FSDataInputStream in; public MyFSDataInputStream(InputStream in) throws IOException { super(in); this.in = (FSDataInputStream) in; init(); } private void init() throws IOException { byte[] buf = new byte[1024]; int n = -1; StringBuilder sb = new StringBuilder(); while ((n = this.in.read(buf)) > 0) { sb.append(new String(buf, 0, n)); } //缓存数据读取 buffer = new BufferedInputStream(this.in); lines = sb.toString().split("\n"); } public String read_line() { return count < lines.length ? lines[count++] : null; } @Override public int read() throws IOException { return this.buffer.read(); } public int readWithBuf(byte[] buf, int offset, int len) throws IOException { return this.buffer.read(buf, offset, len); } public int readWithBuf(byte[] buf) throws IOException { return this.buffer.read(buf); }}以上就是“怎么利用Java连接Hadoop进行编程”这篇文章的所有内容，感谢各位的阅读！相信大家阅读完这篇文章都有很大的收获，小编每天都会为大家更新不同的知识，如果还想学习更多的知识，请关注编程网行业资讯频道。
