HDFS的Java访问接口
1）org.apache.hadoop.fs.FileSystem
是一个通用的文件系统API，提供了不同文件系统的统一访问方式。
2）org.apache.hadoop.fs.Path
是Hadoop文件系统中统一的文件或目录描述，类似于java.io.File对本地文件系统的文件或目录描述。
3）org.apache.hadoop.conf.Configuration
读取、解析配置文件(如core-site.xml/hdfs-default.xml/hdfs-site.xml等)，或添加配置的工具类
4）org.apache.hadoop.fs.FSDataOutputStream
对Hadoop中数据输出流的统一封装
5）org.apache.hadoop.fs.FSDataInputStream
对Hadoop中数据输入流的统一封装
Java访问HDFS主要编程步骤
1）构建Configuration对象，读取并解析相关配置文件
Configuration conf=new Configuration();
2）设置相关属性
conf.set("fs.defaultFS","hdfs://1IP:9000");
3）获取特定文件系统实例fs（以HDFS文件系统实例）
FileSystem fs=FileSystem.get(new URI("hdfs://IP:9000"),conf,“hdfs");
4）通过文件系统实例fs进行文件操作(以删除文件实例)
fs.delete(new Path("/user/liuhl/someWords.txt"));
示例代码
1、新建mave项目:hadoop-hdfs-demo。
pom.xml如下：
<?xml version="1.0" encoding="UTF-8"?><project xmlns="/POM/4.0.0"xmlns:xsi="/2001/XMLSchema-instance"xsi:schemaLocation="/POM/4.0.0 /xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>com.hadoop.demo</groupId><artifactId>hadoop-hdfs-demo</artifactId><version>1.0-SNAPSHOT</version><dependencies><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-common</artifactId><version>2.8.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-client</artifactId><version>2.8.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-hdfs</artifactId><version>2.8.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-mapreduce-client-core</artifactId><version>2.8.1</version></dependency><dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-auth</artifactId><version>2.8.1</version></dependency><dependency><groupId>log4j</groupId><artifactId>log4j</artifactId><version>1.2.17</version></dependency><dependency><groupId>commons-logging</groupId><artifactId>commons-logging</artifactId><version>1.2</version></dependency><dependency><groupId>org.projectlombok</groupId><artifactId>lombok</artifactId><version>1.16.10</version></dependency></dependencies></project>
2、新建连接hadoop的类：ConnectHadoop
import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FileSystem;import java.io.IOException;import .URI;import .URISyntaxException;public class ConnectHadoop {public static FileSystem getHadoopFileSystem() {FileSystem fs = null;Configuration conf = null;//此时的conf不需任何设置，只需读取远程的配置文件即可conf = new Configuration();// Hadoop的用户名，master机器的登录用户String hdfsUserName = "root";URI hdfsUri = null;try {// HDFS的访问路径hdfsUri = new URI("hdfs://192.168.137.100:9000");} catch (URISyntaxException e) {e.printStackTrace();}try {// 根据远程的NN节点，获取配置信息，创建HDFS对象fs = FileSystem.get(hdfsUri,conf,hdfsUserName);} catch (IOException e) {e.printStackTrace();} catch (InterruptedException e) {e.printStackTrace();}return fs;}}
hdfs://192.168.137.100:9000，是master节点下的core-site.xml的配置
3、测试基本操作类：HadoopHdfsBaseOperation
注意：运行过程中会报以下异常，但是程序可以运行成功，所说是本地要放一个hadoop的二进制包，并且要填写HADOOP_HOME
import lombok.extern.slf4j.Slf4j;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.*;import org.apache.hadoop.io.IOUtils;import java.io.File;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.Iterator;import java.util.Map;@Slf4jpublic class HadoopHdfsBaseOperation {public static void main(String[] args){FileSystem fs = ConnectHadoop.getHadoopFileSystem();try {//createDir(fs);//deleteDir(fs);//renamePath(fs);//iteratorPath(fs,new Path("/aa"));//showAllConf();//printHdfsFileContent(fs);//uploadLocalFileToHdfs(fs);//downloadFileFromHdfs(fs); copyInHdfs(fs);}catch (Exception e){log.error("hdfs error,{}",e);}finally {try {fs.close();} catch (IOException e) {e.printStackTrace();}}}/*** 创建目录* @param fs* @return*/public static void createDir(FileSystem fs){boolean b = false;Path path = new Path("/hzb");try {// even the path exist,it can also create the path. fs.mkdirs(path);log.info("mkdir success");} catch (IOException e) {log.error("mkdir error,{}",e);}}/*** 删除path，参数true相当于rm -r* @param fs* @return*/public static void deleteDir(FileSystem fs){boolean b = false;Path path = new Path("/xxxx/yyyy");try {// even the path exist,it can also create the path.fs.delete(path,true);log.info("delete dir success");} catch (IOException e) {log.error("delete error,{}",e);}}/*** 删除path，参数true相当于rm -r* @param fs* @return*/public static void renamePath(FileSystem fs){boolean b = false;Path oldPath = new Path("/xxxx");Path newPath = new Path("/zzzz");try {// even the path exist,it can also create the path. fs.rename(oldPath,newPath);log.info("rename path success");} catch (IOException e) {log.error("rename error,{}",e);}}/*** 遍历文件夹及子文件* @param hdfs* @return*/public static void iteratorPath(FileSystem hdfs,Path listPath){FileStatus[] files;try {files = hdfs.listStatus(listPath);// 实际上并不是每个文件夹都会有文件的。if(files.length == 0){// 如果不使用toUri()，获取的路径带URL。log.info("==>root dir:{}",listPath.toUri().getPath());}else {// 判断是否为文件for (FileStatus f : files) {if (files.length == 0 || f.isFile()) {log.info("==>file:{}",f.getPath().toUri().getPath());} else {// 是文件夹，且非空，就继续遍历 iteratorPath(hdfs, f.getPath());}}}} catch (IOException e) {log.error("iteratorPath error,{}",e);}}/*** 读取远程hadoop集群的所有配置文件信息，并以键值对打印出来*/public static void showAllConf(){Configuration conf = new Configuration();conf.set("fs.defaultFS", "hdfs://192.168.137.100:9000");Iterator<Map.Entry<String,String>> it = conf.iterator();log.info("==================================================以下是远程hadoop的配置信息==============");while(it.hasNext()){Map.Entry<String,String> entry = it.next();log.info(entry.getKey()+"=" +entry.getValue());}log.info("==================================================以上是远程hadoop的配置信息==============");}/*** 将远程hdfs中的test/readme.txt内容读取并打印到console并输出到E*/public static void printHdfsFileContent(FileSystem hdfs){try {FSDataInputStream is = hdfs.open(new Path("/test/readme.txt"));OutputStream os = new FileOutputStream(new File("E:/hadooptest/readme.txt"));byte[] buff = new byte[1024];int length = 0;log.info("远程的/test/readme.txt内容如下：=======================》");while ((length = is.read(buff)) != -1) {System.out.println(new String(buff, 0, length));os.write(buff, 0, length);os.flush();}} catch (Exception e){log.error("printHdfsFileContent error,{}",e);}}/*** 文件上传,将本地的E:/hadooptest/navicat.zip上传到hdfs的/aa* @param hdfs*/public static void uploadLocalFileToHdfs(FileSystem hdfs){Path HDFSPath = new Path("/aa");Path localPath = new Path("E:/hadooptest/navicat.zip");// 如果上传的路径不存在会创建// 如果该路径文件已存在，就会覆盖try {hdfs.copyFromLocalFile(localPath,HDFSPath);} catch (IOException e) {e.printStackTrace();log.error("uploadLocalFileToHdfs error,{}",e);}}/*** 文件下载,将hdfs中/aa/navicat.zip文件下载到E:/hadooptest/,经过测试直接使用hdfs.copyToLocalFile下载不下来，所有用文件流来下载* @param hdfs*/public static void downloadFileFromHdfs(FileSystem hdfs){// Path HDFSPath = new Path("/aa/navicat.zip");// Path localPath = new Path("E:/hadooptest/");// try {// log.info("====================开始下载=======================");// hdfs.copyToLocalFile(HDFSPath,localPath);// log.info("====================下载结束=======================");// } catch (IOException e) {// e.printStackTrace();// log.error("downloadFileFromHdfs error,{}",e);// }try {FSDataInputStream ifs = hdfs.open(new Path("/aa/navicat.zip"));OutputStream os = new FileOutputStream(new File("E:/hadooptest/navicat.zip"));byte[] buff = new byte[1024];int length = 0;log.info("============开始下载=======================》");while ((length = ifs.read(buff)) != -1) {os.write(buff, 0, length);os.flush();}} catch (Exception e){log.error("printHdfsFileContent error,{}",e);}}/*** 在hdfs内部之间复制文件* 使用FSDataInputStream来打开文件open(Path p)* 使用FSDataOutputStream开创建写到的路径create(Path p)* 使用 IOUtils.copyBytes(FSDataInputStream,FSDataOutputStream,int buffer,Boolean isClose)来进行具体的读写* 说明：* 1.java中使用缓冲区来加速读取文件，这里也使用了缓冲区，但是只要指定缓冲区大小即可，不必单独设置一个新的数组来接受* 2.最后一个布尔值表示是否使用完后关闭读写流。通常是false，如果不手动关会报错的* @param hdfs*/public static void copyInHdfs(FileSystem hdfs){Path inPath = new Path("/aa/navicat.zip");Path outPath = new Path("/test/navicat.zip");FSDataInputStream hdfsIn = null;FSDataOutputStream hdfsOut = null;try {hdfsIn = hdfs.open(inPath);hdfsOut = hdfs.create(outPath);IOUtils.copyBytes(hdfsIn,hdfsOut,1024*1024*64,false);} catch (IOException e) {log.error("copyInHdfs error,{}",e);}}}
