总结： 之前在教材上看hdfs的Java客户端编写，只有关键代码，呵呵……。闲话不说，上正文。
1. Hadoop 的Java客户端编写建议在linux系统上开发
2. 可以使用eclipse,idea 等IDE工具，目前比较流行的是idea
3. 新建项目之后需要添加很多jar包，win，linux下添加jar方式略有不同
4. 使用代码会出现文件格式不认识，权限等问题。
具体：
1.首先测试从hdfs中下载文件:
下载文件的代码:(将hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz文件下载到本地/opt/download/doload.tgz)
package cn.qlq.hdfs;import java.io.FileOutputStream;import java.io.IOException;import org.apache.commons.compress.utils.IOUtils;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.Path;public class HdfsUtil { public static void main(String a[]) throws IOException { //to upload a file Configuration conf = new Configuration(); FileSystem fs = FileSystem.get(conf); Path path = new Path("hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz"); FSDataInputStream input = fs.open(path); FileOutputStream output = new FileOutputStream("/opt/download/doload.tgz"); IOUtils.copy(input, output); }} 直接运行报错:
原因是程序不认识 hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz 这样的目录
log4j:WARN No appenders could be found for logger (org.apache.hadoop.metrics2.lib.MutableMetricsFactory).log4j:WARN Please initialize the log4j system properly.log4j:WARN See http://logging.apache.org/log4j/1.2/faq.html#noconfig for more info.Exception in thread "main" java.lang.IllegalArgumentException: Wrong FS: hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz, expected: file:/// at org.apache.hadoop.fs.FileSystem.checkPath(FileSystem.java:643) at org.apache.hadoop.fs.RawLocalFileSystem.pathToFile(RawLocalFileSystem.java:79) at org.apache.hadoop.fs.RawLocalFileSystem.deprecatedGetFileStatus(RawLocalFileSystem.java:506) at org.apache.hadoop.fs.RawLocalFileSystem.getFileLinkStatusInternal(RawLocalFileSystem.java:724) at org.apache.hadoop.fs.RawLocalFileSystem.getFileStatus(RawLocalFileSystem.java:501) at org.apache.hadoop.fs.FilterFileSystem.getFileStatus(FilterFileSystem.java:397) at org.apache.hadoop.fs.ChecksumFileSystem$ChecksumFSInputChecker.(ChecksumFileSystem.java:137) at org.apache.hadoop.fs.ChecksumFileSystem.open(ChecksumFileSystem.java:339) at org.apache.hadoop.fs.FileSystem.open(FileSystem.java:764) at cn.qlq.hdfs.HdfsUtil.main(HdfsUtil.java:21)
解决办法:
- 第一种: 将hadoop安装目录下的etc目录中的core-site.xml拷贝到eclipse的src目录下。这样就不会报错
运行结果:
[root@localhost download]# lltotal 140224-rw-r--r--. 1 root root 143588167 Apr 20 05:55 doload.tgz[root@localhost download]# pwd/opt/download[root@localhost download]# lltotal 140224-rw-r--r--. 1 root root 143588167 Apr 20 05:55 doload.tgz
- 第二种:直接在程序中修改
我们先查看hdfs-site.xml中的内容:
fs.defaultFS hdfs://localhost:9000 hadoop.tmp.dir /opt/hadoop/hadoop-2.4.1/data/
代码改为:
public static void main(String a[]) throws IOException { //to upload a filed Configuration conf = new Configuration(); //set hdfs root dir conf.set("fs.defaultFS", "hdfs://localhost:9000"); FileSystem fs = FileSystem.get(conf); Path path = new Path("hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz"); FSDataInputStream input = fs.open(path); FileOutputStream output = new FileOutputStream("/opt/download/doload.tgz"); IOUtils.copy(input, output); }
2.下面代码演示了hdfs的基本操作:
package cn.qlq.hdfs;import java.io.FileInputStream;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.net.URI;import java.net.URISyntaxException;import org.apache.commons.compress.utils.IOUtils;import org.apache.hadoop.conf.Configuration;import org.apache.hadoop.fs.FSDataInputStream;import org.apache.hadoop.fs.FSDataOutputStream;import org.apache.hadoop.fs.FileStatus;import org.apache.hadoop.fs.FileSystem;import org.apache.hadoop.fs.LocatedFileStatus;import org.apache.hadoop.fs.Path;import org.apache.hadoop.fs.RemoteIterator;import org.junit.Before;import org.junit.Test;public class HdfsUtil { private FileSystem fs = null; @Before public void befor() throws IOException, InterruptedException, URISyntaxException{ //读取classpath下的xxx-site.xml 配置文件，并解析其内容，封装到conf对象中 Configuration conf = new Configuration(); //也可以在代码中对conf中的配置信息进行手动设置，会覆盖掉配置文件中的读取的值 conf.set("fs.defaultFS", "hdfs://localhost:9000/"); //根据配置信息，去获取一个具体文件系统的客户端操作实例对象 fs = FileSystem.get(new URI("hdfs://localhost:9000/"),conf,"root"); } /** * 上传文件，比较底层的写法 * * @throws Exception */ @Test public void upload() throws Exception { Path dst = new Path("hdfs://localhost:9000/aa/qingshu.txt"); FSDataOutputStream os = fs.create(dst); FileInputStream is = new FileInputStream("/opt/download/haha.txt"); IOUtils.copy(is, os); } /** * 上传文件，封装好的写法 * @throws Exception * @throws IOException */ @Test public void upload2() throws Exception, IOException{ fs.copyFromLocalFile(new Path("/opt/download/haha.txt"), new Path("hdfs://localhost:9000/aa/qingshu2.txt")); } /** * download file * @throws IOException */ @Test public void download() throws IOException { Path path = new Path("hdfs://localhost:9000/jdk-7u65-linux-i586.tar.gz"); FSDataInputStream input = fs.open(path); FileOutputStream output = new FileOutputStream("/opt/download/doload.tgz"); IOUtils.copy(input, output); } /** * 下载文件 * @throws Exception * @throws IllegalArgumentException */ @Test public void download2() throws Exception { fs.copyToLocalFile(new Path("hdfs://localhost:9000/aa/qingshu2.txt"), new Path("/opt/download/haha2.txt")); } /** * 查看文件信息 * @throws IOException * @throws IllegalArgumentException * @throws FileNotFoundException * */ @Test public void listFiles() throws FileNotFoundException, IllegalArgumentException, IOException { // listFiles列出的是文件信息，而且提供递归遍历 RemoteIterator files = fs.listFiles(new Path("/"), true); while(files.hasNext()){ LocatedFileStatus file = files.next(); Path filePath = file.getPath(); String fileName = filePath.getName(); System.out.println(fileName); } System.out.println("---------------------------------"); //listStatus 可以列出文件和文件夹的信息，但是不提供自带的递归遍历 FileStatus[] listStatus = fs.listStatus(new Path("/")); for(FileStatus status: listStatus){ String name = status.getPath().getName(); System.out.println(name + (status.isDirectory()?" is dir":" is file")); } } /** * 创建文件夹 * @throws Exception * @throws IllegalArgumentException */ @Test public void mkdir() throws IllegalArgumentException, Exception { fs.mkdirs(new Path("/aaa/bbb/ccc")); } /** * 删除文件或文件夹 * @throws IOException * @throws IllegalArgumentException */ @Test public void rm() throws IllegalArgumentException, IOException { fs.delete(new Path("/aa"), true); } }