java api 操作 hdfs

文章地址 ：http://www.haha174.top/article/details/255189

1.简介

之前说到了shell 脚本操作hdfs 现在那么本篇文章讲述java 怎么操作hdfs

使用 sh start-dfs.sh 启动 hdfs jps 查看hdfs 状态 确保 hdfs

SecondaryNameNode NameNode DataNode 都已经 启动（如果没有安装hdfs 可以参考这篇 http://blog.csdn.net/u012957549/article/details/78787411）

2.创建工程

使用idea 创建一个maven 工程

编写依赖

<dependencies>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>3.0.0-alpha1</version>
</dependency>

<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
</dependencies>

3. 编写

3.1 before 和after

junit 提供一个 before 和 after 的注解

before 在测试代码 执行之前生效

after 在测试代码执行结束后生效

3.1.1 before 把链接配置 放在 before 中

public static final String HDFS_PATH = "hdfs://192.168.1.223:8020";
FileSystem fileSystem = null;
Configuration configuration = null;

@Before
public void setUp() throws Exception {
System.out.println("HDFSApp.setUp");
configuration = new Configuration();
fileSystem = FileSystem.get(new URI(HDFS_PATH), configuration, "root");
}

使用 这种方法 填入url 和user 获取远程配置

3.1.2 after

@After
public void tearDown() throws Exception {
configuration = null;
fileSystem = null;

System.out.println("HDFSApp.tearDown");
}

3.2 创建HDFS目录

@Test
public void mkdir() throws Exception {
fileSystem.mkdirs(new Path("/hdfsapi/test"));
}

3.3 创建文件

@Test
public void create() throws Exception {
FSDataOutputStream output = fileSystem.create(new Path("/hdfsapi/test/a.txt"));
output.write("hello hadoop".getBytes());
output.flush();
output.close();
}

3.4 查看HDFS文件的内容

@Test
public void cat() throws Exception {
FSDataInputStream in = fileSystem.open(new Path("/hdfsapi/test/a.txt"));
IOUtils.copyBytes(in, System.out, 1024);
in.close();
}

3.5 重命名

@Test
public void rename() throws Exception {
Path oldPath = new Path("/hdfsapi/test/a.txt");
Path newPath = new Path("/hdfsapi/test/b.txt");
fileSystem.rename(oldPath, newPath);
}

3.6 上传文件到HDFS

@Test
public void copyFromLocalFile() throws Exception {
Path localPath = new Path("C:\\Users\\haha174\\Desktop\\work\\mesos.yaml");
Path hdfsPath = new Path("/hdfsapi/test");
fileSystem.copyFromLocalFile(localPath, hdfsPath);
}

3.7 上传文件到HDFS

@Test
public void copyFromLocalFileWithProgress() throws Exception {
InputStream in = new BufferedInputStream(
new FileInputStream(
new File("C:\\haha174\\nginx\\html\\hadoop-3.0.0.tar.gz")));

FSDataOutputStream output = fileSystem.create(new Path("/hdfsapi/test/hadoop-3.0.0.tar.gz"),
new Progressable() {
public void progress() {
System.out.print(".");  //带进度提醒信息
}
});

IOUtils.copyBytes(in, output, 4096);
}

3.8 下载HDFS文件

@Test
public void copyToLocalFile() throws Exception {
Path localPath = new Path("c:/tmp/h.txt");
Path hdfsPath = new Path("/hdfsapi/test/hello.txt");
fileSystem.copyToLocalFile(hdfsPath, localPath);
}

3.9 查看某个目录下的所有文件

@Test
public void listFiles() throws Exception {
FileStatus[] fileStatuses = fileSystem.listStatus(new Path("/"));

for(FileStatus fileStatus : fileStatuses) {
String isDir = fileStatus.isDirectory() ? "文件夹" : "文件";
short replication = fileStatus.getReplication();
long len = fileStatus.getLen();
String path = fileStatus.getPath().toString();

System.out.println(isDir + "\t" + replication + "\t" + len + "\t" + path);
}

3.10 删除

@Test
public void delete() throws Exception{
fileSystem.delete(new Path("/"), true);
}