Hadoop 的版本是 3.1.1
1. 启动 Hadoop 服务
$ start-all.sh
2. 新建 IDEA 的 Maven 项目
2.1 选中 Maven，Project SDK 选择为 1.8，再点击 Next
点击 Next
2.2 填写好 GroupId，ArtifactId 后，点击 Next
2.3 点击 Finish
image.png
3. 修改 Target bytecode version
打开 Setting，选中 Build, Execution, Deployment -> Compiler -> java，将 Target bytecode version 改为 1.8 或 8。
Target bytecode version
确认这几个配置下的 jdk 版本都为 1.8
Project SDK
Module SDK
4. 导入需要的 jar 包
4.1 选中 Dependencies 后点击下方的 + 号，选择「JARs or directories」
添加 jar 包
JARs or directories
4.2 进入 Hadoop 目录下的 share/hadoop/ 中，把这几个包都导进去
share/hadoop/
选择 OK
继续 OK
4.2 在 pom.xml 中添加如下依赖
<dependencies>
<!-- https://mvnrepository.com/artifact/junit/junit -->
<dependency>
<groupId>junit</groupId>
<artifactId>junit</artifactId>
<version>4.12</version>
<scope>test</scope>
</dependency>
<!--<!– https://mvnrepository.com/artifact/commons-logging/commons-logging –>-->
<dependency>
<groupId>commons-logging</groupId>
<artifactId>commons-logging</artifactId>
<version>1.2</version>
</dependency>
<!--<!– https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-common –>-->
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-common</artifactId>
<version>3.1.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-core -->
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-core</artifactId>
<version>1.2.1</version>
</dependency>
<!-- https://mvnrepository.com/artifact/org.apache.hadoop/hadoop-hdfs -->
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-hdfs</artifactId>
<version>3.1.1</version>
</dependency>
<dependency>
<groupId>org.apache.hadoop</groupId>
<artifactId>hadoop-client</artifactId>
<version>3.1.1</version>
</dependency>
</dependencies>
5. 编写 Hadoop 项目的 Java 代码
5.1 新建 Java 类「Test.java」
image.png
5.2 编写代码
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.FileSystem;
import org.apache.hadoop.fs.Path;
import java.io.IOException;
import java.net.URI;
import java.net.URISyntaxException;
public class Test {
// 在 HDFS 中新建一个 test 文件夹
public static void main(String[] args) {
FileSystem fileSystem = null;
try {
fileSystem = FileSystem.get(new URI("hdfs://localhost:9000/"),new Configuration(),"binguner");
fileSystem.mkdirs(new Path("/test"));
fileSystem.close();
} catch (IOException e) {
e.printStackTrace();
} catch (InterruptedException e) {
e.printStackTrace();
} catch (URISyntaxException e) {
e.printStackTrace();
}
}
}
5.3 运行 Java 程序
image.png
6. 运行结果
6.1 运行前的 HDFS 目录下没有 test 文件夹
6.2 运行后的 HDFS 目录下多了 test 文件夹
7. FileSystem 常用接口
- 7.1
mkdirs
public boolean mkdirs(Path f) throws IOException {
return this.mkdirs(f, FsPermission.getDirDefault());
}
参数是新的文件夹的路径，可以在文件夹里嵌套文件夹进行创建。
- 7.2
create
public FSDataOutputStream create(Path f) throws IOException {
return this.create(f, true);
}
public FSDataOutputStream create(Path f, boolean overwrite) throws IOException {
return this.create(f, overwrite, this.getConf().getInt("io.file.buffer.size", 4096), this.getDefaultReplication(f), this.getDefaultBlockSize(f));
}
public FSDataOutputStream create(Path f, Progressable progress) throws IOException {
return this.create(f, true, this.getConf().getInt("io.file.buffer.size", 4096), this.getDefaultReplication(f), this.getDefaultBlockSize(f), progress);
}
public FSDataOutputStream create(Path f, short replication) throws IOException {
return this.create(f, true, this.getConf().getInt("io.file.buffer.size", 4096), replication, this.getDefaultBlockSize(f));
}
public FSDataOutputStream create(Path f, short replication, Progressable progress) throws IOException {
return this.create(f, true, this.getConf().getInt("io.file.buffer.size", 4096), replication, this.getDefaultBlockSize(f), progress);
}
public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize) throws IOException {
return this.create(f, overwrite, bufferSize, this.getDefaultReplication(f), this.getDefaultBlockSize(f));
}
public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, Progressable progress) throws IOException {
return this.create(f, overwrite, bufferSize, this.getDefaultReplication(f), this.getDefaultBlockSize(f), progress);
}
public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, short replication, long blockSize) throws IOException {
return this.create(f, overwrite, bufferSize, replication, blockSize, (Progressable)null);
}
public FSDataOutputStream create(Path f, boolean overwrite, int bufferSize, short replication, long blockSize, Progressable progress) throws IOException {
return this.create(f, FsCreateModes.applyUMask(FsPermission.getFileDefault(), FsPermission.getUMask(this.getConf())), overwrite, bufferSize, replication, blockSize, progress);
}
public abstract FSDataOutputStream create(Path var1, FsPermission var2, boolean var3, int var4, short var5, long var6, Progressable var8) throws IOException;
public FSDataOutputStream create(Path f, FsPermission permission, EnumSet<CreateFlag> flags, int bufferSize, short replication, long blockSize, Progressable progress) throws IOException {
return this.create(f, permission, flags, bufferSize, replication, blockSize, progress, (ChecksumOpt)null);
}
public FSDataOutputStream create(Path f, FsPermission permission, EnumSet<CreateFlag> flags, int bufferSize, short replication, long blockSize, Progressable progress, ChecksumOpt checksumOpt) throws IOException {
return this.create(f, permission, flags.contains(CreateFlag.OVERWRITE), bufferSize, replication, blockSize, progress);
}
create 有多个重载函数，它的参数可以指定是否覆盖已有的文件、文件备份数量、写入文件缓冲区大小、文件块大小以及文件权限。它的返回值是一个 FSDataOutputStream，通过返回的 FSDataOutputStream 对象可以对文件进行写入。
- 7.3
copyFromLocal
public void copyFromLocalFile(Path src, Path dst) throws IOException {
this.copyFromLocalFile(false, src, dst);
}
public void copyFromLocalFile(boolean delSrc, Path src, Path dst) throws IOException {
this.copyFromLocalFile(delSrc, true, src, dst);
}
public void copyFromLocalFile(boolean delSrc, boolean overwrite, Path[] srcs, Path dst) throws IOException {
Configuration conf = this.getConf();
FileUtil.copy(getLocal(conf), srcs, this, dst, delSrc, overwrite, conf);
}
将本地文件拷贝到文件系统，参数可以指定上传本地文件的路径，上传的多个路径组成的 Path 数组，存放目标对路径，可以指定是否删除本地本地的文件或者覆盖 hdfs 上已经创建的文件。
- 7.4
copyToLocalFile
public void copyToLocalFile(Path src, Path dst) throws IOException {
this.copyToLocalFile(false, src, dst);
}
public void copyToLocalFile(boolean delSrc, Path src, Path dst) throws IOException {
this.copyToLocalFile(delSrc, src, dst, false);
}
将目标文件复制到本地指定路径，delSrc 参数指定移动文件后是否要删除源文件。
- 7.6
moveToLocalFile
public void moveToLocalFile(Path src, Path dst) throws IOException {
this.copyToLocalFile(true, src, dst);
}
将目标文件移动到指定路径，函数内部调用的是 copyToLocalFile。
- 7.6
exists
public boolean exists(Path f) throws IOException {
try {
return this.getFileStatus(f) != null;
} catch (FileNotFoundException var3) {
return false;
}
}
输入一个路径，检查 HDFS 上是否存在这个路径，存在返回 true，不存在返回 false。
- 7.7
delete
public abstract boolean delete(Path var1, boolean var2) throws IOException;
第一个参数是要删除的路径，第二个参数为 true 时，如果目标文件夹内有文件，会强制删除。
