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JAVA连接HDFS使用案例

一、引言

Hadoop分布式文件系统（HDFS）是大数据存储的基础。对于Java开发者来说，能够通过Java代码操作HDFS是处理大数据任务的关键技能。本文将通过几个简单的示例，展示如何使用Java连接HDFS并执行一些基本的文件操作。

二、连接HDFS

1、第一步：添加依赖

在Maven项目中，需要添加Hadoop客户端依赖：

<dependency><groupId>org.apache.hadoop</groupId><artifactId>hadoop-client</artifactId><version>2.8.2</version>
</dependency>

2、第二步：创建连接

创建HDFS连接的基本代码如下：

Configuration conf = new Configuration();
FileSystem fs = FileSystem.get(new URI("hdfs://localhost:9000"), conf);

三、操作HDFS

1、检查文件是否存在

public static boolean test(Configuration conf, String path) {try (FileSystem fs = FileSystem.get(conf)) {return fs.exists(new Path(path));} catch (IOException e) {e.printStackTrace();return false;}
}

2、在文件开头或末尾插入内容

public static void insertContent(String filePath, String content, boolean insertAtBeginning) throws URISyntaxException {try {Configuration conf = new Configuration();FileSystem fs = FileSystem.get(new URI("hdfs://localhost:9000"), conf);Path path = new Path(filePath);if (fs.exists(path)) {BufferedReader reader = new BufferedReader(new InputStreamReader(fs.open(path)));StringBuilder originalContent = new StringBuilder();String line;while ((line = reader.readLine()) != null) {originalContent.append(line).append("\n");}reader.close();FSDataOutputStream outputStream = fs.create(path, true);if (insertAtBeginning) {outputStream.write(content.getBytes());outputStream.write(originalContent.toString().getBytes());} else {outputStream.write(originalContent.toString().getBytes());outputStream.write(content.getBytes());}outputStream.close();} else {FSDataOutputStream outputStream = fs.create(path);outputStream.write(content.getBytes());outputStream.close();}} catch (IOException e) {e.printStackTrace();}
}

3、删除文件

public static void main(String[] args) throws IOException, URISyntaxException {Configuration conf = new Configuration();FileSystem fs = FileSystem.get(new URI("hdfs://localhost:9000"), conf);String name = "hdfs://localhost:9000/a/a.txt";boolean res = fs.delete(new Path(name), false);if (res) {System.out.println("File deleted successfully.");} else {System.out.println("File deletion failed.");}
}

4、移动文件

public static void moveFile(String sourcePath, String destinationPath) {try {Configuration conf = new Configuration();FileSystem fs = FileSystem.get(new URI("hdfs://localhost:9000"), conf);Path src = new Path(sourcePath);Path dst = new Path(destinationPath);if (!fs.exists(src)) {System.out.println("Source file does not exist.");return;}if (!fs.exists(dst.getParent())) {fs.mkdirs(dst.getParent());}boolean success = fs.rename(src, dst);if (success) {System.out.println("File moved successfully.");} else {System.out.println("File move failed.");}} catch (Exception e) {e.printStackTrace();}
}

四、总结

通过上述示例，我们可以看到Java连接HDFS并执行基本文件操作的过程相对直接。这些操作包括检查文件是否存在、在文件开头或末尾插入内容、删除文件以及移动文件。掌握这些基本操作对于处理大数据任务至关重要。