1.16总结

Java代码
package HDFSApi;

import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.;
import java.io.;
public class HDFSApi {
/**

• 下载文件到本地

• 判断本地路径是否已存在，若已存在，则自动进行重命名
  /
  public static void copyToLocal(Configuration conf, String remoteFilePath, String
  localFilePath) throws IOException {
  FileSystem fs = FileSystem.get(conf);
  Path remotePath = new Path(remoteFilePath);
  File f = new File(localFilePath);
  / 如果文件名存在，自动重命名(在文件名后面加上 0, 1 ...) */
  if (f.exists()) {
  System.out.println(localFilePath + " 已存在.");
  Integer i = 0;
  while (true) {
  f = new File(localFilePath + "" + i.toString());
  if (!f.exists()) {
  localFilePath = localFilePath + "" + i.toString();
  break;
  }
  }
  System.out.println("将重新命名为: " + localFilePath);
  }

  // 下载文件到本地
  Path localPath = new Path(localFilePath);
  fs.copyToLocalFile(remotePath, localPath);
  fs.close();
  }

/**

• 主函数
  */
  public static void main(String[] args) {
  Configuration conf = new Configuration();
  conf.set("fs.default.name","hdfs://node1:8020");
  String localFilePath = "E:/text.txt"; // 本地路径
  String remoteFilePath = "/user/root/text.txt"; // HDFS 路径
  try {
  HDFSApi.copyToLocal(conf, remoteFilePath, localFilePath);
  System.out.println("下载完成");
  } catch (Exception e) {
  e.printStackTrace();
  }
  }
  }

运行结果

（3）将HDFS中指定文件的内容输出到终端中；

java代码
package HDFSApi;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.fs.;
import java.io.;
public class HDFSApi {
/**

• 读取文件内容
  */
  public static void cat(Configuration conf, String remoteFilePath) throws IOException {
  FileSystem fs = FileSystem.get(conf);
  Path remotePath = new Path(remoteFilePath);
  FSDataInputStream in = fs.open(remotePath);
  BufferedReader d = new BufferedReader(new InputStreamReader(in));
  String line = null;
  while ( (line = d.readLine()) != null ) {
  System.out.println(line);
  }
  d.close();
  in.close();
  fs.close();
  }