1.17总结

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

• 判断路径是否存在
  /
  public static boolean test(Configuration conf, String path) throws IOException {
  FileSystem fs = FileSystem.get(conf);
  return fs.exists(new Path(path));
  }
  /*
• 复制文件到指定路径
• 若路径已存在，则进行覆盖
  /
  public static void copyFromLocalFile(Configuration conf, String localFilePath, String
  remoteFilePath) throws IOException {
  FileSystem fs = FileSystem.get(conf);
  Path localPath = new Path(localFilePath);
  Path remotePath = new Path(remoteFilePath);
  / fs.copyFromLocalFile 第一个参数表示是否删除源文件，第二个参数表示是否覆
  盖 /
  fs.copyFromLocalFile(false, true, localPath, remotePath);
  fs.close();
  }
  /*
• 追加文件内容
  /
  public static void appendToFile(Configuration conf, String localFilePath, String
  remoteFilePath) throws IOException {
  FileSystem fs = FileSystem.get(conf);
  Path remotePath = new Path(remoteFilePath);
  / 创建一个文件读入流 /
  FileInputStream in = new FileInputStream(localFilePath);
  / 创建一个文件输出流，输出的内容将追加到文件末尾 /
  FSDataOutputStream out = fs.append(remotePath);
  / 读写文件内容 */
  byte[] data = new byte[1024];
  int read = -1;
  while ( (read = in.read(data)) > 0 ) {
  out.write(data, 0, read);
  }
  out.close();
  in.close();
  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:\local.txt"; // 本地路径
  String remoteFilePath = "/user/root/text.txt"; // HDFS 路径
  String choice = "append"; // 若文件存在则追加到文件末尾
  // String choice = "overwrite"; // 若文件存在则覆盖
  try {
  / 判断文件是否存在 /
  Boolean fileExists = false;
  if (HDFSApi.test(conf, remoteFilePath)) {
  fileExists = true;
  System.out.println(remoteFilePath + " 已存在.");
  } else {
  System.out.println(remoteFilePath + " 不存在.");
  }
  / 进行处理 */
  if ( !fileExists) { // 文件不存在，则上传
  HDFSApi.copyFromLocalFile(conf, localFilePath, remoteFilePath);
  System.out.println(localFilePath + " 已上传至 " + remoteFilePath);
  } else if ( choice.equals("overwrite") ) { // 选择覆盖
  HDFSApi.copyFromLocalFile(conf, localFilePath, remoteFilePath);
  System.out.println(localFilePath + " 已覆盖 " + remoteFilePath);
  } else if ( choice.equals("append") ) { // 选择追加
  HDFSApi.appendToFile(conf, localFilePath, remoteFilePath);
  System.out.println(localFilePath + " 已追加至 " + remoteFilePath);
  }
  } catch (Exception e) {
  e.printStackTrace();
  }
  }
  }
  log4j.properties
  log4j.rootLogger=info,consolePrint,errorFile,logFile

log4j.appender.consolePrint.Encoding = UTF-8
log4j.appender.consolePrint = org.apache.log4j.ConsoleAppender
log4j.appender.consolePrint.Target = System.out
log4j.appender.consolePrint.layout = org.apache.log4j.PatternLayout
log4j.appender.consolePrint.layout.ConversionPattern=%d %p [%c] - %m%n

log4j.appender.logFile.Encoding = UTF-8
log4j.appender.logFile = org.apache.log4j.DailyRollingFileAppender
log4j.appender.logFile.File = D:/eclipse/log4j_properties_runlog/WorldCount_demo_run.log
log4j.appender.logFile.Append = true
log4j.appender.logFile.Threshold = info
log4j.appender.logFile.layout = org.apache.log4j.PatternLayout
log4j.appender.logFile.layout.ConversionPattern = %-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n

log4j.appender.errorFile.Encoding = UTF-8
log4j.appender.errorFile = org.apache.log4j.DailyRollingFileAppender
log4j.appender.errorFile.File = D:/eclipse/log4j_properties_runlog/WorldCount_demo_error.log
log4j.appender.errorFile.Append = true
log4j.appender.errorFile.Threshold = ERROR
log4j.appender.errorFile.layout = org.apache.log4j.PatternLayout
log4j.appender.errorFile.layout.ConversionPattern =%-d{yyyy-MM-dd HH:mm:ss} [ %t:%r ] - [ %p ] %m%n
· 运行截图

（2）从HDFS中下载指定文件，如果本地文件与要下载的文件名称相同，则自动对下载的文件重命名；
shell命令
if $(hdfsdfs-test-efile:///root/text.txt);then$(hdfs dfs -copyToLocal text.txt ./text2.txt);
else $(hdfs dfs -copyToLocal text.txt ./text.txt);
Fi