大数据技术连载-03-2-大数据的存储-Hadoop的HDFS的读写-JavaApi

读数据

        import java.io.BufferedReader;
        import java.io.InputStreamReader;
 
        import org.apache.hadoop.conf.Configuration;
        import org.apache.hadoop.fs.FileSystem;
        import org.apache.hadoop.fs.Path;
        import org.apache.hadoop.fs.FSDataInputStream;
 
        public class Chapter3 {
                public static void main(String[] args) {
                        try {
                                Configuration conf = new Configuration();
                                conf.set("fs.defaultFS","hdfs://localhost:9000");
                                conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");
                                FileSystem fs = FileSystem.get(conf);
                                Path file = new Path("test"); 
                                FSDataInputStream getIt = fs.open(file);
                                BufferedReader d = new BufferedReader(new InputStreamReader(getIt));
                                String content = d.readLine(); //读取文件一行
                                System.out.println(content);
                                d.close(); //关闭文件
                                fs.close(); //关闭hdfs
                        } catch (Exception e) {
                                e.printStackTrace();
                        }
                }
        }
　　

 

 

 

写数据

        import org.apache.hadoop.conf.Configuration;  
        import org.apache.hadoop.fs.FileSystem;
        import org.apache.hadoop.fs.FSDataOutputStream;
        import org.apache.hadoop.fs.Path;
 
        public class Chapter3 {    
                public static void main(String[] args) { 
                        try {
                                Configuration conf = new Configuration();  
                                conf.set("fs.defaultFS","hdfs://localhost:9000");
                                conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");
                                FileSystem fs = FileSystem.get(conf);
                                byte[] buff = "Hello world".getBytes(); // 要写入的内容
                                String filename = "test"; //要写入的文件名
                                FSDataOutputStream os = fs.create(new Path(filename));
                                os.write(buff,0,buff.length);
                                System.out.println("Create:"+ filename);
                                os.close();
                                fs.close();
                        } catch (Exception e) {  
                                e.printStackTrace();  
                        }  
                }  
        }

判断文件是否存在

        import org.apache.hadoop.conf.Configuration;
        import org.apache.hadoop.fs.FileSystem;
        import org.apache.hadoop.fs.Path;
 
        public class Chapter3 {
                public static void main(String[] args) {
                            try {
                                    String filename = "test";
 
                                    Configuration conf = new Configuration();
                                    conf.set("fs.defaultFS","hdfs://localhost:9000");
                                    conf.set("fs.hdfs.impl","org.apache.hadoop.hdfs.DistributedFileSystem");
                                    FileSystem fs = FileSystem.get(conf);
                                    if(fs.exists(new Path(filename))){
                                            System.out.println("文件存在");
                                    }else{
                                            System.out.println("文件不存在");
                                    }
                                    fs.close();
                        } catch (Exception e) {
                                e.printStackTrace();
                        }
                }
        }