Java API操作HA方式下的Hadoop

通过java api连接Hadoop集群时，如果集群支持HA方式，那么可以通过如下方式设置来自动切换到活动的master节点上。其中，ClusterName 是可以任意指定的，跟集群配置无关，dfs.ha.namenodes.ClusterName也可以任意指定名称，有几个master就写几个，后面根据相应的设置添加master节点地址即可。

private static String ClusterName = "nsstargate";
    private static final String HADOOP_URL = "hdfs://"+ClusterName;
    public static Configuration conf;

    static {
        conf = new Configuration();
        conf.set("fs.defaultFS", HADOOP_URL);
        conf.set("dfs.nameservices", ClusterName);
        conf.set("dfs.ha.namenodes."+ClusterName, "nn1,nn2");
        conf.set("dfs.namenode.rpc-address."+ClusterName+".nn1", "172.16.50.24:8020");
        conf.set("dfs.namenode.rpc-address."+ClusterName+".nn2", "172.16.50.21:8020");
        //conf.setBoolean(name, value);
        conf.set("dfs.client.failover.proxy.provider."+ClusterName, 
                "org.apache.hadoop.hdfs.server.namenode.ha.ConfiguredFailoverProxyProvider");
    }

上传文件到HDFS的代码如下，至于读取等其他操作，可以参考网络上其他文章。

/**
     * 上传文件到HDFS上去
     */
    private static void uploadToHdfs() throws IOException {
        String localSrc = "E:\test\article01.txt";
        String dst = "/user/test/article04.txt";
        FileSystem fs = FileSystem.get(URI.create(HADOOP_URL), conf);
        long start = new Date().getTime();

       /* InputStream in = new FileInputStream(localSrc);
        InputStreamReader isr = new InputStreamReader(in, "GBK");
        OutputStream out = fs.create(new Path(HADOOP_URL+dst), true);
        IOUtils.copy(isr, out, "UTF8");*/
        
        //该方法更快
        FSDataOutputStream outputStream=fs.create(new Path(dst));
        String fileContent = FileUtils.readFileToString(new File(localSrc), "GBK");
        outputStream.write(fileContent.getBytes());
        outputStream.close();
        
        long end = new Date().getTime();
        System.out.println("use:"+(end-start));
        
    }