从HDFS读取文件时出现MalformedURLException

Question

我有以下测试程序从HDFS读取文件。

public class FileReader {
    public static final String NAMENODE_IP = "172.32.17.209";
    public static final String FILE_PATH = "/notice.html";

    public static void main(String[] args) throws MalformedURLException,
            IOException {
        String url = "hdfs://" + NAMENODE_IP + FILE_PATH;

        InputStream is = new URL(url).openStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        String line = br.readLine();
        while(line != null) {
            System.out.println(line);
            line = br.readLine();
        }
    }
}

它给出了java.net.MalformedURLException

Exception in thread "main" java.net.MalformedURLException: unknown protocol: hdfs
    at java.net.URL.<init>(URL.java:592)
    at java.net.URL.<init>(URL.java:482)
    at java.net.URL.<init>(URL.java:431)
    at in.ksharma.hdfs.FileReader.main(FileReader.java:29)

Answer 1

注册Hadoop的Url处理程序。 标准URL处理程序将不知道如何处理hdfs：//方案。

试试这个：

public static void main(String[] args) throws MalformedURLException,
            IOException {
        URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory());

        String url = "hdfs://" + NAMENODE_IP + FILE_PATH;

        InputStream is = new URL(url).openStream();
        InputStreamReader isr = new InputStreamReader(is);
        BufferedReader br = new BufferedReader(isr);
        String line = br.readLine();
        while(line != null) {
            System.out.println(line);
            line = br.readLine();
        }
    }

Answer 2

在编写用于从hadoop 2.6上的hdfs读取的Java应用程序时，我遇到了同样的问题。 我的解决方案是：添加

 hadoop-2.X/share/hadoop/hdfs/hadoop-hdfs-2.X.jar to your classpath.

Answer 3

在我们的例子中，我们必须将它与其他答案结合起来：
https://stackoverflow.com/a/21118824/1549135

首先在我们的HDFS安装类 （ Scala code ）中：

val hadoopConfig: Configuration = new Configuration()
hadoopConfig.set("fs.hdfs.impl", classOf[DistributedFileSystem].getName)
hadoopConfig.set("fs.file.impl", classOf[LocalFileSystem].getName)

后来，就像在接受的答案中一样：
https://stackoverflow.com/a/25971334/1549135

URL.setURLStreamHandlerFactory(new FsUrlStreamHandlerFactory)
Try(new URL(path))

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边注：

我们已经有了： "org.apache.hadoop" % "hadoop-hdfs" % "2.8.0"在我们的依赖项中并没有帮助。