java 操作上传下载 HDFS：could only be replicated to 0 nodes instead of minReplication (=1). There are 1 da-优快云博客

在阿里云服务器上使用Java操作HDFS时遇到了'could only be replicated to 0 nodes instead of minReplication (=1)'的问题。环境为Hadoop 2.9.0的伪分布模式，Java版本1.8。错误出现在上传或下载文件时。解决方案包括检查防火墙设置，确保其未影响HDFS，以及在代码中添加特定配置行以解决可能的复制问题。若下载时同样遇到问题，应首先排除其他可能原因，如DataNode未启动等。

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环境

阿里云服务器
伪分布模式
版本：2.9.0，java 1.8
配置：http://blog.youkuaiyun.com/u012453843/article/details/52431742

代码

//上传文件
public static void main(String[] args) throws Exception {
        Configuration configuration = new Configuration();
        //123.56.xxx.xxx 为阿里云服务器公网 IP
        FileSystem fs = FileSystem.get(URI.create("hdfs://123.56.xxx.xxx:9000/text.txt"), configuration, "root");
        InputStream in = new FileInputStream("D://hdfs_demo1/123.txt");
        OutputStream outputStream = fs.create(new Path("hdfs://123.56.xxx.xxx:9000/text.txt"), new Progressable() {
            public void progress() {
                System.out.print(".");
            }
        });
        IOUtils.copyBytes(in, outputStream, 4096, true);
    }

出现错误

Exception in thread "main" org.apache.hadoop.ipc.RemoteException(java.io.IOException): File /text.txt could only be replicated to 0 nodes instead of minReplication (=1).  There are 1 datanode(s) running and 1 node(s) are excluded in this operation.
    at org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1797)
    at org.apache.hadoop.hdfs.server.namenode.FSDirWriteFileOp.chooseTargetForNewBlock(FSDirWriteFileOp.java:265)
    at org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:2559)
    at org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:846)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:510)
    at org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:503)
    at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:989)
    at org.apache.hadoop.ipc.Server$RpcCall.run(Server.java:868)
    at org.apache.hadoop.ipc.Server$RpcCall.run(Server.java:814)
    at java.security.AccessController.doPrivileged(Native Method)
    at javax.security.auth.Subject.doAs(Subject.java:422)
    at org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1886)
    at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2603)

    at org.apache.hadoop.ipc.Client.getRpcResponse(Client.java:1493)
    at org.apache.hadoop.ipc.Client.call(Client.java:1439)
    at org.apache.hadoop.ipc.Client.call(Client.java:1349)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:227)
    at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:116)
    at com.sun.proxy.$Proxy10.addBlock(Unknown Source)
    at org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolTranslatorPB.addBlock(ClientNamenodeProtocolTranslatorPB.java:444)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:422)
    at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeMethod(RetryInvocationHandler.java:165)
    at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invoke(RetryInvocationHandler.java:157)
    at org.apache.hadoop.io.retry.RetryInvocationHandler$Call.invokeOnce(RetryInvocationHandler.java:95)
    at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:359)
    at com.sun.proxy.$Proxy11.addBlock(Unknown Source)
    at org.apache.hadoop.hdfs.DataStreamer.locateFollowingBlock(DataStreamer.java:1845)
    at org.apache.hadoop.hdfs.DataStreamer.nextBlockOutputStream(DataStreamer.java:1645)
    at org.apache.hadoop.hdfs.DataStreamer.run(DataStreamer.java:710)

解决方法

防火墙关闭（我没有这个问题，但是很多人这个会影响）
添加 configuration.set("dfs.client.use.datanode.hostname", "true");这句代码
如果下载也出现问题如 org.apache.hadoop.hdfs.BlockMissingException: Could not obtain block: BP-115793501-172.17.162.27-1512710701892:blk_1073741825_1001 file=/hdfs.xml ，确定排除网上其他什么原因（datanode 没有启动之类的），也可以添加上面那行代码尝试。