JSch get（）失败，返回NullPointerException

Question

我有一台Jax-RS服务器，它应该保留可通过ssh访问的文件列表，然后我可以通过HTTP下载或流式传输。

我一直在尝试阅读JSch的SFTP频道的文件，但我不断收到NullPointerException。

这里的MessageBodyWriter我写道：

@Provider 
@Produces("video/*") 
public class MediaBodyWriter implements MessageBodyWriter<MediaFile> { 

    @Override 
    public long getSize(MediaFile mFile, Class<?> arg1, Type arg2, Annotation[] arg3, MediaType arg4) { 
     return mFile.getFileSize(); 
    } 

    @Override 
    public boolean isWriteable(Class<?> type, Type arg1, Annotation[] arg2, MediaType arg3) { 
     return type.equals(MediaFile.class); 
    } 

    @Override 
    public void writeTo(MediaFile mFile, 
        Class<?> type, 
        Type genericType, 
        Annotation[] annotations, 
        MediaType mediaType, 
        MultivaluedMap<String, Object> httpHeaders, 
        OutputStream entityStream) throws IOException, WebApplicationException { 
     mFile.streamFile(entityStream); //line 41 
    } 

} 

这里是MediaFile类减去getter和setter方法：

@Entity 
@XmlRootElement 
public class MediaFile { 
    @Id 
    @GeneratedValue 
    Long id; 

    @JsonIgnore 
    @ManyToOne(cascade=CascadeType.ALL) 
    @PrimaryKeyJoinColumn 
    MediaRepo repo; 

    String filePath; 
    String fileName; 

    transient JSch jsch; 
    transient Session session; 
    transient ChannelSftp sftp; 

    public MediaFile(){} 

    public void prepForDownload(){ 
     if(sftp != null) 
      return; 
     try{ 
      jsch = new JSch(); 
      session = jsch.getSession(repo.getUsername(), repo.getHost(), repo.getPort()); 
      session.setPassword(repo.getPassword()); 
      java.util.Properties config = new java.util.Properties(); 
      config.put("StrictHostKeyChecking", "no"); 
      session.setConfig(config); 
      session.connect(); 
      sftp = (ChannelSftp)session.openChannel("sftp"); 
     }catch(Exception e){ 
      e.printStackTrace(); 
     } 
    } 
    public long getFileSize(){ 
     prepForDownload(); 
     try { 
      return sftp.lstat(getCompletePath()).getSize(); 
     } catch (SftpException e) { 
      e.printStackTrace(); 
     } 
     return 0; 
    } 
    private String getCompletePath(){ 
     return repo.getBasePath()+filePath+fileName; 
    } 
    public void streamFile(OutputStream output){ 
     prepForDownload(); 
     try { 
      sftp.get(getCompletePath(), output); 
     } catch (SftpException e) { 
      e.printStackTrace(); 
     } 
    } 
} 

和这里的错误我收到：

13:50:05,260 ERROR [stderr] (default task-5) 4: 
13:50:05,260 ERROR [stderr] (default task-5) at com.jcraft.jsch.ChannelSftp.get(ChannelSftp.java:1011) 
13:50:05,260 ERROR [stderr] (default task-5) at com.jcraft.jsch.ChannelSftp.get(ChannelSftp.java:984) 
13:50:05,261 ERROR [stderr] (default task-5) at model.MediaFile.streamFile(MediaFile.java:75) 
13:50:05,261 ERROR [stderr] (default task-5) at MediaBodyWriter.writeTo(MediaBodyWriter.java:41) 
13:50:05,261 ERROR [stderr] (default task-5) at MediaBodyWriter.writeTo(MediaBodyWriter.java:1) 
13:50:05,261 ERROR [stderr] (default task-5) at MediaBodyWriter$Proxy$_$$_WeldClientProxy.writeTo(Unknown Source) 
13:50:05,261 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.writeTo(AbstractWriterInterceptorContext.java:131) 
13:50:05,261 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.interception.ServerWriterInterceptorContext.writeTo(ServerWriterInterceptorContext.java:60) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:120) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.security.doseta.DigitalSigningInterceptor.aroundWriteTo(DigitalSigningInterceptor.java:145) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:124) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.plugins.interceptors.encoding.GZIPEncodingInterceptor.aroundWriteTo(GZIPEncodingInterceptor.java:100) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.interception.AbstractWriterInterceptorContext.proceed(AbstractWriterInterceptorContext.java:124) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.ServerResponseWriter.writeNomapResponse(ServerResponseWriter.java:98) 
13:50:05,262 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.SynchronousDispatcher.writeResponse(SynchronousDispatcher.java:466) 
13:50:05,263 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:415) 
13:50:05,263 ERROR [stderr] (default task-5) at org.jboss.resteasy.core.SynchronousDispatcher.invoke(SynchronousDispatcher.java:202) 
13:50:05,263 ERROR [stderr] (default task-5) at org.jboss.resteasy.plugins.server.servlet.ServletContainerDispatcher.service(ServletContainerDispatcher.java:221) 
13:50:05,263 ERROR [stderr] (default task-5) at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:56) 
13:50:05,263 ERROR [stderr] (default task-5) at org.jboss.resteasy.plugins.server.servlet.HttpServletDispatcher.service(HttpServletDispatcher.java:51) 
13:50:05,263 ERROR [stderr] (default task-5) at javax.servlet.http.HttpServlet.service(HttpServlet.java:790) 
13:50:05,263 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletHandler.handleRequest(ServletHandler.java:85) 
13:50:05,263 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.security.ServletSecurityRoleHandler.handleRequest(ServletSecurityRoleHandler.java:62) 
13:50:05,264 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletDispatchingHandler.handleRequest(ServletDispatchingHandler.java:36) 
13:50:05,264 ERROR [stderr] (default task-5) at org.wildfly.extension.undertow.security.SecurityContextAssociationHandler.handleRequest(SecurityContextAssociationHandler.java:78) 
13:50:05,264 ERROR [stderr] (default task-5) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) 
13:50:05,264 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.security.SSLInformationAssociationHandler.handleRequest(SSLInformationAssociationHandler.java:131) 
13:50:05,264 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.security.ServletAuthenticationCallHandler.handleRequest(ServletAuthenticationCallHandler.java:57) 
13:50:05,264 ERROR [stderr] (default task-5) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) 
13:50:05,265 ERROR [stderr] (default task-5) at io.undertow.security.handlers.AbstractConfidentialityHandler.handleRequest(AbstractConfidentialityHandler.java:46) 
13:50:05,265 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.security.ServletConfidentialityConstraintHandler.handleRequest(ServletConfidentialityConstraintHandler.java:64) 
13:50:05,265 ERROR [stderr] (default task-5) at io.undertow.security.handlers.AuthenticationMechanismsHandler.handleRequest(AuthenticationMechanismsHandler.java:60) 
13:50:05,265 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.security.CachedAuthenticatedSessionHandler.handleRequest(CachedAuthenticatedSessionHandler.java:77) 
13:50:05,265 ERROR [stderr] (default task-5) at io.undertow.security.handlers.NotificationReceiverHandler.handleRequest(NotificationReceiverHandler.java:50) 
13:50:05,266 ERROR [stderr] (default task-5) at io.undertow.security.handlers.AbstractSecurityContextAssociationHandler.handleRequest(AbstractSecurityContextAssociationHandler.java:43) 
13:50:05,266 ERROR [stderr] (default task-5) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) 
13:50:05,266 ERROR [stderr] (default task-5) at org.wildfly.extension.undertow.security.jacc.JACCContextIdHandler.handleRequest(JACCContextIdHandler.java:61) 
13:50:05,266 ERROR [stderr] (default task-5) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) 
13:50:05,266 ERROR [stderr] (default task-5) at io.undertow.server.handlers.PredicateHandler.handleRequest(PredicateHandler.java:43) 
13:50:05,266 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletInitialHandler.handleFirstRequest(ServletInitialHandler.java:284) 
13:50:05,267 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletInitialHandler.dispatchRequest(ServletInitialHandler.java:263) 
13:50:05,267 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletInitialHandler.access$000(ServletInitialHandler.java:81) 
13:50:05,267 ERROR [stderr] (default task-5) at io.undertow.servlet.handlers.ServletInitialHandler$1.handleRequest(ServletInitialHandler.java:174) 
13:50:05,267 ERROR [stderr] (default task-5) at io.undertow.server.Connectors.executeRootHandler(Connectors.java:202) 
13:50:05,267 ERROR [stderr] (default task-5) at io.undertow.server.HttpServerExchange$1.run(HttpServerExchange.java:793) 
13:50:05,267 ERROR [stderr] (default task-5) at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142) 
13:50:05,268 ERROR [stderr] (default task-5) at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617) 
13:50:05,268 ERROR [stderr] (default task-5) at java.lang.Thread.run(Thread.java:745) 
13:50:05,268 ERROR [stderr] (default task-5) Caused by: java.lang.NullPointerException 
13:50:05,268 ERROR [stderr] (default task-5) at com.jcraft.jsch.ChannelSftp.get(ChannelSftp.java:994) 
13:50:05,269 ERROR [stderr] (default task-5) ... 47 more 

Answer 1

你必须致电上的，然后才能使用它，正如所有JSch SFTP示例所示。

例如，看到official JSch SFTP example：

Channel channel=session.openChannel("sftp"); 
channel.connect(); 
ChannelSftp c=(ChannelSftp)channel;