问题
I've got a Jax-RS server which is supposed to keep a list of files accessible via ssh that I can then download or stream via HTTP.
I've been trying to read the files with JSch's SFTP channel, but I keep receiving a NullPointerException.
Here's the MessageBodyWriter I wrote:
@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
}
}
Here's MediaFile class minus the getters and setters:
@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();
}
}
}
And here's the error I'm receiving:
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
回答1:
You have to call the .connect() on the ChannelSftp, before you can use it, as all JSch SFTP examples show.
For example, see the official JSch SFTP example:
Channel channel=session.openChannel("sftp");
channel.connect();
ChannelSftp c=(ChannelSftp)channel;
来源：https://stackoverflow.com/questions/37799006/jsch-get-fails-with-nullpointerexception