JSch get（）因NullPointerException而失败
我有一个Jax-RS服务器，它应该保存一个可以通过ssh访问的文件列表，然后我可以通过HTTP下载或流式传输。
我一直在尝试用JSch的SFTP通道读取文件，但我一直收到NullPointerException 。
这是我写的MessageBodyWriter ：
@Provider @Produces("video/*") public class MediaBodyWriter implements MessageBodyWriter { @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 httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException { mFile.streamFile(entityStream); //line 41 } }
这是MediaFile类减去getter和setter：
@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(); } } }
这是我收到的错误：
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
您必须先调用ChannelSftp上的.connect() ，然后才能使用它，正如所有JSch SFTP示例所示。
例如，请参阅官方JSch SFTP示例 ：
Channel channel=session.openChannel("sftp"); channel.connect(); ChannelSftp c=(ChannelSftp)channel;