问题原因：数据库的IP/用户名/密码/数据库名称 错误导致连接不上
ERROR tool.ImportTool: Import failed: java.io.IOException: No columns to generate for ClassWriter
at org.apache.sqoop.orm.ClassWriter.generate(ClassWriter.java:1677)
at org.apache.sqoop.tool.CodeGenTool.generateORM(CodeGenTool.java:106)
at org.apache.sqoop.tool.ImportTool.importTable(ImportTool.java:501)
at org.apache.sqoop.tool.ImportTool.run(ImportTool.java:628)
at org.apache.sqoop.tool.JobTool.execJob(JobTool.java:243)
at org.apache.sqoop.tool.JobTool.run(JobTool.java:298)
at org.apache.sqoop.Sqoop.run(Sqoop.java:147)
at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
at org.apache.sqoop.Sqoop.runSqoop(Sqoop.java:183)
at org.apache.sqoop.Sqoop.runTool(Sqoop.java:234)
at org.apache.sqoop.Sqoop.runTool(Sqoop.java:243)
at org.apach