我正在尝试使用sqoop将数据从mysql导入hdfs。为此，我使用以下命令。

sqoop import --connect jdbc:mysql://192.168.0.121:3306/snachitdb --username root --password root --table webdemo_vendorinfo --m 1 --target-dir /user/hduser/test/

我在jdbc url中的ip地址或主机名是正确的。
jdbc url中的端口号正确。
数据库服务器已启动。
数据库服务器正在接受tcp/ip连接。
但我仍然得到以下错误：我搜索了很多，但无法解决，请帮助我解决它。提前谢谢。

`15/03/05 14:44:48 ERROR manager.SqlManager: Error executing statement: com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.
com.mysql.jdbc.exceptions.jdbc4.CommunicationsException: Communications link failure

Last packet sent to the server was 0 ms ago.
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
    at com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1074)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2104)
    at com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:729)
    at com.mysql.jdbc.JDBC4Connection.<init>(JDBC4Connection.java:46)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:57)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:526)
    at com.mysql.jdbc.Util.handleNewInstance(Util.java:406)
    at com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:302)
    at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:283)
    at java.sql.DriverManager.getConnection(DriverManager.java:571)
    at java.sql.DriverManager.getConnection(DriverManager.java:215)
    at org.apache.sqoop.manager.SqlManager.makeConnection(SqlManager.java:877)
    at org.apache.sqoop.manager.GenericJdbcManager.getConnection(GenericJdbcManager.java:52)
    at org.apache.sqoop.manager.SqlManager.execute(SqlManager.java:736)
    at org.apache.sqoop.manager.SqlManager.execute(SqlManager.java:759)
    at org.apache.sqoop.manager.SqlManager.getColumnInfoForRawQuery(SqlManager.java:269)
    at org.apache.sqoop.manager.SqlManager.getColumnTypesForRawQuery(SqlManager.java:240)
    at org.apache.sqoop.manager.SqlManager.getColumnTypes(SqlManager.java:226)
    at org.apache.sqoop.manager.ConnManager.getColumnTypes(ConnManager.java:295)
    at org.apache.sqoop.orm.ClassWriter.getColumnTypes(ClassWriter.java:1829)
    at org.apache.sqoop.orm.ClassWriter.generate(ClassWriter.java:1641)
    at org.apache.sqoop.tool.CodeGenTool.generateORM(CodeGenTool.java:96)
    at org.apache.sqoop.tool.ImportTool.importTable(ImportTool.java:478)
    at org.apache.sqoop.tool.ImportTool.run(ImportTool.java:605)
    at org.apache.sqoop.Sqoop.run(Sqoop.java:143)
    at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
    at org.apache.sqoop.Sqoop.runSqoop(Sqoop.java:179)
    at org.apache.sqoop.Sqoop.runTool(Sqoop.java:218)
    at org.apache.sqoop.Sqoop.runTool(Sqoop.java:227)
    at org.apache.sqoop.Sqoop.main(Sqoop.java:236)
Caused by: java.net.ConnectException: Connection refused
    at java.net.PlainSocketImpl.socketConnect(Native Method)
    at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
    at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
    at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
    at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
    at java.net.Socket.connect(Socket.java:579)
    at java.net.Socket.connect(Socket.java:528)
    at java.net.Socket.<init>(Socket.java:425)
    at java.net.Socket.<init>(Socket.java:241)
    at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:256)
    at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:276)
    at com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2027)
    ... 30 more
15/03/05 14:44:48 ERROR tool.ImportTool: Encountered IOException running import job: java.io.IOException: No columns to generate for ClassWriter
    at org.apache.sqoop.orm.ClassWriter.generate(ClassWriter.java:1647)
    at org.apache.sqoop.tool.CodeGenTool.generateORM(CodeGenTool.java:96)
    at org.apache.sqoop.tool.ImportTool.importTable(ImportTool.java:478)
    at org.apache.sqoop.tool.ImportTool.run(ImportTool.java:605)
    at org.apache.sqoop.Sqoop.run(Sqoop.java:143)
    at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:70)
    at org.apache.sqoop.Sqoop.runSqoop(Sqoop.java:179)
    at org.apache.sqoop.Sqoop.runTool(Sqoop.java:218)
    at org.apache.sqoop.Sqoop.runTool(Sqoop.java:227)
    at org.apache.sqoop.Sqoop.main(Sqoop.java:236)