如何在用户定义的Java类中获取字段值？

问题描述：

我正试图从下面的转换中获得User Defined Java Class步骤中的Link字段。如何在用户定义的Java类中获取字段值？

这里是我写在User Defined Java Class代码：

private String link; 
public boolean processRow(StepMetaInterface smi, StepDataInterface sdi) throws KettleException 
{ 
    Object[] r=getRow(); 
    if (r == null) { 
     setOutputDone(); 
     return false; 
    } 

    if (first) { 
     link = getParameter("Link"); 
     first = false; 
    } 

    String linkField = get(Fields.In, link).getString(r); 
    logBasic("link:" + link); 


    return true; 

}

当我运行上面的代码，这里是我的定义的Java类的用户得到步骤错误：

2016/06/28 11:26:57 - User Defined Java Class.0 - ERROR (version 5.4.0.1-130, build 1 from 2015-06-14_12-34-55 by buildguy) : Unexpected error 
2016/06/28 11:26:57 - User Defined Java Class.0 - ERROR (version 5.4.0.1-130, build 1 from 2015-06-14_12-34-55 by buildguy) : org.pentaho.di.core.exception.KettleStepException: 
2016/06/28 11:26:57 - User Defined Java Class.0 - Unable to find In field helper for field name 'null' 
2016/06/28 11:26:57 - User Defined Java Class.0 - 
2016/06/28 11:26:57 - User Defined Java Class.0 - at org.pentaho.di.trans.steps.userdefinedjavaclass.TransformClassBase.get(TransformClassBase.java:628) 
2016/06/28 11:26:57 - User Defined Java Class.0 - at Processor.processRow(Processor.java:15) 
2016/06/28 11:26:57 - User Defined Java Class.0 - at org.pentaho.di.trans.steps.userdefinedjavaclass.UserDefinedJavaClass.processRow(UserDefinedJavaClass.java:1018) 
2016/06/28 11:26:57 - User Defined Java Class.0 - at org.pentaho.di.trans.step.RunThread.run(RunThread.java:62) 
2016/06/28 11:26:57 - User Defined Java Class.0 - at java.lang.Thread.run(Thread.java:745) 
2016/06/28 11:26:57 - User Defined Java Class.0 - Finished processing (I=0, O=0, R=1, W=0, U=0, E=1)

要确认字段，这里是预览数据的快照，直到Filter rows步骤：

我哪里错了？

答

我想通了我失踪的地方。在User Defined Java Class中，在下面的参数选项卡中，我需要明确定义字段名称和它的别名，例如：

如何在用户定义的Java类中获取字段值？

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