How to specify in Java the value of the field for complex object in a compact way?

Question

we have the following problem with code. Our code must make lots of decision according to the fields of some object, and sometimes the fields are accessed through a complex path:

public void perform(OurBean bean) {
  if (bean != null 
    && bean.getWaybill() != null
    && bean.getWaybill().getTransaction() != null
    && bean.getWaybill().getTransaction().getGuid() != null) {
     // Do some action with the guid - a string
   }
}

What I would like to have is to do something like this:

public void perform(OurBean bean) {
  if (notEmpty(bean, "waybill.transaction.guid")) {
     // Do some action with the guid - a string
   }
}

Right now we have such a function implemented on our own, using a Reflection mechanism. Is there a better way to do it? JSP EL has exactly what we need - expressions using getter and setter methods. But how can I use that inside a Java code, not a JSP page, for some object? Could not find any good samples so far.

Wrap the `bean.getWaybill().getTransaction().getGuid()` in a try catch for `NullPointerException`, which you then ignore if it doesn't matter which object is null. — Sotirios Delimanolis, Jun 06 '13 at 17:19
No! Do not do that! Related/duplicate: http://stackoverflow.com/questions/271526/avoiding-null-statements-in-java — BalusC, Jun 06 '13 at 17:24
@BalusC Assuming the method doesn't care which object in the chain is null, what does it matter if we catch an NPE? We just don't `perform` if we can't find the last object. — Sotirios Delimanolis, Jun 06 '13 at 17:34
No, using exceptions like this is wrong. Besides, I asked mainly about the compact form "waybill.transaction.guid" - bean.getWaybill().getTransaction().getGuid() is a little bit overloaded with "noise". — SPIRiT_1984, Jun 06 '13 at 18:09
@BalusC this not a duplicate. I asked about using something like EL parser to make the code shorter, the question you relate to is about avoiding unnecessary if's. — SPIRiT_1984, Jun 06 '13 at 18:11
It's at least related. You've a design problem which is answered over there. So if you intend to fix the design problem, it's a duplicate. If you don't, then it's not, but you still have a design problem :) — BalusC, Jun 06 '13 at 18:12

score 0 · Answer 1 · answered Jun 06 '13 at 17:23

0

See the java.beans package

Example:

   if (notEmpty(new Expression(bean, "waybill.transaction.guid", null).getValue()) {
     // Do some action with the guid - a string
   }

This is just an example and it would probably need more love to make it work as you want, but you can reuse a lot of useful stuff from that package.

answered Jun 06 '13 at 17:23

Jiri Kremser

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According to the [javadoc for java.beans.Expression](http://docs.oracle.com/javase/7/docs/api/java/beans/Expression.html#Expression%28java.lang.Object,%20java.lang.String,%20java.lang.Object[]%29), that won't work. The String parameter is the name of a method in the bean's class, not a dot-expression. In fact I don't think the java.beans package has any classes that can do what EL does. – VGR Jun 06 '13 at 17:37
Right, javax.el is the right package to look into. Here is some tutorial for using EL outside the servlet container http://illegalargumentexception.blogspot.cz/2008/04/java-using-el-outside-j2ee.html – Jiri Kremser Jun 06 '13 at 21:46

score 0 · Accepted Answer · answered Jun 06 '13 at 17:46

0

If you have control over the bean classes, and if the bean classes are not auto-generated, add convenience methods to them:

public class ProgramLogic {
    public void perform(OurBean bean) {
        if (bean != null && bean.getWaybillTransactionId() != null) {
            // Do some action
        }
    }
}

public class OurBean {
    public String getWaybillTransactionId() {
        return waybill == null ? null : waybill.getTransactionGuid();
    }
}

public class Waybill {
    public String getTransactionGuid() {
        return transaction == null ? null : transaction.getGuid();
    }
}

answered Jun 06 '13 at 17:46

VGR

40,506
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That's a good thing, but this will just transfer the code from the procedure to the bean class, not making it any less. Besides, I was wondering more about how-to use EL parser inside Java for such a problem – SPIRiT_1984 Jun 06 '13 at 18:10
1

@SPIRiT_1984 The EL parser is most likely just doing what you were trying to do with reflection. – Sotirios Delimanolis Jun 06 '13 at 18:23

How to specify in Java the value of the field for complex object in a compact way?

2 Answers2