### Question:
MessageUtil extends AbstractCaller { @Description("Finds the value of the target field for a message within the list, matching the specified field.<br/>" + "<b>fieldName</b> - the field name for the matching group.<br/>" + "<b>fieldValue</b> - the field value for the matching group.<br/>" + "<b>targetFieldName</b> – the target field name." + "<b>return</b> - the target field value.<br/>" + "Considering the above said, the final syntax is:<br/>" + "#{FindField(groups, fieldName, fieldValue, targetFieldName)}") @UtilityMethod public Object FindField(List<IMessage> groups, String fieldName, Object fieldValue, String targetFieldName) { IMessage msg = FindGroup(groups, fieldName, fieldValue); targetFieldName = targetFieldName != null ? targetFieldName.trim() : null; return msg.isFieldSet(targetFieldName) ? msg.getField(targetFieldName) : null; }  @Description("Finds a message within the list, matching the specified field.<br/>" + "<b>fieldName</b> - the field name for the matching group.<br/>" + "<b>fieldValue</b> - the field value for the matching group.<br/>" + "<b>return</b> - a message matched by the field name and value.<br/>" + "Considering the above said, the final syntax is:<br/>" + "#{FindGroup(groups, fieldName, fieldValue)}") @UtilityMethod IMessage FindGroup(List<IMessage> groups, String fieldName, Object fieldValue); @Description("Finds the value of the target field for a message within the list, matching the specified field.<br/>" + "<b>fieldName</b> - the field name for the matching group.<br/>" + "<b>fieldValue</b> - the field value for the matching group.<br/>" + "<b>targetFieldName</b> – the target field name." + "<b>return</b> - the target field value.<br/>" + "Considering the above said, the final syntax is:<br/>" + "#{FindField(groups, fieldName, fieldValue, targetFieldName)}") @UtilityMethod Object FindField(List<IMessage> groups, String fieldName, Object fieldValue, String targetFieldName); @Description("Returns the special object representing any value.<br/>" + "This value can be used instead of '*' and referred to from other filters.<br/>" + "Example:<br/>" + "#{Any()} returns \"ANY\"") @UtilityMethod Object Any(); @Description("Returns the special object representing an empty value.<br/>" + "This value can be used instead of '#' and referred to from other filters.<br/>"+ "Example:<br/>" + "#{Empty()} returns \"EMPTY\"") @UtilityMethod Object Empty(); @Description("Returns the regex filter object for specified pattern.<br/>" + "Example: #{Regex(\".*\")}") @UtilityMethod IFilter Regex(String pattern);  }### Answer:
@Test public void testFindField() { try { messageUtil.FindField(null, null, null, null); Assert.fail("Null list"); } catch (EPSCommonException e) { e.printStackTrace(); } List<IMessage> list = new ArrayList<IMessage>(); try { messageUtil.FindField(list, null, null, null); Assert.fail("Null field name"); } catch (EPSCommonException e) { e.printStackTrace(); } String fieldName = "field"; try { messageUtil.FindField(list, fieldName, null, null); Assert.fail("Null target field name"); } catch (EPSCommonException e) { e.printStackTrace(); } String target = "target"; IMessage msg = new MapMessage("namespace", "name"); msg.addField("f1", "v1"); list.add(msg); Assert.assertEquals(null, messageUtil.FindField(list, fieldName, null, target)); Object value = 1; Object targetValue = "H2O"; msg = new MapMessage("namespace", "name"); msg.addField(fieldName, Integer.valueOf(1)); msg.addField(target, targetValue); list.add(msg); Assert.assertEquals(targetValue, messageUtil.FindField(list, fieldName, value, target)); }