Java, reflection convert field into JAXBElement - soap

Question

I am trying to perform logging of SOAPMessage.
This object contains both wrapper classes and JAXBElements, I am doing something like this
#Before("soapRequest()")
public void logBefore(JoinPoint joinPoint) {
Object[] signatureArgs = joinPoint.getArgs();
System.out.println("\n\n\n");
for (Object signatureArg : signatureArgs) {
StringBuilder sb = new StringBuilder();
try {
Field[] aClassFields = signatureArg.getClass().getDeclaredFields();
sb.append(signatureArg.getClass().getSimpleName() + " [ ");
for (Field f : aClassFields) {
f.setAccessible(true);
String fName = f.getName();
String value = "";
if(f.get(signatureArg) instanceof JAXBElement) {
log.info("is instance of");
JAXBElement val = (JAXBElement) f.get(signatureArg);
log.info(val.toString());
value = val.getValue().toString();
} else {
value = f.get(signatureArg).toString();
}
sb.append("(" + f.getType() + ") " + fName + " = " + value + ", ");
}
sb.append("]");
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(sb.toString());
}
}
However this line throws NPE:
if(f.get(signatureArg) instanceof JAXBElement) {
log.info("is instance of");
JAXBElement val = (JAXBElement) f.get(signatureArg);
log.info(val.toString());
value = val.getValue().toString();
}
How Can I check if the field is instance of JAXBElement and extract value from it?

Answer 1

Actually I think your NPE occurs in the then block at this line of code:
value = f.get(signatureArg).toString();
It happens if the field value is null because on null you cannot call toString(). By the way, this should happen for any null field, not just for JAXBElement. You do not need toString(), you can just remove it because when you print any object, it will automatically use its toString() representation where applicable.
In my opinion your code is also more complicated than necessary and with some restructuring and renaming variables the then block is no longer necessary at all. Here is my MCVE in plain Java + AspectJ (no Spring) for you:
package de.scrum_master.app;
import javax.xml.bind.JAXBElement;
public class Container {
private String name;
private JAXBElement jaxbElement;
public Container(String name, JAXBElement jaxbElement) {
this.name = name;
this.jaxbElement = jaxbElement;
}
}
package de.scrum_master.app;
import javax.xml.bind.JAXBElement;
import javax.xml.namespace.QName;
public class Application {
public void doSomething(int number, String text, Container myContainer) {}
public static void main(String[] args) {
Application application = new Application();
application.doSomething(11, "foo", new Container("bar", new JAXBElement(new QName("local"), String.class, "dummy")));
application.doSomething(11, "foo", new Container("bar", null));
}
}
package de.scrum_master.aspect;
import java.lang.reflect.Field;
import javax.xml.bind.JAXBElement;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
#Aspect
public class MyAspect {
#Pointcut("execution(* doSomething(..))")
private void soapRequest() {}
#Before("soapRequest()")
public void logBefore(JoinPoint joinPoint) {
System.out.println(joinPoint);
for (Object methodArg : joinPoint.getArgs()) {
StringBuilder sb = new StringBuilder();
try {
sb.append(methodArg.getClass().getSimpleName() + " [ ");
for (Field field : methodArg.getClass().getDeclaredFields()) {
field.setAccessible(true);
String fieldName = field.getName();
Object value = field.get(methodArg);
if (value instanceof JAXBElement) {
System.out.println(" -> is instance of");
JAXBElement jaxbElement = (JAXBElement) value;
System.out.println(" -> " + jaxbElement);
value = jaxbElement.getValue();
}
// Un-comment this in order to see the NPE
//else {
// value = field.get(methodArg).toString();
//}
sb.append("(" + field.getType() + ") " + fieldName + " = " + value + ", ");
}
sb.append("]");
} catch (Exception e) {
e.printStackTrace();
}
System.out.println(" " + sb);
}
}
}
The console log looks like this:
execution(void de.scrum_master.app.Application.doSomething(int, String, Container))
Integer [ (int) MIN_VALUE = -2147483648, (int) MAX_VALUE = 2147483647, (class java.lang.Class) TYPE = int, (class [C) digits = [C#8efb846, (class [C) DigitTens = [C#2a84aee7, (class [C) DigitOnes = [C#a09ee92, (class [I) sizeTable = [I#30f39991, (int) value = 11, (int) SIZE = 32, (int) BYTES = 4, (long) serialVersionUID = 1360826667806852920, ]
String [ (class [C) value = [C#4a574795, (int) hash = 0, (long) serialVersionUID = -6849794470754667710, (class [Ljava.io.ObjectStreamField;) serialPersistentFields = [Ljava.io.ObjectStreamField;#f6f4d33, (interface java.util.Comparator) CASE_INSENSITIVE_ORDER = java.lang.String$CaseInsensitiveComparator#23fc625e, ]
-> is instance of
-> javax.xml.bind.JAXBElement#4f023edb
Container [ (class java.lang.String) name = bar, (class javax.xml.bind.JAXBElement) jaxbElement = dummy, ]
execution(void de.scrum_master.app.Application.doSomething(int, String, Container))
Integer [ (int) MIN_VALUE = -2147483648, (int) MAX_VALUE = 2147483647, (class java.lang.Class) TYPE = int, (class [C) digits = [C#8efb846, (class [C) DigitTens = [C#2a84aee7, (class [C) DigitOnes = [C#a09ee92, (class [I) sizeTable = [I#30f39991, (int) value = 11, (int) SIZE = 32, (int) BYTES = 4, (long) serialVersionUID = 1360826667806852920, ]
String [ (class [C) value = [C#4a574795, (int) hash = 0, (long) serialVersionUID = -6849794470754667710, (class [Ljava.io.ObjectStreamField;) serialPersistentFields = [Ljava.io.ObjectStreamField;#f6f4d33, (interface java.util.Comparator) CASE_INSENSITIVE_ORDER = java.lang.String$CaseInsensitiveComparator#23fc625e, ]
Container [ (class java.lang.String) name = bar, (class javax.xml.bind.JAXBElement) jaxbElement = null, ]
See? Your error has gone. Un-comment the else block in order to see it re-appear, then remove the .toString() from the line and it goes away again. Maybe it helps you understand your error better.
By the way, I think the log output looks kinda ugly. Did you also notice that you print static fields too? You should probably filter them out. But I did not want to change more of your code because I still want you to recognise it.
The short version of your aspect without the additional debug logging for JAXBElement and without try - catch but a declared exception instead would be:
package de.scrum_master.aspect;
import java.lang.reflect.Field;
import javax.xml.bind.JAXBElement;
import org.aspectj.lang.JoinPoint;
import org.aspectj.lang.annotation.Aspect;
import org.aspectj.lang.annotation.Before;
import org.aspectj.lang.annotation.Pointcut;
#Aspect
public class MyAspect {
#Pointcut("execution(* doSomething(..))")
private void soapRequest() {}
#Before("soapRequest()")
public void logBefore(JoinPoint joinPoint) throws Throwable {
System.out.println(joinPoint);
for (Object methodArg : joinPoint.getArgs()) {
StringBuilder sb = new StringBuilder();
sb.append(methodArg.getClass().getSimpleName() + " [ ");
for (Field field : methodArg.getClass().getDeclaredFields()) {
field.setAccessible(true);
String fieldName = field.getName();
Object value = field.get(methodArg);
if (value instanceof JAXBElement)
value = ((JAXBElement) value).getValue();
sb.append("(" + field.getType() + ") " + fieldName + " = " + value + ", ");
}
sb.append("]");
System.out.println(" " + sb);
}
}
}