net.sf.extcos.util.ReflectionUtils Maven / Gradle / Ivy
package net.sf.extcos.util;
import static net.sf.extcos.util.Assert.iae;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;
import java.util.Arrays;
public class ReflectionUtils {
private ReflectionUtils() {
} // so it can't be instantiated
/**
* Get the field represented by the supplied {@link Field field object} on the
* specified {@link Object target object}. In accordance with {@link Field#get(Object)}
* semantics, the returned value is automatically wrapped if the underlying field
* has a primitive type.
* Thrown exceptions are handled via a call to {@link #handleReflectionException(Exception)}.
* @param field the field to get
* @param target the target object from which to get the field
* @return the field's current value
*/
public static Object getField(Field field, Object target) {
try {
return field.get(target);
}
catch (IllegalAccessException ex) {
handleReflectionException(ex);
throw new IllegalStateException(
"Unexpected reflection exception - " + ex.getClass().getName() + ": " + ex.getMessage());
}
}
/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied name. Searches all superclasses up to {@link Object}.
* @param clazz the class to introspect
* @param name the name of the field
* @return the corresponding Field object, or null if not found
*/
public static Field findField(Class clazz, String name) {
return findField(clazz, name, null);
}
/**
* Attempt to find a {@link Field field} on the supplied {@link Class} with the
* supplied name and/or {@link Class type}. Searches all superclasses
* up to {@link Object}.
* @param clazz the class to introspect
* @param name the name of the field (may be null if type is specified)
* @param type the type of the field (may be null if name is specified)
* @return the corresponding Field object, or null if not found
*/
public static Field findField(Class clazz, String name, Class type) {
Assert.notNull(clazz, iae(), "Class must not be null");
Assert.isTrue(name != null || type != null, iae(), "Either name or type of the field must be specified");
Class searchType = clazz;
while (!Object.class.equals(searchType) && searchType != null) {
Field[] fields = searchType.getDeclaredFields();
for (Field field : fields) {
if ((name == null || name.equals(field.getName())) && (type == null || type.equals(field.getType()))) {
return field;
}
}
searchType = searchType.getSuperclass();
}
return null;
}
/**
* Attempt to find a {@link Method} on the supplied class with the supplied name
* and parameter types. Searches all superclasses up to Object.
*
Returns null if no {@link Method} can be found.
* @param clazz the class to introspect
* @param name the name of the method
* @param paramTypes the parameter types of the method
* (may be null to indicate any signature)
* @return the Method object, or null if none found
*/
public static Method findMethod(Class clazz, String name, Class... paramTypes) {
Assert.notNull(clazz, iae(), "Class must not be null");
Assert.notNull(name, iae(), "Method name must not be null");
Class searchType = clazz;
while (searchType != null) {
Method[] methods = (searchType.isInterface() ? searchType.getMethods() : searchType.getDeclaredMethods());
for (Method method : methods) {
if (name.equals(method.getName())
&& (paramTypes == null || Arrays.equals(paramTypes, method.getParameterTypes()))) {
return method;
}
}
searchType = searchType.getSuperclass();
}
return null;
}
/**
* Invoke the specified {@link Method} against the supplied target object with no arguments.
* The target object can be null when invoking a static {@link Method}.
*
Thrown exceptions are handled via a call to {@link #handleReflectionException}.
* @param method the method to invoke
* @param target the target object to invoke the method on
* @return the invocation result, if any
* @see #invokeMethod(java.lang.reflect.Method, Object, Object[])
*/
public static Object invokeMethod(Method method, Object target) {
return invokeMethod(method, target, new Object[0]);
}
/**
* Invoke the specified {@link Method} against the supplied target object
* with the supplied arguments. The target object can be null
* when invoking a static {@link Method}.
*
* Thrown exceptions are handled via a call to
* {@link #handleReflectionException}.
*
* @param method
* the method to invoke
* @param target
* the target object to invoke the method on
* @param args
* the invocation arguments (may be null)
* @return the invocation result, if any
*/
public static Object invokeMethod(Method method, Object target,
Object[] args) {
try {
return method.invoke(target, args);
} catch (Exception ex) {
handleReflectionException(ex);
}
throw new IllegalStateException("Should never get here");
}
/**
* Handle the given reflection exception. Should only be called if no
* checked exception is expected to be thrown by the target method.
*
* Throws the underlying RuntimeException or Error in case of an
* InvocationTargetException with such a root cause. Throws an
* IllegalStateException with an appropriate message else.
*
* @param ex
* the reflection exception to handle
*/
public static void handleReflectionException(Exception ex) {
if (ex instanceof NoSuchMethodException) {
throw new IllegalStateException("Method not found: "
+ ex.getMessage());
}
if (ex instanceof IllegalAccessException) {
throw new IllegalStateException("Could not access method: "
+ ex.getMessage());
}
if (ex instanceof InvocationTargetException) {
handleInvocationTargetException((InvocationTargetException) ex);
}
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
handleUnexpectedException(ex);
}
/**
* Handle the given invocation target exception. Should only be called if no
* checked exception is expected to be thrown by the target method.
*
* Throws the underlying RuntimeException or Error in case of such a root
* cause. Throws an IllegalStateException else.
*
* @param ex
* the invocation target exception to handle
*/
public static void handleInvocationTargetException(
InvocationTargetException ex) {
rethrowRuntimeException(ex.getTargetException());
}
/**
* Rethrow the given {@link Throwable exception}, which is presumably the
* target exception of an {@link InvocationTargetException}. Should
* only be called if no checked exception is expected to be thrown by the
* target method.
*
* Rethrows the underlying exception cast to an {@link RuntimeException} or
* {@link Error} if appropriate; otherwise, throws an
* {@link IllegalStateException}.
*
* @param ex
* the exception to rethrow
* @throws RuntimeException
* the rethrown exception
*/
public static void rethrowRuntimeException(Throwable ex) {
if (ex instanceof RuntimeException) {
throw (RuntimeException) ex;
}
if (ex instanceof Error) {
throw (Error) ex;
}
handleUnexpectedException(ex);
}
/**
* Throws an IllegalStateException with the given exception as root cause.
*
* @param ex
* the unexpected exception
*/
private static void handleUnexpectedException(Throwable ex) {
// Needs to avoid the chained constructor for JDK 1.4 compatibility.
IllegalStateException isex = new IllegalStateException(
"Unexpected exception thrown");
isex.initCause(ex);
throw isex;
}
}