Remove unsafe reflection trying to access the modifiers field (#1517)

Author: derklaro

src/main/java/com/comphenix/protocol/reflect/FieldUtils.java

@@ -395,20 +395,12 @@ public static void writeStaticField(Class cls, String fieldName, Object value,
 		writeStaticField(field, value);
 	}
 
+	/**
+	 * @deprecated Use {@link #writeStaticField(Class, String, Object, boolean)} instead.
+	 */
+	@Deprecated
 	public static void writeStaticFinalField(Class<?> clazz, String fieldName, Object value, boolean forceAccess) throws Exception {
-		Field field = getField(clazz, fieldName, forceAccess);
-		if (field == null) {
-			throw new IllegalArgumentException("Cannot locate field " + fieldName + " in " + clazz);
-		}
-
-		field.setAccessible(true);
-
-		Field modifiersField = Field.class.getDeclaredField("modifiers");
-		modifiersField.setAccessible(true);
-		modifiersField.setInt(field, field.getModifiers() & ~Modifier.FINAL);
-
-		field.setAccessible(true);
-		field.set(null, value);
+		writeStaticField(clazz, fieldName, value, forceAccess);
 	}
 
 	/**

src/main/java/com/comphenix/protocol/reflect/StructureModifier.java

@@ -308,7 +308,9 @@ public boolean isPublic(int fieldIndex) {
 	 * @param fieldIndex - index of the field.
 	 * @param value - TRUE if this field should be read only, FALSE otherwise.
 	 * @throws FieldAccessException If we cannot modify the read-only status.
+	 * @deprecated In recent java versions (starting at 9) the modifier field is secured and will not be writeable.
 	 */
+	@Deprecated
 	public void setReadOnly(int fieldIndex, boolean value) throws FieldAccessException {
 		if (fieldIndex < 0 || fieldIndex >= data.size())
 			throw new IllegalArgumentException("Index parameter is not within [0 - " + data.size() + ")");
@@ -325,7 +327,9 @@ public void setReadOnly(int fieldIndex, boolean value) throws FieldAccessExcepti
 	 * @param field - the field to change.
 	 * @param isReadOnly - TRUE if the field should be read only, FALSE otherwise.
 	 * @throws IllegalAccessException If an error occured.
+	 * @deprecated In recent java versions (starting at 9) the modifier field is secured and will not be writeable.
 	 */
+	@Deprecated
 	protected static void setFinalState(Field field, boolean isReadOnly) throws IllegalAccessException {
 	    if (isReadOnly)
 	    	FieldUtils.writeField((Object) field, "modifiers", field.getModifiers() | Modifier.FINAL, true);

src/main/java/com/comphenix/protocol/reflect/compiler/CompiledStructureModifier.java

@@ -58,8 +58,6 @@ public void setReadOnly(int fieldIndex, boolean value) throws FieldAccessExcepti
 				throw new IllegalStateException("Cannot make compiled field " + fieldIndex + " read only.");
 			}
 		}
-		
-		super.setReadOnly(fieldIndex, value);
 	}
 
 	// Speed up the default writer