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Java Reflection - Zugriff geschütztes Feld

Wie kann ich durch Reflektion auf ein geerbtes geschütztes Feld von einem Objekt aus zugreifen?

32
Moro

Zwei Probleme, mit denen Sie möglicherweise Probleme haben - das Feld ist möglicherweise nicht normal zugänglich (privat), und es ist nicht in der Klasse, die Sie betrachten, sondern irgendwo in der Hierarchie.

So etwas würde auch bei diesen Problemen funktionieren:

public class SomeExample {

  public static void main(String[] args) throws Exception{
    Object myObj = new SomeDerivedClass(1234);
    Class myClass = myObj.getClass();
    Field myField = getField(myClass, "value");
    myField.setAccessible(true); //required if field is not normally accessible
    System.out.println("value: " + myField.get(myObj));
  }

  private static Field getField(Class clazz, String fieldName)
        throws NoSuchFieldException {
    try {
      return clazz.getDeclaredField(fieldName);
    } catch (NoSuchFieldException e) {
      Class superClass = clazz.getSuperclass();
      if (superClass == null) {
        throw e;
      } else {
        return getField(superClass, fieldName);
      }
    }
  }
}

class SomeBaseClass {
  private Integer value;

  SomeBaseClass(Integer value) {
    this.value = value;
  }
}

class SomeDerivedClass extends SomeBaseClass {
  SomeDerivedClass(Integer value) {
    super(value);
  }
}
53
kenj0418

Verwenden Sie die Reflektion, um auf die Mitglieder der Klasseninstanz zuzugreifen, machen Sie sie zugänglich und legen Sie ihre jeweiligen Werte fest. Natürlich müssten Sie den Namen jedes Mitglieds wissen, das Sie ändern möchten, aber ich denke, das wird kein Problem sein.

public class ReflectionUtil {
    public static Field getField(Class clazz, String fieldName) throws NoSuchFieldException {
        try {
            return clazz.getDeclaredField(fieldName);
        } catch (NoSuchFieldException e) {
            Class superClass = clazz.getSuperclass();
            if (superClass == null) {
                throw e;
            } else {
                return getField(superClass, fieldName);
            }
        }
    }
    public static void makeAccessible(Field field) {
        if (!Modifier.isPublic(field.getModifiers()) ||
            !Modifier.isPublic(field.getDeclaringClass().getModifiers()))
        {
            field.setAccessible(true);
        }
    }
}

public class Application {
    public static void main(String[] args) throws Exception {
        KalaGameState obj = new KalaGameState();
        Field field = ReflectionUtil.getField(obj.getClass(), 'turn');
        ReflectionUtil.makeAccessible(field);
        field.setInt(obj, 666);
        System.out.println("turn is " + field.get(obj));
    }
}
6
jweyrich
field = myclass.getDeclaredField("myname");
field.setAccessible(true);
field.set(myinstance, newvalue);
4
Maurice Perry

Verwenden Sie FieldUtils.writeField(object, "fieldname", value, true) oder readField(object, "fieldname", true) aus Apache Commons lang3 .

4
mrts

Ich wollte nicht mehr Bibliotheken mitreißen, also habe ich eine reine Bibliothek erstellt, die für mich funktionierte. Es ist eine Erweiterung einer der Methoden von Jweyrich:

import Java.lang.reflect.Field;
import Java.lang.reflect.Modifier;
import Java.util.Date;
import Java.util.Random;
import Java.util.UUID;

public abstract class POJOFiller {

    static final Random random = new Random();

    public static void fillObject(Object ob) {
        Class<? extends Object> clazz = ob.getClass();

        do {
            Field[] fields = clazz.getDeclaredFields();
            fillForFields(ob, fields);

            if (clazz.getSuperclass() == null) {
                return;
            }
            clazz = clazz.getSuperclass();

        } while (true);

    }

    private static void fillForFields(Object ob, Field[] fields) {
        for (Field field : fields) {
            field.setAccessible(true);

            if(Modifier.isFinal(field.getModifiers())) {
                continue;
            }

            try {
                field.set(ob, generateRandomValue(field.getType()));
            } catch (IllegalArgumentException | IllegalAccessException e) {
                throw new IllegalStateException(e);
            }
        }
    }

    static Object generateRandomValue(Class<?> fieldType) {
        if (fieldType.equals(String.class)) {
            return UUID.randomUUID().toString();
        } else if (Date.class.isAssignableFrom(fieldType)) {
            return new Date(System.currentTimeMillis());
        } else if (Number.class.isAssignableFrom(fieldType)) {
            return random.nextInt(Byte.MAX_VALUE) + 1;
        } else if (fieldType.equals(Integer.TYPE)) {
            return random.nextInt();
        } else if (fieldType.equals(Long.TYPE)) {
            return random.nextInt();
        } else if (Enum.class.isAssignableFrom(fieldType)) {
            Object[] enumValues = fieldType.getEnumConstants();
            return enumValues[random.nextInt(enumValues.length)];
        } else if(fieldType.equals(Integer[].class)) {
            return new Integer[] {random.nextInt(), random.nextInt()};
        }
        else {
            throw new IllegalArgumentException("Cannot generate for " + fieldType);
        }
    }

}
1
Knubo

Если вы только получаете защищенное поле

Field protectedfield = Myclazz.class.getSuperclass().getDeclaredField("num");

Если вы используете EclipseCtrl+Spaceвызовет список методов при вводе "." после объекта

1
Ewebs

Wenn Sie Spring verwenden, bietet ReflectionTestUtils einige nützliche Tools, die hier mit minimalem Aufwand helfen.

Um beispielsweise einen geschützten Feldwert zu erhalten, der bekanntermaßen eine int ist:

int theIntValue = (int)ReflectionTestUtils.getField(theClass, "theProtectedIntField");

Oder alternativ, um den Wert dieses Feldes festzulegen:

ReflectionTestUtils.setField(theClass, "theProtectedIntField", theIntValue);
1
Steve Chambers

Eine generische Dienstprogrammmethode, um einen Getter in dieser oder einer übergeordneten Klasse auszuführen.

Angepasst an Marius ' Antwort.

public static Object RunGetter(String fieldname, Object o){
    Object result = null;
    boolean found = false;
    //Search this and all superclasses:
    for (Class<?> clas = o.getClass(); clas != null; clas = clas.getSuperclass()){
        if(found){
           break;
        }
        //Find the correct method:
        for (Method method : clas.getDeclaredMethods()){
            if(found){
                break;
            }
            //Method found:
            if ((method.getName().startsWith("get")) && (method.getName().length() == (fieldname.length() + 3))){ 
                if (method.getName().toLowerCase().endsWith(fieldname.toLowerCase())){                            
                    try{
                        result = method.invoke(o);  //Invoke Getter:
                        found = true;
                    } catch (IllegalAccessException | InvocationTargetException ex){
                        Logger.getLogger("").log(Level.SEVERE, "Could not determine method: " + method.getName(), ex);
                    }
                }
            }
        }
    }
    return result;
}

Hoffentlich ist das für jemanden nützlich.

0
pds

benutze dieses Dienstprogramm:

import Java.lang.reflect.*;
import Java.util.*;
import Java.util.stream.Stream;

import static Java.lang.String.format;

public final class ReflectionUtils {

    private ReflectionUtils() { }

    private static final String GETTER_PREFIX = "get";
    private static final String SETTER_PREFIX = "set";

    /**
     * Get name of getter
     *
     * @param fieldName fieldName
     * @return getter name
     */
    public static String getterByFieldName(String fieldName) {
        if (isStringNullOrEmpty(fieldName))
            return null;

        return convertFieldByAddingPrefix(fieldName, GETTER_PREFIX);
    }

    /**
     * Get name of setter
     *
     * @param fieldName fieldName
     * @return setter name
     */
    public static String setterByFieldName(String fieldName) {
        if (isStringNullOrEmpty(fieldName))
            return null;

        return convertFieldByAddingPrefix(fieldName, SETTER_PREFIX);
    }

    /**
     * Get the contents of the field with any access modifier
     *
     * @param obj obj
     * @param fieldName fieldName
     * @return content of field
     */
    public static Object getFieldContent(Object obj, String fieldName) {
        if (!isValidParams(obj, fieldName))
            return null;

        try {
            Field declaredField = getFieldAccessible(obj, fieldName);
            return declaredField.get(obj);
        } catch (IllegalAccessException e) {
            throw new IllegalArgumentException("Cannot get field content for field name: " + fieldName, e);
        }
    }

    /**
     * @param clazz clazz
     * @param fieldName fieldName
     * @return content static field
     */
    public static Object getStaticFieldContent(final Class<?> clazz, final String fieldName) {
        try {
            Field field = getFieldWithCheck(clazz, fieldName);
            field.setAccessible(true);
            return field.get(clazz);
        } catch (Exception e) {
            String exceptionMsg = format("Cannot find or get static field: '%s' from class: '%s'", fieldName, clazz);
            throw new RuntimeException(exceptionMsg, e);
        }
    }

    /**
     * Set the contents to the field with any access modifier
     *
     * @param obj obj
     * @param fieldName fieldName
     * @param value value
     */
    public static void setFieldContent(Object obj, String fieldName, Object value) {
        if (!isValidParams(obj, fieldName))
            return;

        try {
            Field declaredField = getFieldAccessible(obj, fieldName);
            declaredField.set(obj, value);
        } catch (IllegalAccessException e) {
            throw new IllegalArgumentException("Cannot set field content for field name: " + fieldName, e);
        }
    }

    /**
     * Call a method with any access modifier
     *
     * @param obj obj
     * @param methodName methodName
     * @return result of method
     */
    public static Object callMethod(Object obj, String methodName) {
        if (!isValidParams(obj, methodName))
            return null;

        try {
            Method method = obj.getClass().getMethod(methodName);
            method.setAccessible(true);
            return method.invoke(obj);
        } catch (NoSuchMethodException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e) {
            throw new IllegalArgumentException("Cannot invoke method name: " + methodName, e);
        }
    }

    /**
     * Get all fields even from parent
     *
     * @param clazz clazz
     * @return array of fields
     */
    public static Field[] getAllFields(Class<?> clazz) {
        if (clazz == null) return null;

        List<Field> fields = new ArrayList<>(Arrays.asList(clazz.getDeclaredFields()));
        if (clazz.getSuperclass() != null) {
            // danger! Recursion
            fields.addAll(Arrays.asList(getAllFields(clazz.getSuperclass())));
        }
        return fields.toArray(new Field[] {});
    }

    /**
     * Get the Field from Object even from parent
     *
     * @param obj obj
     * @param fieldName fieldName
     * @return {@code Optional}
     */
    public static Optional<Field> getField(Object obj, String fieldName) {
        if (!isValidParams(obj, fieldName))
            return Optional.empty();

        Class<?> clazz = obj.getClass();
        return getField(clazz, fieldName);
    }

    /**
     * Get the Field from Class even from parent
     *
     * @param clazz clazz
     * @param fieldName fieldName
     * @return {@code Optional}
     */
    public static Optional<Field> getField(Class<?> clazz, String fieldName) {
        if (!isValidParams(clazz, fieldName))
            return Optional.empty();

        Field[] fields = getAllFields(clazz);
        return Stream.of(fields)
                .filter(x -> x.getName().equals(fieldName))
                .findFirst();
    }

    /**
     * @param clazz clazz
     * @param fieldName fieldName
     * @return Class
     */
    public static Class<?> getFieldType(Class<?> clazz, String fieldName) {
        return getFieldWithCheck(clazz, fieldName).getType();
    }

    /**
     * @param clazz clazz
     * @param fieldName fieldName
     * @return Field
     */
    public static Field getFieldWithCheck(Class<?> clazz, String fieldName) {
        return ReflectionUtils.getField(clazz, fieldName)
                .orElseThrow(() -> {
                    String msg = String.format("Cannot find field name: '%s' from class: '%s'", fieldName, clazz);
                    return new IllegalArgumentException(msg);
                });
    }

    /**
     * Get the field values with the types already listed according to the field type
     *
     * @param clazz clazz
     * @param fieldName fieldName
     * @param fieldValue fieldValue
     * @return value cast to specific field type
     */
    public static Object castFieldValueByClass(Class<?> clazz, String fieldName, Object fieldValue) {
        Field field = getField(clazz, fieldName)
                .orElseThrow(() -> new IllegalArgumentException(String.format("Cannot find field by name: '%s'", fieldName)));

        Class<?> fieldType = field.getType();

        return castFieldValueByType(fieldType, fieldValue);
    }

    /**
     * @param fieldType fieldType
     * @param fieldValue fieldValue
     * @return casted value
     */
    public static Object castFieldValueByType(Class<?> fieldType, Object fieldValue) {
        if (fieldType.isAssignableFrom(Boolean.class)) {
            if (fieldValue instanceof String) {
                return convertStringToBoolean((String) fieldValue);
            }
            if (fieldValue instanceof Number) {
                return !(fieldValue).equals(0);
            }
            return fieldValue;
        }

        else if (fieldType.isAssignableFrom(Double.class)) {
            if (fieldValue instanceof String) {
                return Double.valueOf((String)fieldValue);
            }
            return ((Number) fieldValue).doubleValue();
        }

        else if (fieldType.isAssignableFrom(Long.class)) {
            if (fieldValue instanceof String) {
                return Long.valueOf((String)fieldValue);
            }
            return ((Number) fieldValue).longValue();
        }

        else if (fieldType.isAssignableFrom(Float.class)) {
            if (fieldValue instanceof String) {
                return Float.valueOf((String)fieldValue);
            }
            return ((Number) fieldValue).floatValue();
        }

        else if (fieldType.isAssignableFrom(Integer.class)) {
            if (fieldValue instanceof String) {
                return Integer.valueOf((String)fieldValue);
            }
            return ((Number) fieldValue).intValue();
        }

        else if (fieldType.isAssignableFrom(Short.class)) {
            if (fieldValue instanceof String) {
                return Short.valueOf((String)fieldValue);
            }
            return ((Number) fieldValue).shortValue();
        }

        return fieldValue;
    }

    private static boolean convertStringToBoolean(String s) {
        String trim = s.trim();
        return !trim.equals("") && !trim.equals("0") && !trim.toLowerCase().equals("false");
    }

    private static boolean isValidParams(Object obj, String param) {
        return (obj != null && !isStringNullOrEmpty(param));
    }

    private static boolean isStringNullOrEmpty(String fieldName) {
        return fieldName == null || fieldName.trim().length() == 0;
    }

    private static Field getFieldAccessible(Object obj, String fieldName) {
        Optional<Field> optionalField = getField(obj, fieldName);
        return optionalField
                .map(el -> {
                    el.setAccessible(true);
                    return el;
                })
                .orElseThrow(() -> new IllegalArgumentException("Cannot find field name: " + fieldName));
    }

    private static String convertFieldByAddingPrefix(String fieldName, String prefix) {
        return prefix + fieldName.substring(0, 1).toUpperCase() + fieldName.substring(1);
    }
}
0
FreeOnGoo

Meinen Sie vielleicht von einem anderen Objekt einen nicht vertrauenswürdigen Kontext mit einer SecurityManager-Menge? Das würde das Typsystem beschädigen, also kann man das nicht. In einem vertrauenswürdigen Kontext können Sie setAccessible aufrufen, um das Typsystem zu deaktivieren. Verwenden Sie im Idealfall keine Reflexion.

Sie könnten so etwas tun ...

Class clazz = Class.forName("SuperclassObject");

Field fields[] = clazz.getDeclaredFields();

for (Field field : fields) {
    if (field.getName().equals("fieldImLookingFor")) {
        field.set...() // ... should be the type, eg. setDouble(12.34);
    }
}

Möglicherweise müssen Sie auch die Erreichbarkeit ändern, wie in der Antwort von Maurice angegeben.

0
Craig Otis