java - 设置私有(private)静态字段的值

Question

我想使用反射设置私有(private)字段的值以进行单元测试。

问题是，该字段是静态的。

这是我的工作内容:

/**
   * Use to set the value of a field you don't have access to, using reflection, for unit testing.
   * 
   * Returns true/false for success/failure.
   * 
   * @param p_instance an object to set a private field on
   * @param p_fieldName the name of the field to set
   * @param p_fieldValue the value to set the field to
   * @return true/false for success/failure
   */
  public static boolean setPrivateField(final Object p_instance, final String p_fieldName, final Object p_fieldValue) {
    if (null == p_instance)
      throw new NullPointerException("p_instance can't be null!");
    if (null == p_fieldName)
      throw new NullPointerException("p_fieldName can't be null!");

    boolean result = true;

    Class<?> klass = p_instance.getClass();

    Field field = null;
    try {
      field = klass.getDeclaredField(p_fieldName);

      field.setAccessible(true);
      field.set(p_instance, p_fieldValue);

    } catch (SecurityException e) {
      result = false;
    } catch (NoSuchFieldException e) {
      result = false;
    } catch (IllegalArgumentException e) {
      result = false;
    } catch (IllegalAccessException e) {
      result = false;
    }

    return result;
  }

我意识到这可能已经在 SO 上得到了回答，但我的搜索没有找到它......

Answer 1

基本上问题在于您的实用程序方法，它假设您有一个实例。设置私有(private)静态字段相当容易 - 它与实例字段的过程完全相同，除了您将 null 指定为实例。不幸的是，您的实用程序方法使用实例来获取类，并要求它不为空......

我会回应汤姆的警告:不要那样做。如果这是一个你可以控制的类，我会创建一个包级别的方法:

void setFooForTesting(Bar newValue)
{
    foo = newValue;
}

但是，如果您真的，真的想用反射设置它，这里有一个完整的示例:

import java.lang.reflect.*;

class FieldContainer
{
    private static String woot;

    public static void showWoot()
    {
        System.out.println(woot);
    }
}

public class Test
{
    // Declared to throw Exception just for the sake of brevity here
    public static void main(String[] args) throws Exception
    {
        Field field = FieldContainer.class.getDeclaredField("woot");
        field.setAccessible(true);
        field.set(null, "New value");
        FieldContainer.showWoot();
    }
}