java 判断对象是否为空 博客分类： Java WebJava 对象是否为空过滤空行为空不为空StringUtil

java 中如何判断一个未知对象是否为空呢？

下面是一个通用的方法，判断字符串是否为空，集合是否为空，数组是否为空：

/**
	 * 判断对象或对象数组中每一个对象是否为空: 对象为null，字符序列长度为0，集合类、Map为empty
	 * 
	 * @param obj
	 * @return
	 */
	public static boolean isNullOrEmpty(Object obj) {
		if (obj == null)
			return true;

		if (obj instanceof CharSequence)
			return ((CharSequence) obj).length() == 0;

		if (obj instanceof Collection)
			return ((Collection) obj).isEmpty();

		if (obj instanceof Map)
			return ((Map) obj).isEmpty();

		if (obj instanceof Object[]) {
			Object[] object = (Object[]) obj;
			if (object.length == 0) {
				return true;
			}
			boolean empty = true;
			for (int i = 0; i < object.length; i++) {
				if (!isNullOrEmpty(object[i])) {
					empty = false;
					break;
				}
			}
			return empty;
		}
		return false;
	}

 参考：org.apache.commons.lang.StringUtils

 

应用场景：

读取excel文件，转化为一个二维数组：Object[][] arrays

但是excel中有空行，所以需要过滤Object[][] arrays中的空的一维数组：

/***
	 * 过滤数组中的空元素
	 * 
	 * 
	 * @param arrays
	 * @return
	 */
	public static Object[][] filterEmpty(Object[][] arrays) {
		int sumNotNull = 0;
		/***
		 * 统计非空元素的总个数
		 */
		for (int i = 0; i < arrays.length; i++) {
			Object object = arrays[i];
			if (!ValueWidget.isNullOrEmpty(object)
					&& !SystemUtil.isNullOrEmpty((Object[]) object)) {// 判断元素是否为空
				sumNotNull = sumNotNull + 1;
			}
		}
		Object[][] filtedObjs = new Object[sumNotNull][];
		int index = 0;
		for (int i = 0; i < arrays.length; i++) {
			Object[] object_tmp = arrays[i];
			if (!ValueWidget.isNullOrEmpty(object_tmp)
					&& !SystemUtil.isNullOrEmpty((Object[]) object_tmp)) {// 判断元素是否为空
				filtedObjs[index++] = object_tmp;
			}
		}
		return filtedObjs;
	}

 参阅附件中的方法com.common.util.SystemUtil.filterEmpty

 

判断对象的所有成员变量是否为空

/***
	 * Determine whether the object's fields are empty
	 * 
	 * @param obj
	 * @param isExcludeZero  :true:数值类型的值为0,则当做为空;----false:数值类型的值为0,则不为空
	 * 
	 * @return
	 * @throws SecurityException
	 * @throws IllegalArgumentException
	 * @throws NoSuchFieldException
	 * @throws IllegalAccessException
	 */
	public static boolean isNullObject(Object obj, boolean isExcludeZero)
			throws SecurityException, IllegalArgumentException,
			NoSuchFieldException, IllegalAccessException {
		if(ValueWidget.isNullOrEmpty(obj)){//对象本身就为null
			return true;
		}
		List<Field> fieldList = ReflectHWUtils.getAllFieldList(obj.getClass());
		boolean isNull = true;
		for (int i = 0; i < fieldList.size(); i++) {
			Field f = fieldList.get(i);
			Object propertyValue = null;
			try {
				propertyValue = getObjectValue(obj, f);
			} catch (NoSuchFieldException e) {
				e.printStackTrace();
			}

			if (!ValueWidget.isNullOrEmpty(propertyValue)) {// 字段不为空
				if (propertyValue instanceof Integer) {// 是数字
					if (!((Integer) propertyValue == 0 && isExcludeZero)) {
						isNull = false;
						break;
					}
				} else if (propertyValue instanceof Double) {// 是数字
					if (!((Double) propertyValue == 0 && isExcludeZero)) {
						isNull = false;
						break;
					}
				}else if (propertyValue instanceof Float) {// 是数字
					if (!((Float) propertyValue == 0 && isExcludeZero)) {
						isNull = false;
						break;
					}
				}else if (propertyValue instanceof Short) {// 是数字
					if (!((Short) propertyValue == 0 && isExcludeZero)) {
						isNull = false;
						break;
					}
				}else {
					isNull = false;
					break;
				}
			}
		}
		return isNull;
	}

 测试:

@Test
	public void test_isNullObject() throws SecurityException,
			IllegalArgumentException, NoSuchFieldException,
			IllegalAccessException {
		Person2 p = new Person2();
		Assert.assertEquals(true, ReflectHWUtils.isNullObject(p, true));
		Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));

		p.setAddress("beijing");
		Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, true));
		Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));

		p.setAddress(null);
		p.setId(0);
		Assert.assertEquals(true, ReflectHWUtils.isNullObject(p, true));
		Assert.assertEquals(false, ReflectHWUtils.isNullObject(p, false));

	}

 Person2 源代码(省略getter,setter方法):

import java.sql.Timestamp;

public class Person2 {
	private int id;
	private int age;
	private double weight;
	private String personName;
	private Timestamp birthdate;
	public String identitify;
	protected String address;
	String phone;
	
}