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 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;

}