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
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2024-02-24 20:03:16
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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; }
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