com.feilong.core.lang

Class ObjectUtil

java.lang.Object

com.feilong.core.lang.ObjectUtil

public final class ObjectUtil
extends Object

Object 工具类.

判断相等

1. ObjectUtils.equals(Object, Object) 支持两个值都是null的情况
2. Objects.equals(Object, Object) (since jdk1.7) 也支持两个值都是null的情况

Since:

1.0.0

Author:

feilong

See Also:

ObjectUtils, Objects

Method Summary

Methods

Modifier and Type	Method and Description
static <T> T	defaultIfNullOrEmpty(T object, T defaultValue) 如果 object 是null或者empty,返回默认值 defaultValue.
static boolean	isArray(Object object) 判断指定的对象 object是否是数组.
static boolean	isPrimitiveArray(Object object) 判断指定的对象 object 是否是原生类型数组.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

defaultIfNullOrEmpty

public static <T> T defaultIfNullOrEmpty(T object,
                         T defaultValue)

如果 object 是null或者empty,返回默认值 defaultValue.

示例:

 ObjectUtil.defaultIfNullOrEmpty(null, null)      = null
 ObjectUtil.defaultIfNullOrEmpty(null, "")        = ""
 ObjectUtil.defaultIfNullOrEmpty(null, "zz")      = "zz"
 ObjectUtil.defaultIfNullOrEmpty("abc", *)        = "abc"
 ObjectUtil.defaultIfNullOrEmpty(Boolean.TRUE, *) = Boolean.TRUE
 

说明:

1. 使用该方法,可以简化你的代码
2. 如果使用 import static 的特性,代码会更加简洁
3. 如果你只需要判断 null的场景,你可以使用 ObjectUtils.defaultIfNull(Object, Object)

对下面的代码重构:

 
 if (isNotNullOrEmpty(defaultReturnResult.getReturnObject())){
     return (String) defaultReturnResult.getReturnObject();
 }else{
     return "redirect:/";
 }
 
 

可以重构成:

 return ObjectUtil.defaultIfNullOrEmpty((String) defaultReturnResult.getReturnObject(), "redirect:/");
 

再比如:

 
 private void putItemToMap(Map<String, List<Item>> map,String categoryName,Item item){
     List<Item> itemList = map.get(categoryName);
 
     if (isNullOrEmpty(itemList)){
         itemList = new ArrayList<>();
     }
     itemList.add(item);
     map.put(categoryName, itemList);
 }
 
 

可以重构成:

 
 private void putItemToMap(Map<String, List<Item>> map,String categoryName,Item item){
     List<Item> itemList = ObjectUtil.defaultIfNullOrEmpty(map.get(categoryName), new ArrayList<Item>());
     itemList.add(item);
     map.put(categoryName, itemList);
 }
 

当然对于上面的case,你还可以直接调用 MapUtil.putMultiValue(java.util.Map, Object, Object)

Type Parameters:

T - the type of the object

Parameters:

object - the Object to test, 可以是 null or empty

defaultValue - the default value to return, 可以是 null or empty

Returns:

如果 object 是null或者empty,返回 defaultValue,否则返回 object

Since:

1.7.2

See Also:

ObjectUtils.defaultIfNull(Object, Object), ListUtils.defaultIfNull(java.util.List, java.util.List)

isArray

public static boolean isArray(Object object)

判断指定的对象 object是否是数组.

说明:

1. 支持判断原始类型数组 primitive 和包装类型数组

示例:

 int[] i = {};
 ObjectUtil.isArray(i);                       =true
 
 ObjectUtil.isArray(new int[] { 1, 2, 3 });   =true
 
 ObjectUtil.isArray(new Integer[0]);          =true
 ObjectUtil.isArray(new String[0]);           =true
 

instanceof和 Class.isArray()的区别:

通常使用instanceof操作符去判断一个对象 object 是否是数组 array.
在JVM层次,instanceof操作符 translates to a specific "instanceof" byte code, which is highly optimized in most JVM implementations.

而反射的方法(getClass().isArray()) is compiled to two separate "invokevirtual" instructions.
The more generic optimizations applied by the JVM to these may not be as fast as the hand-tuned optimizations inherent in the "instanceof" instruction.

有两种特殊情况: null references 和 primitive arrays.

	instanceof	getClass().isArray()
null reference	false	NullPointerException
原始类型数组primitive array	false	true

Parameters:

object - the object

Returns:

如果 object 是null,抛出 NullPointerException

Since:

1.3.0

See Also:

Java array reflection: isArray vs. instanceof, How to see if an object is an array without using reflection?

isPrimitiveArray

public static boolean isPrimitiveArray(Object object)

判断指定的对象 object 是否是原生类型数组.

示例:

 
 ObjectUtil.isPrimitiveArray(1)                           = false
 ObjectUtil.isPrimitiveArray(1L)                          = false
 ObjectUtil.isPrimitiveArray("1")                         = false
 
 
 ObjectUtil.isPrimitiveArray(new int[] {})                = true
 ObjectUtil.isPrimitiveArray(new int[] { 1, 2 })          = true
 ObjectUtil.isPrimitiveArray(new byte[] { 1, 2 })         = true
 
 ObjectUtil.isPrimitiveArray(new String[] { "1", "2" })   = false
 

Parameters:

object - the object

Returns:

如果 object 是null,抛出 NullPointerException

Since:

1.8.4