optional处理空值

一时失言乱红尘 2022-05-20 10:25 274阅读 0赞

import java.util.Optional;
    
    import org.junit.Test;
    
    /*
     * 一、Optional 容器类：用于尽量避免空指针异常
     * 	Optional.of(T t) : 创建一个 Optinal 实例
     * 	Optional.empty() : 创建一个空的 Optional 实例
     * 	Optional.ofNullable(T t):若 t 不为 null,创建 Optional 实例,否则创建空实例
     * 	isPresent() : 判断是否包含值
     * 	orElse(T t) :  如果调用对象包含值，返回该值，否则返回t
     * 	orElseGet(Supplier s) :如果调用对象包含值，返回该值，否则返回 s 获取的值
     * 	map(Function f): 如果有值对其处理，并返回处理后的Optional，否则返回 Optional.empty()
     * 	flatMap(Function mapper):与 map 类似，要求返回值必须是Optional
     */
    public class TestOptional {
    	
    	@Test
    	public void test4(){
    		Optional<Employee> op = Optional.of(new Employee(101, "张三", 18, 9999.99));
    		
    		Optional<String> op2 = op.map(Employee::getName);
    		System.out.println(op2.get());
    		
    		Optional<String> op3 = op.flatMap((e) -> Optional.of(e.getName()));
    		System.out.println(op3.get());
    	}
    	
    	@Test
    	public void test3(){
    		Optional<Employee> op = Optional.ofNullable(new Employee());
    		
    		if(op.isPresent()){
    			System.out.println(op.get());
    		}
    		
    		Employee emp = op.orElse(new Employee("张三"));
    		System.out.println(emp);
    		
    		Employee emp2 = op.orElseGet(() -> new Employee());
    		System.out.println(emp2);
    	}
    	
    	@Test
    	public void test2(){
    		/*Optional<Employee> op = Optional.ofNullable(null);
    		System.out.println(op.get());*/
    		
    //		Optional<Employee> op = Optional.empty();
    //		System.out.println(op.get());
    	}
    
    	@Test
    	public void test1(){
    		Optional<Employee> op = Optional.of(new Employee());
    		Employee emp = op.get();
    		System.out.println(emp);
    	}
    	
    	@Test
    	public void test5(){
    		Man man = new Man();
    		
    		String name = getGodnessName(man);
    		System.out.println(name);
    	}
    	
    
    	public String getGodnessName(Man man){
    		if(man != null){
    			Godness g = man.getGod();
    			
    			if(g != null){
    				return g.getName();
    			}
    		}
    		
    		return "";
    	}
    	
    	//运用 Optional 的实体类
    	@Test
    	public void test6(){
    		Optional<Godness> godness = Optional.ofNullable(new Godness("林志玲"));
    		
    		Optional<NewMan> op = Optional.ofNullable(new NewMan(godness));
    		String name = getGodnessName2(op);
    		System.out.println(name);
    	}
    	
    	public String getGodnessName2(Optional<NewMan> man){
    		return man.orElse(new NewMan())
    				  .getGodness()
    				  .orElse(new Godness("VV"))
    				  .getName();
    	}
    }

Optional<List<String>> supplierSnList = Optional.ofNullable(barCodeVO.getSupplierSnList());
    //       //主要用来处理前端没有传supplierSnList字段的情况，不传也不会报错
    //       if(supplierSnList.isPresent()&&(!supplierSnList.get().isEmpty())) .
             if(barCodeVO.getSupplierSnList()!=null&&barCodeVO.getSupplierSnList().size()>0){

List<String> tempAssetSNList = context.getAssetSNAddVOList().stream().map(AssetSNAddVO::getSnCode).collect(Collectors.toList());