java 8 optional

例子：

类：

    public class User {
                private String name;
                public String getName() {
                    return name;
                }
                public void setName(String name) {
                    this.name = name;
                }
          }

一、之前对空的判定

            @Test
            public void testOpt() {
                User u = new User();
                u.setName("hy");
                if (u != null && u.getName() != null) {
                    System.out.println(u.getName());
                }
            }

二、使用optional对空的判定

      @Test(expected = MyException.class)
      public void testOpt() {
            User s = new User();
             s = null;
              Optional<User> opt = Optional.ofNullable(s);
              String name = opt.map(user -> user.getName()).orElseThrow(()-> new MyException("异常"));
                //Assert.assertEquals("hy", name);
                System.out.println(name);
          }

自定义异常：

          public class MyException extends RuntimeException {
                 MyException() {
               }
                MyException(String mgs) {
                    super(mgs);
                }
            }