Java8 Optional多层嵌套循环取值避免空指针

偏执的太偏执、 2022-12-22 11:20 142阅读 0赞

/** * Optional避免空指针，采用默认值或者自定义抛出异常 * 使用场景：多层对象嵌套取值 * * **/
    public class OptionalTest { 
    
        @Test
        public void Test1() { 
            // 正常情况，都不为null,都可以正常执行
            User user = User.builder().address( Address.builder()
                    .country( Country.builder().countryName( "nj" )
                            .build() )
                    .build() )
                    .build();
    
            // user为null
            user = null;
    
            // Address 为null
            user = User.builder().address( null ).build();
    
            // country 为null
            user = User.builder().address( Address.builder()
                    .country( null ).build() ).build();
            
            OptTest( user );
    
        }
    
        public void OptTest(User user) { 
    
            // 第一种方式：存在空指针的风险，只要与一个对象为空就会空指针
            String countryName = user.getAddress().getCountry().getCountryName();
            System.out.println( "第一种方式：" + countryName );
    
            // 第二种方式：各种if判断避免了空指针，但是if层级太深，代码冗长
            if (user != null) { 
                Address address = user.getAddress();
                if (address != null) { 
                    Country country = address.getCountry();
                    if (country != null) { 
                        String couName = country.getCountryName();
                        System.out.println( "第二种方式：" + couName );
                    }
                }
            }
    
            // 第三种方式：代码简洁，避免空指针,武林那一步为空都会返回默认值
            String counName = Optional.ofNullable( user )
                    .map( User::getAddress )
                    .map( Address::getCountry )
                    .map( Country::getCountryName )
                    .orElse( "china" );
            System.out.println( "第三种方式：" + counName );
    
            // 第三种方式：代码简洁，避免空指针,武林那一步为空都会返回自定义异常
            String countryNameEx = Optional.ofNullable( user )
                    .map( User::getAddress )
                    .map( Address::getCountry )
                    .map( Country::getCountryName )
                    .orElseThrow( () -> new RuntimeException( "countryId is null" ) );
            System.out.println( "第四种方式：" + countryNameEx );
        }
    
    }

/** * @author zrj * @version V1.0 * @since 2020/11/20 **/
    @Data
    @Builder
    public class User { 
        private Integer userId;
    
        private String userName;
    
        private Address address;
    }
    
    @Data
    @Builder
    public class Address { 
        private Integer addressId;
    
        private String addressName;
    
        private Country country;
    }
    
    @Data
    @Builder
    public class Country { 
        private Integer countryId;
    
        private String countryName;
    }