24个写出漂亮代码的小技巧

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class PersonRequest {

    @NotNull(message = "classId 不能为空")
    private String classId;

    @Size(max = 33)
    @NotNull(message = "name 不能为空")
    private String name;

    @Pattern(regexp = "(^Man$|^Woman$|^UGM$)", message = "sex 值不在可选范围")
    @NotNull(message = "sex 不能为空")
    private String sex;

    @Region
    private String region;

    @PhoneNumber(message = "phoneNumber 格式不正确")
    @NotNull(message = "phoneNumber 不能为空")
    private String phoneNumber;

}

@LogRecord(content = "修改了订单的配送地址：从“#oldAddress”, 修改到“#request.address”",
        bizNo="#request.deliveryOrderNo")
public void modifyAddress(updateDeliveryRequest request){
    // 查询出原来的地址是什么
    LogRecordContext.putVariable("oldAddress", DeliveryService.queryOldAddress(request.getDeliveryOrderNo()));
    // 更新派送信息 电话，收件人、地址
    doUpdate(request);
}

if (response.getData() != null && CollectionUtils.isNotEmpty(response.getData().getShoppingCartDTOList())) {
      cartList = response.getData().getShoppingCartDTOList().stream().map(CartResponseBuilderV2::buildCartList).collect(Collectors.toList());
}

T data = response.getData();
if (data != null && CollectionUtils.isNotEmpty(data.getShoppingCartDTOList())) {
  cartList = StreamUtil.map(data.getShoppingCartDTOList(), CartResponseBuilderV2::buildCartList);
}

public interface SmsSender {
    SmsResult send(String phone, String content);
    SmsResult sendWithTemplate(String phone, String templateId, String[] params);
}

/*
 * 阿里云短信服务
 */
public class AliyunSmsSender implements SmsSender {
  ...
}

/*
 * 腾讯云短信服务
 */
public class TencentSmsSender implements SmsSender {
  ...
}

public interface UserRepository extends JpaRepository<User, Long> {
  ...
}

@Repository
public class UserRedis {

    @Autowired
    private RedisTemplate<String, String> redisTemplate;

    public User save(User user) {
    }
}

// 取消订单消息生产者
public class CancelOrderProducer{
 ...
}
// 取消订单消息消费者
public class CancelOrderConsumer{
 ...
}

@RestController
public class UserController {
    @Autowired
    private UserRepository userRepository;

    @GetMapping("/users/{id}")
    public Result<UserVO> getUser(@RequestParam(name = "userId", required = true) Long userId) {
        User user = repository.findById(id)
                  .orElseThrow(() -> new UserNotFoundException(id));
        UserVO userVO = new UserVO();
        BeanUtils.copyProperties(user, userVO);//演示使用
        // 可能还有其他业务操作
        ...
        return Result.success(userVO);
    }
    ...
}

/**
 * 文件工具类
 */
public class FileUtil extends PathUtil {

    /**
     * 文件是否为空<br>
     * 目录：里面没有文件时为空 文件：文件大小为0时为空
     *
     * @param file 文件
     * @return 是否为空，当提供非目录时，返回false
     */
    public static boolean isEmpty(File file) {
        // 文件为空或者文件不存在直接返回 true
        if (null == file || false == file.exists()) {
            return true;
        }
        if (file.isDirectory()) {
            // 文件是文件夹的情况
            String[] subFiles = file.list();
            return ArrayUtil.isEmpty(subFiles);
        } else if (file.isFile()) {
            // 文件不是文件夹的情况
            return file.length() <= 0;
        }

        return false;
    }
}

public class IfElseDemo {

    public double calculateInsurance(double income) {
        if (income <= 10000) {
            return income*0.365;
        } else if (income <= 30000) {
            return (income-10000)*0.2+35600;
        } else if (income <= 60000) {
            return (income-30000)*0.1+76500;
        } else {
            return (income-60000)*0.02+105600;
        }

    }
}

public interface InsuranceCalculator {
    double calculate(double income);
}

public class FirstLevelCalculator implements InsuranceCalculator {
    public double calculate(double income) {
        return income * 0.365;
    }
}

public class SecondLevelCalculator implements InsuranceCalculator {
    public double calculate(double income) {
        return (income - 10000) * 0.2 + 35600;
    }
}

public class ThirdLevelCalculator implements InsuranceCalculator {
    public double calculate(double income) {
        return (income - 30000) * 0.1 + 76500;
    }
}

public class FourthLevelCalculator implements InsuranceCalculator {
    public double calculate(double income) {
        return (income - 60000) * 0.02 + 105600;
    }
}

import java.util.HashMap;
import java.util.Map;

public class InsuranceCalculatorFactory {
    private static final Map<String, InsuranceCalculator> CALCULATOR_MAP = new HashMap<>();

    static {
        CALCULATOR_MAP.put("first", new FirstLevelCalculator());
        CALCULATOR_MAP.put("second", new SecondLevelCalculator());
        CALCULATOR_MAP.put("third", new ThirdLevelCalculator());
        CALCULATOR_MAP.put("fourth", new FourthLevelCalculator());
    }

    public static InsuranceCalculator getCalculator(double income) {
        if (income <= 10000) {
            return CALCULATOR_MAP.get("first");
        } else if (income <= 30000) {
            return CALCULATOR_MAP.get("second");
        } else if (income <= 60000) {
            return CALCULATOR_MAP.get("third");
        } else {
            return CALCULATOR_MAP.get("fourth");
        }
    }
}

double income = 40000;
// 获取第三级保险费用计算器
InsuranceCalculator calculator = InsuranceCalculatorFactory.getCalculator(income);
double insurance = calculator.calculate(income);
System.out.println("保险费用为：" + insurance);

import java.util.HashMap;
import java.util.Map;
import java.util.function.Function;

public class InsuranceCalculatorFactory {
    private static final Map<String, Function<Double, Double>> CALCULATOR_MAP = new HashMap<>();

    static {
        CALCULATOR_MAP.put("first", income -> income * 0.365);
        CALCULATOR_MAP.put("second", income -> (income - 10000) * 0.2 + 35600);
        CALCULATOR_MAP.put("third", income -> (income - 30000) * 0.1 + 76500);
        CALCULATOR_MAP.put("fourth", income -> (income - 60000) * 0.02 + 105600);
    }

    public static Function<Double, Double> getCalculator(double income) {
        if (income <= 10000) {
            return CALCULATOR_MAP.get("first");
        } else if (income <= 30000) {
            return CALCULATOR_MAP.get("second");
        } else if (income <= 60000) {
            return CALCULATOR_MAP.get("third");
        } else {
            return CALCULATOR_MAP.get("fourth");
        }
    }
}

double income = 40000;
Function<Double, Double> calculator = InsuranceCalculatorFactory.getCalculator(income);
double insurance = calculator.apply(income);
System.out.println("保险费用为：" + insurance);;

Caffeine.newBuilder()
                // 设置最后一次写入或访问后经过固定时间过期
                .expireAfterWrite(60, TimeUnit.DAYS)
                // 初始的缓存空间大小
                .initialCapacity(100)
                // 缓存的最大条数
                .maximumSize(500)
                .build();

ChannelPipeline pipeline = ch.pipeline()
      // 添加一个用于对 HTTP 请求和响应报文进行编解码的 ChannelHandler
      .addLast(HTTP_CLIENT_CODEC, new HttpClientCodec())
       // 添加一个对 gzip 或者 deflate 格式的编码进行解码的 ChannelHandler
      .addLast(INFLATER_HANDLER, new HttpContentDecompressor())
       // 添加一个用于处理分块传输编码的 ChannelHandler
      .addLast(CHUNKED_WRITER_HANDLER, new ChunkedWriteHandler())
       // 添加一个处理 HTTP 请求并响应的 ChannelHandler
      .addLast(AHC_HTTP_HANDLER, new HttpHandler);

public class CompressionFilter implements Filter {
    // ...
    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // 检查是否支持压缩
        if (isCompressable(request, response)) {
            // 创建一个自定义的响应对象，用于在压缩数据时获取底层输出流
            CompressionServletResponseWrapper wrappedResponse = new CompressionServletResponseWrapper(
                    (HttpServletResponse) response);
            try {
                // 将请求转发给下一个过滤器或目标 Servlet/JSP 页面
                chain.doFilter(request, wrappedResponse);
                // 压缩数据并写入原始响应对象的输出流
                wrappedResponse.finishResponse();
            } catch (IOException e) {
                log.warn(sm.getString("compressionFilter.compressFailed"), e); //$NON-NLS-1$
                handleIOException(e, wrappedResponse);
            }
        } else {
            // 不支持压缩，直接将请求转发给下一个过滤器或目标 Servlet/JSP 页面
            chain.doFilter(request, response);
        }
    }
    // ...
}

public class CustomSpringEvent extends ApplicationEvent {
    private String message;

    public CustomSpringEvent(Object source, String message) {
        super(source);
        this.message = message;
    }
    public String getMessage() {
        return message;
    }
}

@Component
public class CustomSpringEventPublisher {
    @Autowired
    private ApplicationEventPublisher applicationEventPublisher;

    public void publishCustomEvent(final String message) {
        System.out.println("Publishing custom event. ");
        CustomSpringEvent customSpringEvent = new CustomSpringEvent(this, message);
        applicationEventPublisher.publishEvent(customSpringEvent);
    }
}

@Component
public class CustomSpringEventListener implements ApplicationListener<CustomSpringEvent> {
    @Override
    public void onApplicationEvent(CustomSpringEvent event) {
        System.out.println("Received spring custom event - " + event.getMessage());
    }
}

public abstract class AbstractDataImporter {
    private final String filePath;

    public AbstractDataImporter(String filePath) {
        this.filePath = filePath;
    }

    public void importData() throws IOException {
        List<String> data = readDataFromFile();
        validateData(data);
        saveDataToDatabase(data);
    }

    protected abstract List<String> readDataFromFile() throws IOException;

    protected void validateData(List<String> data) {
        // 若子类没有实现该方法，则不进行数据校验
    }

    protected abstract void saveDataToDatabase(List<String> data);

    protected String getFilePath() {
        return filePath;
    }
}

public class CsvDataImporter extends AbstractDataImporter {
    private final char delimiter;

    public CsvDataImporter(String filePath, char delimiter) {
        super(filePath);
        this.delimiter = delimiter;
    }

    @Override
    protected List<String> readDataFromFile() throws IOException {
        List<String> data = new ArrayList<>();
        try (BufferedReader reader = new BufferedReader(new FileReader(getFilePath()))) {
            String line;
            while ((line = reader.readLine()) != null) {
                data.add(line);
            }
        }
        return data;
    }

    @Override
    protected void validateData(List<String> data) {
        // 对 CSV 格式的数据进行校验，例如检查是否每行都有相同数量的字段等
    }

    @Override
    protected void saveDataToDatabase(List<String> data) {
        // 将 CSV 格式的数据保存到数据库中，例如将每行解析为一个对象，然后使用 JPA 保存到数据库中
    }
}

// 匿名内部类实现数组从小到大排序
Integer[] scores = {89, 100, 77, 90,  86};
Arrays.sort(scores,new Comparator<Integer>(){
    @Override
    public int compare(Integer o1, Integer o2) {
        return o1.compareTo(o2);
    }
});
for(Integer score:scores){
    System.out.print(score);
}
// 使用 Lambda 优化
Arrays.sort(scores,(o1,o2)->o1.compareTo(o2) );
// 还可以像下面这样写
Arrays.sort(scores,Comparator.comparing(Integer::intValue));

private Double calculateAverageGrade(Map<String, List<Integer>> gradesList, String studentName)
  throws Exception {
 return Optional.ofNullable(gradesList.get(studentName))// 创建一个Optional对象，传入参数为空时返回Optional.empty()
   .map(list -> list.stream().collect(Collectors.averagingDouble(x -> x)))// 对 Optional 的值进行操作
   .orElseThrow(() -> new NotFoundException("Student not found - " + studentName));// 当值为空时，抛出指定的异常
}

/**
 * 这个类具有两个特征
 * 1. 所有成员属性都是final
 * 2. 全部方法由构造方法，和两个成员属性访问器组成（共三个）
 * 那么这种类就很适合使用record来声明
 */
final class Rectangle implements Shape {
    final double length;
    final double width;

    public Rectangle(double length, double width) {
        this.length = length;
        this.width = width;
    }

    double length() { return length; }
    double width() { return width; }
}
/**
 * 1. 使用record声明的类会自动拥有上面类中的三个方法
 * 2. 在这基础上还附赠了equals()，hashCode()方法以及toString()方法
 * 3. toString方法中包括所有成员属性的字符串表示形式及其名称
 */
record Rectangle(float length, float width) { }

public class Employee {
    private int id;
    private String name;
    // getters and setters
}

public class EmployeeDTO {
    private int employeeId;
    private String employeeName;
    // getters and setters
}

@Mapper
public interface EmployeeMapper {
    // Spring 项目可以将 Mapper 注入到 IoC 容器中，这样就可以像 Spring Bean 一样调用了
    EmployeeMapper INSTANT = Mappers.getMapper(EmployeeMapper.class);

    @Mapping(target="employeeId", source="entity.id")
    @Mapping(target="employeeName", source="entity.name")
    EmployeeDTO employeeToEmployeeDTO(Employee entity);

    @Mapping(target="id", source="dto.employeeId")
    @Mapping(target="name", source="dto.employeeName")
    Employee employeeDTOtoEmployee(EmployeeDTO dto);
}

//  EmployeeDTO 转  Employee
Employee employee = EmployeeMapper.INSTANT.employeeToEmployeeDTO(employee);

//  Employee 转  EmployeeDTO
EmployeeDTO employeeDTO = EmployeeMapper.INSTANT.employeeDTOtoEmployee(employeeDTO);

try {
    //读文件操作
    readFile();
} catch (IOException e) {
    // 只保留了异常消息，栈没有记录
    log.error("文件读取错误, {}", e.getMessage());
}

try {
    //读文件操作
    readFile();
} catch (IOException e) {
    log.error("文件读取错误", e);
}

try {
  	 ...
} catch (IllegalArgumentException e) {
    log.error("出现异常啦", e);
    throw e;
}

try {
  	 ...
} catch (IllegalArgumentException e) {
    log.error("出现异常啦", e);
}
// 或者包装成自定义异常之后抛出
try {
  	 ...
} catch (IllegalArgumentException e) {
    throw new MyBusinessException("一段对异常的描述信息.", e);
}

@RestControllerAdvice
public class GlobalExceptionHandler {

    @ExceptionHandler(BusinessException.class)
    public Result businessExceptionHandler(HttpServletRequest request, BusinessException e){
        ...
        return Result.faild(e.getCode(), e.getMessage());
    }
    ...
}

//读取文本文件的内容
Scanner scanner = null;
try {
    scanner = new Scanner(new File("D://read.txt"));
    while (scanner.hasNext()) {
        System.out.println(scanner.nextLine());
    }
} catch (FileNotFoundException e) {
    e.printStackTrace();
} finally {
    if (scanner != null) {
        scanner.close();
    }
}

try (Scanner scanner = new Scanner(new File("test.txt"))) {
    while (scanner.hasNext()) {
        System.out.println(scanner.nextLine());
    }
} catch (FileNotFoundException fnfe) {
    fnfe.printStackTrace();
}

try (BufferedInputStream bin = new BufferedInputStream(new FileInputStream(new File("test.txt")));
     BufferedOutputStream bout = new BufferedOutputStream(new FileOutputStream(new File("out.txt")))) {
    int b;
    while ((b = bin.read()) != -1) {
        bout.write(b);
    }
}
catch (IOException e) {
    e.printStackTrace();
}

// 错误做法
public class Exceptions {
    public static BusinessException ORDEREXISTS = new BusinessException("订单已经存在", 3001);
...
}

// 错误做法
public UserDO getUser(Long userId) {
  return userService.getUser(userId);
}

public UserVo getUser(Long userId) {
  UserDO userDO = userService.getUser(userId)；
  UserVO userVO = new UserVO();
  BeanUtils.copyProperties(userDO, userVO);//演示使用
  return userVO;
}

public enum ResultEnum implements IResult {
    SUCCESS(2001, "接口调用成功"),
    VALIDATE_FAILED(2002, "参数校验失败"),
    COMMON_FAILED(2003, "接口调用失败"),
    FORBIDDEN(2004, "没有权限访问资源");

    private Integer code;
    private String message;
    ...
}

public class Result<T> {
    private Integer code;
    private String message;
    private T data;
    ...
    public static <T> Result<T> success(T data) {
        return new Result<>(ResultEnum.SUCCESS.getCode(), ResultEnum.SUCCESS.getMessage(), data);
    }

    public static Result<?> failed() {
        return new Result<>(ResultEnum.COMMON_FAILED.getCode(), ResultEnum.COMMON_FAILED.getMessage(), null);
    }
    ...
}

public class PostController {

	@GetMapping("/list")
	public R<List<SysPost>> getPosts() {
  ...
		return R.ok(posts);
	}
}