END
开发者技术前线 ，汇集技术前线快讯和关注行业趋势，大厂干货，是开发者经历和成长的优秀指南。
深入理解 Java 多线程核心技术
2020 年九大顶级 Java 框架如何教女朋友学 Python？
Python 2.7 ：今天起正式停用
其他
细思极恐，你真的会写java吗
点击“开发者技术前线”，选择“星标🔝”
13：21 在看|星标|留言, 真爱
导语
自2013年毕业后，今年已经是我工作的第4个年头了，总在做java相关的工作，终于有时间坐下来，写一篇关于java写法的一篇文章，来探讨一下如果你真的是一个java程序员，那你真的会写java吗? 笔者是一个务实的程序员，故本文绝非扯淡文章，文中内容都是干货，望读者看后，能有所收获。
讲述方向
技术点
开发工具
更换IDE
别告诉我快捷键不好用
bean
domain包名
com.xxx.domain ，这样写好像已经成为了行业的一种约束，数据库映射对象就应该是domain。但是你错了，domain 是一个领域对象，往往我们再做传统java软件web开发中，这些domain都是贫血模型，是没有行为的，或是没有足够的领域模型的行为的，所以，以这个理论来讲，这些domain都应该是一个普通的entity对象，并非领域对象，所以请把包名改为:com.xxx.entity。DTO
DTO转化
场景
@RestController
public class UserApi {
@Autowired
private UserService userService;
@PostMapping
public User addUser(UserInputDTO userInputDTO){
User user = new User();
user.setUsername(userInputDTO.getUsername());
user.setAge(userInputDTO.getAge());
return userService.addUser(user);
}
}
user.setUsername(userInputDTO.getUsername());
user.setAge(userInputDTO.getAge());
请使用工具
org.springframework.beans.BeanUtils#copyProperties对代码进行重构和优化:public User addUser(UserInputDTO userInputDTO){
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return userService.addUser(user);
}
转化的语义
BeanUtils.copyProperties(userInputDTO,user);
public User addUser(UserInputDTO userInputDTO){
User user = convertFor(userInputDTO);
return userService.addUser(user);
}
private User convertFor(UserInputDTO userInputDTO){
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return user;
}
return userService.addUser(user);
抽象接口定义
T convert(S s);
}
@Override
public User convert(UserInputDTO userInputDTO) {
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return user;
}
}
@RestController
public class UserApi {
@Autowired
private UserService userService;
@PostMapping
public User addUser(UserInputDTO userInputDTO){
User user = new UserInputDTOConvert().convert(userInputDTO);
return userService.addUser(user);
}
}
review code
UserOutputDTO:public UserOutputDTO addUser(UserInputDTO userInputDTO){
User user = new UserInputDTOConvert().convert(userInputDTO);
User saveUserResult = userService.addUser(user);
UserOutputDTO result = new UserOutDTOConvert().convertToUser(saveUserResult);
return result;
}
private String username;
private int age;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public User convertToUser(){
UserInputDTOConvert userInputDTOConvert = new UserInputDTOConvert();
User convert = userInputDTOConvert.convert(this);
return convert;
}
private static class UserInputDTOConvert implements DTOConvert<UserInputDTO,User> {
@Override
public User convert(UserInputDTO userInputDTO) {
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return user;
}
}
}
User saveUserResult = userService.addUser(user);
User saveUserResult = userService.addUser(user);
再查工具类
DTOConvert接口，但是这样真的就没有问题，不需要再思考了吗？我觉得并不是，对于Convert这种转化语义来讲，很多工具类中都有这样的定义，这中Convert并不是业务级别上的接口定义，它只是用于普通bean之间转化属性值的普通意义上的接口定义，所以我们应该更多的去读其他含有Convert转化语义的代码。我仔细阅读了一下GUAVA的源码，发现了com.google.common.base.Convert这样的定义:protected abstract B doForward(A a);
protected abstract A doBackward(B b);
//其他略
}
@Override
public User convert(UserInputDTO userInputDTO) {
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return user;
}
}
@Override
protected User doForward(UserInputDTO userInputDTO) {
User user = new User();
BeanUtils.copyProperties(userInputDTO,user);
return user;
}
@Override
protected UserInputDTO doBackward(User user) {
UserInputDTO userInputDTO = new UserInputDTO();
BeanUtils.copyProperties(user,userInputDTO);
return userInputDTO;
}
}
private String username;
private int age;
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public User convertToUser(){
UserDTOConvert userDTOConvert = new UserDTOConvert();
User convert = userDTOConvert.convert(this);
return convert;
}
public UserDTO convertFor(User user){
UserDTOConvert userDTOConvert = new UserDTOConvert();
UserDTO convert = userDTOConvert.reverse().convert(user);
return convert;
}
private static class UserDTOConvert extends Converter<UserDTO, User> {
@Override
protected User doForward(UserDTO userDTO) {
User user = new User();
BeanUtils.copyProperties(userDTO,user);
return user;
}
@Override
protected UserDTO doBackward(User user) {
UserDTO userDTO = new UserDTO();
BeanUtils.copyProperties(user,userDTO);
return userDTO;
}
}
}
public UserDTO addUser(UserDTO userDTO){
User user = userDTO.convertToUser();
User saveResultUser = userService.addUser(user);
UserDTO result = userDTO.convertFor(saveResultUser);
return result;
}
@Override
protected User doForward(UserDTO userDTO) {
User user = new User();
BeanUtils.copyProperties(userDTO,user);
return user;
}
@Override
protected UserDTO doBackward(User user) {
throw new AssertionError("不支持逆向转化方法!");
}
}
bean的验证
为什么要验证
jsr 303验证
@NotNull
private String username;
@NotNull
private int age;
//其他代码略
}
public UserDTO addUser(@Valid UserDTO userDTO){
User user = userDTO.convertToUser();
User saveResultUser = userService.addUser(user);
UserDTO result = userDTO.convertFor(saveResultUser);
return result;
}
public UserDTO addUser(@Valid UserDTO userDTO, BindingResult bindingResult){
checkDTOParams(bindingResult);
User user = userDTO.convertToUser();
User saveResultUser = userService.addUser(user);
UserDTO result = userDTO.convertFor(saveResultUser);
return result;
}
private void checkDTOParams(BindingResult bindingResult){
if(bindingResult.hasErrors()){
//throw new 带验证码的验证错误异常
}
}
拥抱lombok
去掉Setter和Getter
@Getter
public class UserDTO {
@NotNull
private String username;
@NotNull
private int age;
public User convertToUser(){
UserDTOConvert userDTOConvert = new UserDTOConvert();
User convert = userDTOConvert.convert(this);
return convert;
}
public UserDTO convertFor(User user){
UserDTOConvert userDTOConvert = new UserDTOConvert();
UserDTO convert = userDTOConvert.reverse().convert(user);
return convert;
}
private static class UserDTOConvert extends Converter<UserDTO, User> {
@Override
protected User doForward(UserDTO userDTO) {
User user = new User();
BeanUtils.copyProperties(userDTO,user);
return user;
}
@Override
protected UserDTO doBackward(User user) {
throw new AssertionError("不支持逆向转化方法!");
}
}
}
@Data,@AllArgsConstructor,@NoArgsConstructor..这些我就不进行一一说明了，请大家自行查询资料.bean中的链式风格
private String name;
private int age;
public String getName() {
return name;
}
public Student setName(String name) {
this.name = name;
return this;
}
public int getAge() {
return age;
}
public Student setAge(int age) {
return this;
}
}
.setAge(24)
.setName("zs");
@Accessors(chain = true),看如下代码:@Setter
@Getter
public class Student {
private String name;
private int age;
}
静态构造方法
@RequiredArgsConstructor和 @NonNull）:@Setter
@Getter
@RequiredArgsConstructor(staticName = "ofName")
public class Student {
@NonNull private String name;
private int age;
}
@Setter
@Getter
@RequiredArgsConstructor(staticName = "of")
public class Student {
@NonNull private String name;
private int age;
}
使用builder
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public static Builder builder(){
return new Builder();
}
public static class Builder{
private String name;
private int age;
public Builder name(String name){
this.name = name;
return this;
}
public Builder age(int age){
this.age = age;
return this;
}
public Student build(){
Student student = new Student();
student.setAge(age);
student.setName(name);
return student;
}
}
}
public class Student {
private String name;
private int age;
}
代理模式
RestTemplate,我相信你会我和一样，对他抛出的非http状态码异常深恶痛绝。RestTemplate最为底层包装器进行包装器模式的设计:protected volatile RestTemplate restTemplate;
protected FilterRestTemplate(RestTemplate restTemplate){
this.restTemplate = restTemplate;
}
//实现RestOperations所有的接口
}
FilterRestTemplate进行包装扩展:private RestTemplate restTemplate;
public ExtractRestTemplate(RestTemplate restTemplate) {
super(restTemplate);
this.restTemplate = restTemplate;
}
public <T> RestResponseDTO<T> postForEntityWithNoException(String url, Object request, Class<T> responseType, Object... uriVariables)
throws RestClientException {
RestResponseDTO<T> restResponseDTO = new RestResponseDTO<T>();
ResponseEntity<T> tResponseEntity;
try {
tResponseEntity = restTemplate.postForEntity(url, request, responseType, uriVariables);
restResponseDTO.setData(tResponseEntity.getBody());
restResponseDTO.setMessage(tResponseEntity.getStatusCode().name());
restResponseDTO.setStatusCode(tResponseEntity.getStatusCodeValue());
}catch (Exception e){
restResponseDTO.setStatusCode(RestResponseDTO.UNKNOWN_ERROR);
restResponseDTO.setMessage(e.getMessage());
restResponseDTO.setData(null);
}
return restResponseDTO;
}
}
ExtractRestTemplate很完美的更改了异常抛出的行为，让程序更具有容错性。在这里我们不考虑ExtractRestTemplate完成的功能，让我们把焦点放在FilterRestTemplate上，“实现RestOperations所有的接口”,这个操作绝对不是一时半会可以写完的，当时在重构之前我几乎写了半个小时,如下:protected volatile RestTemplate restTemplate;
protected FilterRestTemplate(RestTemplate restTemplate) {
this.restTemplate = restTemplate;
}
@Override
public <T> T getForObject(String url, Class<T> responseType, Object... uriVariables) throws RestClientException {
return restTemplate.getForObject(url,responseType,uriVariables);
}
@Override
public <T> T getForObject(String url, Class<T> responseType, Map<String, ?> uriVariables) throws RestClientException {
return restTemplate.getForObject(url,responseType,uriVariables);
}
@Override
public <T> T getForObject(URI url, Class<T> responseType) throws RestClientException {
return restTemplate.getForObject(url,responseType);
}
@Override
public <T> ResponseEntity<T> getForEntity(String url, Class<T> responseType, Object... uriVariables) throws RestClientException {
return restTemplate.getForEntity(url,responseType,uriVariables);
}
//其他实现代码略。。。
}
@Delegate):public abstract class FilterRestTemplate implements RestOperations {
@Delegate
protected volatile RestTemplate restTemplate;
}
重构
需求案例
项目需求
思考与重构
private Date calculateDistributionTimeByOrderCreateTime(Date orderCreateTime){
DateTime orderCreateDateTime = new DateTime(orderCreateTime);
Date tomorrow = orderCreateDateTime.plusDays(1).toDate();
Date theDayAfterTomorrow = orderCreateDateTime.plusDays(2).toDate();
return orderCreateDateTime.isAfter(DISTRIBUTION_TIME_SPLIT_TIME) ? wrapDistributionTime(theDayAfterTomorrow) : wrapDistributionTime(tomorrow);
}
private Date wrapDistributionTime(Date distributionTime){
DateTime currentDistributionDateTime = new DateTime(distributionTime);
DateTime plusOneDay = currentDistributionDateTime.plusDays(1);
boolean isSunday = (DateTimeConstants.SUNDAY == currentDistributionDateTime.getDayOfWeek());
return isSunday ? plusOneDay.toDate() : currentDistributionDateTime.toDate() ;
}
提高方法
设计模式
业务驱动技术 or 技术驱动业务
代码设计
你真的优秀吗？
多看成熟框架的源码 多回头看自己的代码 勤于重构
技能
UML
类图 时序图
clean code
读者可以看一下Robert C. Martin出版的《Clean Code》（代码整洁之道） 这本书 可以参考美团文章聊聊clean code：http://tech.meituan.com/clean-code.html。 也可以看一下阿里的Java编码规范 ：https://yq.aliyun.com/articles/69327?spm=5176.100239.topwz.1.om5dRN。
linux 基础命令
总结
END
深入理解 Java 多线程核心技术
2020 年九大顶级 Java 框架如何教女朋友学 Python？
Python 2.7 ：今天起正式停用
Modified on