目标

绝对不使用字段注入

绝对不多写一行多余代码

绝对不少写一行必要代码

项目文件

项目结构.png

使用字段注入

@RestController
@RequestMapping("/users")
public class UserController {
    // 此处 idea会有黄色的警告,因为使用了字段注入
    @Autowired
    private UserService userService;
    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        final User user = userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到"+userId);
        }
        return user;
    }
}

使用构造器注入

@RestController
@RequestMapping("/users")
public class UserController {

    private  final UserService userService;
   // spring4.3之后如果一个类只有一个构造器,可不加任何注入相关注解
   //@Autowired
   public UserController(UserService userService) {
          this.userService = userservice;
   }
    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        final User user = userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到"+userId);
        }
        return user;
    }
}

使用@RequiredArgsConstructor注入必须依赖

@RestController
@RequestMapping("/users")
@RequiredArgsConstructor //会自动生成一个所有final字段的构造函数
public class UserController {
   //建议所有必须依赖都加final
    private  final UserService userService;
    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        final User user = userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到"+userId);
        }
        return user;
    }
}

使用@FieldDefaults添加字段修饰符

@RestController
@RequestMapping("/users")
@RequiredArgsConstructor //会自动生成一个所有final字段的构造函数
@FieldDefaults(makeFinal = true, // 设置所有字段为final
level = AccessLevel.PRIVATE) // 设置所有字段为private
public class UserController {
   //建议所有必须依赖都加final
    UserService userService;
    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        final User user = userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到"+userId);
        }
        return user;
    }
}

利用@Setter @Nullable和@NonFinal注入可选依赖

@RestController
@RequestMapping("/users")
@RequiredArgsConstructor
@Slf4j
@FieldDefaults(makeFinal = true, level = AccessLevel.PRIVATE)
public class UserController {
    UserService userService;
    // 这个注解是spring5.0之后加入和注解
    @Nullable
    @NotBlank
    @NonFinal // 排除@FieldDefaults设置的fianl修饰符
   //在 setSmsSender方法上生命@Autowired}
    @Setter(onMethod_ = {@Autowired
// 这个可加可不加,详见生成后文件(required = false)
}) 
    SmsSender smsSender;

    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        final User user = userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到" + userId);
        }
        return user;
    }

    @PostMapping("sms-send")
    public void sendSms(@RequestParam String phone, @RequestParam String content) {
        sendSmsIfAvailable(phone, content);
    }

    private void sendSmsIfAvailable(String phone, String content) {
        if (smsSender != null) {
            smsSender.sender(phone, content);
        } else {
            log.info("向手机号:{} 发送内容:{}", phone, content);
        }
    }
}

最终生成的文件

import cn.len.article.spring01.domain.User;
import cn.len.article.spring01.service.UserService;
import cn.len.article.spring01.vendor.SmsSender;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.lang.Nullable;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.server.ResponseStatusException;

import javax.validation.constraints.NotBlank;
@RestController
@RequestMapping({"/users"})
public class UserController {
    private static final Logger log = LoggerFactory.getLogger(UserController.class);
    // 非静态字段加上了private和final修饰符
    private final UserService userService;
    @Nullable
    @NotBlank
    private SmsSender smsSender;

    @GetMapping({"{userId}"})
    public User me(@PathVariable String userId) {
        User user = this.userService.findById(userId);
        if (user == null) {
            throw new ResponseStatusException(HttpStatus.NOT_FOUND, "未找到" + userId);
        } else {
            return user;
        }
    }

    @PostMapping({"sms-send"})
    public void sendSms(@RequestParam String phone, @RequestParam String content) {
        this.sendSmsIfAvailable(phone, content);
    }

    private void sendSmsIfAvailable(String phone, String content) {
        if (this.smsSender != null) {
            this.smsSender.sender(phone, content);
        } else {
            log.info("向手机号:{} 发送内容:{}", phone, content);
        }

    }
    // 由lombok的@RequiredArgsConstructor生成的唯一构造器
    public UserController(final UserService userService) {
        this.userService = userService;
    }

    @Autowired
    // 在spring5.0之后被Optional 或@Nullable作用的参数注入是可选的
    // 我们并没有在上面的@Setter在参数上声明任何注解,但是处理过的文件却有@Nullable这个注解
    // 可能是因为放在字段上的@Nullable上面注解了jsr305的 @Nonnull注解,lombok做了特殊处理
    // jsr validator的@NotBlank注解并没有出现在参数里面
    public void setSmsSender(@Nullable final SmsSender smsSender) {
        this.smsSender = smsSender;
    }
}