Bootstrap

SpringBoot注解总结

@SpringBootApplication

Controller层

@Controller(返回的是页面)

@RestController（返回字符串）等于@Controller+@ResponseBody

@RequestMapping

不携带数据给前端，只是实现前端路由

@Controller//在Spring中注册，表示本类是一个控制器类
public class ViewController {
    @RequestMapping("toview")//完整路径url http://localhost:8080/toview
    public String view(){
        return "test.html";//且本html静态文件存放在resource目录下的static目录下
    }
}

#根据上面return的是一个具体的格式文件，由于我们后面可能用到的是其他的模板（不是html）这样就会使得需要修改大量文件
#所以我们采用配置文件的方式。在配置文件中指定文件格式，return的时候只return文件名就可以了
spring.mvc.view.prefix=/
spring.mvc.view.suffix=.html

//然后控制层我们可以这样写
@Controller//在Spring中注册，表示本类是一个控制器类
public class ViewController {
    @RequestMapping("toview")//完整路径url http://localhost:8080/toview
    public String view(){
        return "test";//且本html静态文件存放在resource目录下的static目录下
    }
}

携带数据给前端页面—使用（freemarker模板引擎）

<!--将携带给前端的数据解析显示出来-->
<!--FreeMarker模板引擎-->
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-freemarker</artifactId>
</dependency>

#freeMarker
#后缀
spring.freemarker.suffix=.html
spring.freemarker.template-loader-path=classpath:/static/

@RequestMapping("bringdata")
public ModelAndView data(){
    ModelAndView view = new ModelAndView("test");
    view.addObject("str1","hello world");
    view.addObject("str2","数据带来了");
    return view;
}

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <hr/>
    <div>${str1}</div>
    <hr/>
    <div>${str2}</div>
    </body>
</html>

携带数据给前端页面—使用（thymeleaf模板引擎）

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
    <version>2.5.2</version>
</dependency>

spring.thymeleaf.check-template=false
spring.thymeleaf.check-template-location=false

@RequestMapping("bringdata")
public String data(Model model){
    model.addAttribute("str1","hello world");
    model.addAttribute("str2","数据带来了");
    return "test";
}

<!--前端页面放在resources目录下的templates目录下-->
<!DOCTYPE html>
<html lang="en">
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
    <hr/>
    <div th:text="${str1}"></div>
    <hr/>
    <div th:text="${str2}"></div>
    </body>
</html>

@RequestParam

前端携带参数给后端（前端URL采用？的形式）

@Controller
public class ParamsController {
    @RequestMapping("param")
    public String toparam(@RequestParam("num") int num, Model model){
  //可以不穿参数，给参数设置默认值为0。
  //public String toparam(@RequestParam(value = "num",required = false,defaultValue = "0") int num, Model model){
  //传入多参
  //public String toparam(@RequestParam(value = "num",required = false,defaultValue = "0") int num,@RequestParam(value = "str",required = false,defaultValue = "") String str， Model model){
        //if(str.equals("测试")){}//String最好要指定默认值，不然不传值为null那么条件判断会报错。
        System.out.println("num = "+num);
        model.addAttribute("num",num);
        return "numpage";
    }
}

<!--url: http://localhost:8080/param?num=1024-->
<!--numpage.html-->
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
  <div th:text="${num}"></div>
</body>
</html>

@PathVariable

@Controller
public class ParamsController {
    @RequestMapping("path/{id}/{type}")
    public String topath(@PathVariable(required = false) int id,
                         @PathVariable(required = false) String type,Model model){
        System.out.println("id="+id);
        System.out.println("type="+type);
        model.addAttribute("id",id);
        model.addAttribute("type",type);
        return "restfull";
    }
}

<!DOCTYPE html>
<html lang="en">
<html xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
  <div th:text="${id}"></div>
  <div th:text="${type}"></div>
</body>
</html>

@GetMapping（查询数据）

//与RestController配合，将获得的数据返回到浏览器（没有具体的页面）。
@RestController
@RequestMapping("rest")
public class RestFullController {
    //查询数据没有参数，url没有指定二级目录,可以返回任意类型。
    @GetMapping  //http:localhost:8080/rest
    public String test(){
        return "test";
    }
    //查询数据没有参数，url指定二级目录,可以返回任意类型。
    @GetMapping("get") //http:localhost:8080/rest/get
    public String get(){
        return "我是返回数据";
    }
    //查询数据没有参数，url指定二级目录,可以返回任意类型（返回对象）。
    @GetMapping("/getuser")
    public User getuser(){
        User user = new User(1, "张山", "男", 18);
        return user;
    }
    //查询数据携带参数，url指定二级目录,可以返回任意类型（返回对象）。
    @GetMapping("{id}")
    public User getuserbyid(@PathVariable("id") int id){
        User user = new User(id, "李四", "女", 21);
        return user;
    }
}

@
public class User {
    private int id;
    private String name;
    private String sex;
    private int age;   
}

@PostMapping（新增数据）

@RestController
@RequestMapping("rest")
public class RestFullController {
    @GetMapping//http:localhost:8080/rest
    public String getFindUser(@RequestBody int id){
        User user = service.findeUserById(id);
        return user;
    }
    //与get的请求url都一样但是方式不一样
    @PostMapping//http:localhost:8080/rest
    public User postAddUser (@RequestBody User user){
        System.out.println(user);
        return user;
    }
}

@PutMapping（与上面原理一致）

@DeleteMapping（与上面原理一致）

@ResponseBody(@ResponseBody+@Controller==@RestController)

@Controller
@ResponseBody
public class TestController {
    @GetMapping("controller")
    public String testController(){
        return "testController";
    }
}
//与下面的一模一样，其实RestController注解与Controller注解唯一的区别就是RestController里面含有ResponseBody注解
@RestController
public class TestRestController {
    @GetMapping("restcontroller")
    public String testRestController(){
        return "testRestController";
    }
}

@RequestBody

//前端将一个对象封装成json的格式传到后端，后端用与之对应的实体类接受需要加上本注解
@RestController
@RequestMapping("rest")
public class RestFullController {   
	@PostMapping//http:localhost:8080/rest
    public User postAddUser (@RequestBody User user){
        System.out.println(user);
        return user;
    }
}

@CrossOrigin(解决跨域问题)（最好的解决跨域的方式是使用过滤器）

@RestController
@RequestMapping("rest")
public class RestFullController {   
	@PostMapping//http:localhost:8080/rest
    @CrossOrigin
    public User postAddUser (@RequestBody User user){
        System.out.println(user);
        return user;
    }
}

Service层

在讲下面之前先看一下几个例子

//service层的接口
public interface UserService {
    public User get();
    public User getUserById(int id);
}

//service层的实现类
public class UserServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("UserServiceImpl"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("getUserById:"+user);
        return user;
    }
}

//controller层
@RestController
@RequestMapping("/action")
public class UserActionController {
    private UserService userService;
    @GetMapping
    public User get(){
        userService = new UserServiceImpl();
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        userService = new UserServiceImpl();
        User userById = userService.getUserById(id);
        return userById;
    }
}

我们可以发现一个问题，在controller层调用service层的时候，我们在controller层使用了一个关于service层的全局变量，然后再在具体的方法里面重新赋值。当然我们也可以在全局变量的位置写全，如 private UserServiceImpl userService = new UserServiceImpl();
但是这些方法都不是很好，我们可以使用@Service注解在Service实现层里面，将本类在Spring中注册bean，然后在Controller层全局变量的地方使用@Autowrired注解将获取注册的bean。如下所示

@Service（bean的注册）+@Autowired（获取bean）

//service层的实现类
@Service
public class UserServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("UserServiceImpl"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("getUserById:"+user);
        return user;
    }
}

//controller层
@RestController
@RequestMapping("/action")
public class UserActionController {
    @Autowired
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = userService.getUserById(id);
        return userById;
    }
}

@Component（bean的注册）(与@Service @Controller @Repository)都是一样的，主要的作用是视觉上区分各层。而@Component表示组件，可能在任意层被调用。

@Autowired（获取bean）

@Resource（获取bean）

//如果service层有多个实现类实现一个接口（这就是我们为什么我们在Controller层使用多态的形式，很方便转换我们service层的实现）
//接口
public interface UserService {
    public User get();
    public User getUserById(int id);
}
//接口实现1
@Service
public class UserServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("UserServiceImpl---get:"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("UserServiceImpl---getUserById:"+user);
        return user;
    }
}
//接口实现2
@Service
public class LoginServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("LoginServiceImpl---get:"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("LoginServiceImpl---getUserById:"+user);
        return user;
    }
}

//那么问题来了，我Controller层如何去判断我现在想用哪一个service实现
//在目前情况（俩个实现类实现一个接口的情况下），使用@Autowired注解会在编译前直接报错。
@RestController
@RequestMapping("/action")
public class UserActionController {
    @Autowired
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = userService.getUserById(id);
        return userById;
    }
}
//在目前情况（俩个实现类实现一个接口的情况下），使用@Resource注解会在编译时报错。
@RestController
@RequestMapping("/action")
public class UserActionController {
    @Resource
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = userService.getUserById(id);
        return userById;
    }
}

//在目前情况（俩个实现类实现一个接口的情况下），正确方法。
@RestController
@RequestMapping("/action")
public class UserActionController {
    @Resource(name="loginServiceImpl")//指定具体哪个类，并且类的首字母小写
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = userService.getUserById(id);
        return userById;
    }
}

//还可以同时写多个
@RestController
@RequestMapping("/action")
public class UserActionController {
    //  1
    @Resource(name = "loginServiceImpl")
    private UserService loginService;
    //  2 
    @Resource(name = "userServiceImpl")
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = loginService.getUserById(id);
        return userById;
    }
}

@Autowired+@Qualifier（获取bean）

//如果一个接口有多个实现类，并且非要想使用@Autowired注解，那么可以配合@Qualifier注解使用
@RestController
@RequestMapping("/action")
public class UserActionController {
//    @Resource(name = "loginServiceImpl")
    @Autowired
    @Qualifier("loginServiceImpl")
    private UserService loginService;
    @Resource(name = "userServiceImpl")
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = loginService.getUserById(id);
        return userById;
    }
}

@Configuration+@Bean（bean的注册）（人为）

//如果Service层不用@Service注解注册Service层的bean，我们可以创建一个配置类进行手动配置
//接口
public interface UserService {
    public User get();
    public User getUserById(int id);
}
//实现类1
public class LoginServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("LoginServiceImpl---get:"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("LoginServiceImpl---getUserById:"+user);
        return user;
    }
}
//实现类2
public class UserServiceImpl implements UserService{
    @Override
    public User get() {
        User user = new User(1, "张山", "男", 18);
        System.out.println("UserServiceImpl---get:"+user);
        return user;
    }
    @Override
    public User getUserById(@PathVariable("id") int id) {
        User user = new User(id, "李四", "女", 24);
        System.out.println("UserServiceImpl---getUserById:"+user);
        return user;
    }
}

//手动配置
@Configuration
public class MyBeans {
    @Bean
    public UserService loginServiceImpl(){
        return new LoginServiceImpl();
    }
    @Bean
    public UserService userServiceImpl(){
        return new UserServiceImpl();
    }
}

@RestController
@RequestMapping("/action")
public class UserActionController {
//    @Resource(name = "loginServiceImpl")
    @Autowired
    @Qualifier("loginServiceImpl")
    private UserService loginService;
    @Resource(name = "userServiceImpl")
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = loginService.getUserById(id);
        return userById;
    }
}

//如果想换名字

//方法一

//手动配置
@Configuration
public class MyBeans {
    @Bean
    public UserService login(){
        return new LoginServiceImpl();
    }
    @Bean
    public UserService userServiceImpl(){
        return new UserServiceImpl();
    }
}

@RestController
@RequestMapping("/action")
public class UserActionController {
//    @Resource(name = "loginServiceImpl")
    @Autowired
    @Qualifier("login")
    private UserService loginService;
    @Resource(name = "userServiceImpl")
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = loginService.getUserById(id);
        return userById;
    }
}

//方法二

//手动配置
@Configuration
public class MyBeans {
    @Bean(name="loginAdmin")
    public UserService login(){
        return new LoginServiceImpl();
    }
    @Bean
    public UserService userServiceImpl(){
        return new UserServiceImpl();
    }
}

@RestController
@RequestMapping("/action")
public class UserActionController {
//    @Resource(name = "loginServiceImpl")
    @Autowired
    @Qualifier("loginAdmin")
    private UserService loginService;
    @Resource(name = "userServiceImpl")
    private UserService userService;
    @GetMapping
    public User get(){
        User user = userService.get();
        return user;
    }
    @GetMapping("{id}")
    public User getUserById(@PathVariable("id") int id){
        User userById = loginService.getUserById(id);
        return userById;
    }
}

@Values

view.page=view
local.username=wwy
local.password=123456

@RestController
@RequestMapping("/action")
public class UserActionController {
    @Value("${view.page}")
    private String page;
    @Value("${local.username}")
    private String username;
    @Value("${local.password}")
    private String password;
    @GetMapping("val")
    public String getValue(){
        return "page="+page+" , username="+username+" , password="+password;
    }
}

悦读

道可道，非常道；名可名，非常名。 无名，天地之始，有名，万物之母。 故常无欲，以观其妙，常有欲，以观其徼。 此两者，同出而异名，同谓之玄，玄之又玄，众妙之门。

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