Analysis and practice of parameter parser handlermethodargumentresolver

Spring Parameter resolver –HandlerMethodArgumentResolver Analysis and actual combat

analysis

Since we need to analyze it , Take a look at this interface first

public interface HandlerMethodArgumentResolver {
    
    boolean supportsParameter(MethodParameter var1);

    @Nullable
    Object resolveArgument(MethodParameter var1, @Nullable ModelAndViewContainer var2, NativeWebRequest var3, @Nullable WebDataBinderFactory var4) throws Exception;
}

There are two ways to interface supportsParameter and resolveArgument.

Method supportsParameter Well understood. , The return value is boolean type , Its function is to judge Controller Parameters in layer , Whether the conditions are met , If the conditions are met, execute resolveArgument Method , If you are not satisfied, skip .

and resolveArgument Methods? , It's only in supportsParameter Method returns true It will be called . Used to handle some business , Assign return value to Controller This parameter in the layer .

therefore , We can HandlerMethodArgumentResolver Understood as a parameter parser , We can implement... By writing a class HandlerMethodArgumentResolver Interface to implement Controller Initialization of method parameters in the layer .

actual combat

When the parameter parser is not used Controller controller ：

@RestController
@RequestMapping("/build/project")
public class BuildSmProjectController extends BaseController {
    

	@Autowired
	private BuildSmProjectService buildSmProjectService;
    
    @Autowired
	private RedisUtils redis;

	@GetMapping("list")
	public R list(@RequestHeader("token") String token, BuildSmProject buildSmProject) {
    
		startPage();
        SysUser sysUser = redis.get(Constants.ACCESS_TOKEN + token, SysUser.class);
		buildSmProject.setTenantId(sysUser.getTenantId());
		return result(buildSmProjectService.selectBuildSmProjectList(buildSmProject));
	}
} 

list In the method , In order to obtain SysUser object , You need to get it in the user request header token, Then go to redis Get system user information . Just want to get user information , Will inevitably repeat the above code .

Next use HandlerMethodArgumentResolver Interface to perform a small optimization .

---

Use HandlerMethodArgumentResolver After the parser ：

First make a custom annotation , Identification is used to parse user information

@Target(ElementType.PARAMETER)
@Retention(RetentionPolicy.RUNTIME)
public @interface LoginUser
{
    
}

Next, write a class implementation HandlerMethodArgumentResolver Interface

@Component
public class LoginUserHandlerResolver implements HandlerMethodArgumentResolver {
    

	@Autowired
	private RedisUtils redis;

    //  Judge whether the parameter is SysUser Class and whether there is @LoginUser annotation , return true perform resolveArgument Method 
	@Override
	public boolean supportsParameter(MethodParameter parameter) {
    
		return parameter.getParameterType().isAssignableFrom(SysUser.class)
				&& parameter.hasParameterAnnotation(LoginUser.class);
	}

    //  This method mainly obtains the request header parameters token, Get token Go to redis obtain SysUser The information is assigned to the above parameters 
	@Override
	public Object resolveArgument(MethodParameter parameter, ModelAndViewContainer container, NativeWebRequest nativeWebRequest, WebDataBinderFactory factory) {
    
		String token = ServletUtils.getHeader("token");
		return redis.get(Constants.ACCESS_TOKEN + token, SysUser.class);
	}

}

Put the class we wrote , Add to spring In the parser

@Configuration
public class WebMvcConfig implements WebMvcConfigurer
{
    
    @Autowired
    private LoginUserHandlerResolver loginUserHandlerResolver;

    @Override
    public void addArgumentResolvers(List<HandlerMethodArgumentResolver> argumentResolvers)
    {
    
        argumentResolvers.add(loginUserHandlerResolver);
    }
}

So our control class can be written like this ：

@RestController
@RequestMapping("/build/project")
public class BuildSmProjectController extends BaseController {
    

	@Autowired
	private BuildSmProjectService buildSmProjectService;

	@GetMapping("list")
	public R list(@LoginUser SysUser sysUser, BuildSmProject buildSmProject) {
    
		startPage();
		buildSmProject.setTenantId(sysUser.getTenantId());
		return result(buildSmProjectService.selectBuildSmProjectList(buildSmProject));
	}
} 

Next, as long as the method wants to obtain user information, it only needs to request the current login user on the header token, write @LoginUser SysUser sysUser You can directly obtain the user information and assign it to sysUser, Reduce the writing of some redundant code .