Spring Boot - 02 MVC

This is the second post in a series of posts to cover different aspects of Spring Boot. Please note that the entire post isn’t necessarily only written in English.

In this post, I am going to cover the basics of Spring Web MVC.

Web MVC

How to display model data & process form input

Template view:

JSP pages (main/WEB-INF)
Thymeleaf (main/resources/templates)

Disable template cache:

spring.thymeleaf.cache = false (add this to application.properties)

(Remember to set back to True in production)
Use DevTools (auto disable cache in dev env, auto enable in production env)

Domain

Debug: Also need to add lombok extension in IDE.

Lombok: Auto generate getter & setter methods and constructors, based on all final properties

@Data

// 这个 annotation 可以不要，因为 @Data 会自动创建相关 constructor
@RequiredArgsConstructor	
public class Ingredient {

    private final String id;
    private final String name;
    private final Type type;

    public static enum Type {
        WRAP, PROTEIN, VEGGIES, CHEESE, SAUCE
    }
}

Related dependency:

<dependency>
    <groupId>org.projectlombok</groupId>
    <artifactId>lombok</artifactId>
    <optional>true</optional>
</dependency>

Controller

Handle HTTP requests from client

Handling GET requests

// Logger
@Slf4j

// Component scan
@Controller	

// at class level, specify the path
@RequestMapping("/design")	
public class DesignTacoController {

    // Only use @RequestMapping at class level. Use new annotations here
    @GetMapping		
    public String showDesignForm(Model model) {

        List<Ingredient> ingredients = Arrays.asList(
                new Ingredient("FLTO", "Flour Tortilla", Type.WRAP),
                new Ingredient("SRCR", "Sour Cream", Type.SAUCE) );

        Type[] types = Ingredient.Type.values();
        for (Type type : types)
            model.addAttribute(type.toString().toLowerCase(), filterByType(ingredients, type));

        model.addAttribute("design", new Taco());
        
        // return view name "design" (ressources/templates/design.html)
        return "design";	
    }
    
    private List<Ingredient> filterByType(List<Ingredient> ingredients, Type type) {
        return ingredients.stream()
                .filter(x -> x.getType().equals(type))
                .collect(Collectors.toList());
    }
}

@Slf4j: Simple Logging Facade for Java.

Lombok-provided annotation, auto generate logger at runtime

@GetMapping & class-level @RequestMapping:

When /design receives a HTTP GET request, showDesignForm() will be called to handle the request

@GetMapping: New in Spring 4.3. Old method:

1 2	// lazy way, leave off the method attribute @RequestMapping(method = RequestMethod.GET)

All request-mapping annotations:

@RequestMapping

@GetMapping

@PostMapping

@PutMapping

@DeleteMapping

@PatchMapping

Model: an object that transfers data between controller & view. ??

Data placed in Model attributes is copied into the servlet response attributes, where the view can find them

Handling POST request

Fields in the form are bound to properties of a Taco object

@PostMapping

// Taco passed as a parameter in processDesign
public String processDesign(Taco taco) {	
    
    // log for input data processing
    log.info("Processing design: " + taco);	
    
    // redirection，直接跳转到 /orders/current
    return "redirect:/orders/current";	
}

Validate Form Input

The clumsy way: litter the controller with a bunch of if / then

Recommended: Java Bean Validation API (JSR-303)

Validation API & its Hibernate implementation are auto added to the project as transient dependencies in the web starter.

Steps to apply validation:

Declare validation rules in domain classes
Specify validation should be performed in controller methods with @PostMapping
Modify views to display validation errors

Example 1

Taco domain:

@Data
public class Taco {

    @NotNull
    @Size(min=5, message="Name must be at least 5 characters long")
    private String name;

    @Size(min=1, message="You must choose at least 1 ingredient")
    private List<String> ingredients;
}

Taco controller (添加 validation):

@PostMapping

// 这里不一样
public String processDesign(@Valid Taco taco, Errors errors) {	
    
	// 还有这里，如果出错，redisplay the form
	if (errors.hasErrors())	
		return "design";		
    
	// 如果没有出错，再用 log
	log.info("Processing design: " + taco);	
	return "redirect:/orders/current";
}

Example 2

Order excerpt:

// Only make sure this isn't blank
@NotBlank(message="Name is required")
private String name;

// Annotation here: Hibernate 自带!   —— 算法： Luhn algorithm check
@CreditCardNumber(message="Not a valid credit card number")
private String ccNumber;

// Note the regex here! For validating Credit Card exp. date!
@Pattern(regexp="^(0[1-9]|1[0-2])([\\/])([1-9][0-9])$", message="Must be formatted MM/YY")
private String ccExpiration;

Order controller:

@PostMapping
public String processDesign(@Valid Taco taco, Errors errors) {
    
    // 这一句是模板
    if (errors.hasErrors())							
        return "design";
    
    log.info("Processing design: " + taco);
    return "redirect:/orders/current";
}

View Controllers

The controllers written so far:

All annotated with @Controller: auto discovered by Spring component scanning, and instantiated as beans in the context
All annotated with @GetMapping, @PostMapping: specify which method should handle what requests

A view controller: does not process data / input, only forward the GET request to a view

Create a new config class for each kind of configuration (e.g. web, data, security)

@Configuration

// WebMvcConfigurer interface
public class WebConfig implements WebMvcConfigurer {			
    
    // need to override
    @Override		
    
    // void!
    public void addViewControllers(ViewControllerRegistry registry) {		
        registry.addViewController("/").setViewName("home");	
    }
}

Registry: register one or more view controllers