Step 1 Rest With Spring Boot

How to Build Rest API

  1.  Identify Resources: (/user, /user/{id})  etc.
  2.  Identify Actions (GET, POST, PUT, DELETE, PATCH etc.)
  3.  Defining Request and Response Structure
  4.  Define  Response Status( 200 as Ok, 404 as Page Not Found, 500 Internal Server Error)
  •     400 Series Errors:  Client Side Error
  •     500 Series Errors:  Server Side Error

 Best Practices for Rest API

1.Thinking on Consumer Perspective
2. validation 
3  Internationalizations -i18n
4. Exception Handling
5. HATEOAS
6. Versioning
7. Documentation 
8. Content Negotiation etc.

 Internal Working of Spring Boot


1.  How to Handle Request in Spring Boot?

Dispatcher Servlet- Front Controller Pattern

Mapping Servlets: dispatcher Servlet urls=[/]  ( as dispatcher servlet is mapped to the [/] root URL)

 

If you search for Mapping servlets you will find out the given below string in logs which is telling to you dispatcher servlet is mapped with root [/] URL



First Request Goes to the dispatcher servlet once request receive to the Dispatcher servlet than it would map the request to the right controller.

Who is Configuring Dispatcher Servlet:

With the help of autoconfiguration if you search for dispatcherservletautoconfiguration in the log



You should see a bean which is being created.

How does the Object Convert in to JSON in Spring Boot:

Step 1. request goes to dispatcher servlet.

Step 2. The dispatcher servlet would check what are the URLs.

Step 3. Then find the particular / slash and name of your URL to map the method with your Request.

Step 4. Will Execute the method and Return Object.

 

2.  How the Object convert into JSON?

There is two Important Part are involved to handle this.

1.      @ResponseBody

2.      JacksonHttpMessageConverters

@ResponseBody:

If you go inside of @RestController you will find @ResponseBody inside of RestController  interface




@ResponseBody Annotation inside of our @RestController

The default conversion, which is set up by Spring boot auto configuration, is using Jackson HTTP

 

JacksonHttpMessageConverters: it is part of Autoconfiguration.

autoConfiguation (JacksonHttpMessageConvertersConfiguration) if you search for JacksonHttpMessageConvertersConfiguration this is actually configured for REST API by spring boot



 

So the Object Conversion into JSON with the help pf @ResponseBody which is inside of our @RestController Annotations that jackSon HTTP Message Converters are auto configured by spring boot

 

 

3.  Who is configuring Error Mapping?

In given below image we have given wrong url and we got 404 error

Also says this application has no explicit mapping for /error, so you are seeing this as a fallback.

So here also error mapping handle by Autoconfiguration

Autoconfiguration (ErrorMvcAutoConfiguration)



If you search for ErrorMvcAutoConfiguration  you will find this in logs also the class will have the message which you have seen above



 

4.  How All jar is available (Spring, spring MVC, Jackson, Tomcat etc.)?

Starter Projects: spring boot started web (spring-webMvc, spring-web, spring=boot-starter-tomcat, spring-boot-starter-Json)

If you can go through Spring-boot-starter-web_VersionX.pom file

  <name>spring-boot-starter-web</name>

  <dependencies>

    <dependency>

      <groupId>org.springframework.boot</groupId>

      <artifactId>spring-boot-starter</artifactId>

      <version>3.1.0</version>

      <scope>compile</scope>

    </dependency>

    <dependency>

      <groupId>org.springframework.boot</groupId>

      <artifactId>spring-boot-starter-json</artifactId>

      <version>3.1.0</version>

      <scope>compile</scope>

    </dependency>

    <dependency>

      <groupId>org.springframework.boot</groupId>

      <artifactId>spring-boot-starter-tomcat</artifactId>

      <version>3.1.0</version>

      <scope>compile</scope>

    </dependency>

    <dependency>

      <groupId>org.springframework</groupId>

      <artifactId>spring-web</artifactId>

      <version>6.0.9</version>

      <scope>compile</scope>

    </dependency>

    <dependency>

      <groupId>org.springframework</groupId>

      <artifactId>spring-webmvc</artifactId>

      <version>6.0.9</version>

      <scope>compile</scope>

    </dependency>

  </dependencies>

</project>

 

This shows all the different dependencies jar

Tomcat, Json and other webMvc, web

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