Content type negotiation in Spring Boot - Step-by-Step Execution

Concept Flow - Content type negotiation

Client sends HTTP request

↓

Server checks Accept header

↓

Match supported content types?

No→Respond 406 Not Acceptable

Yes↓

Select best content type

↓

Serialize response data accordingly

↓

Send HTTP response with Content-Type header

The server reads the client's Accept header, chooses a supported content type, serializes the response, and sends it back with the correct Content-Type.

Execution Sample

Spring Boot

  @GetMapping(value = "/data", produces = {"application/json", "application/xml"})
  public Data getData() {
      return new Data("Hello", 123);
  }

This Spring Boot controller method returns data in JSON or XML depending on the client's Accept header.

Execution Table

Step	Client Accept Header	Server Action	Selected Content-Type	Response Body Format
1	application/json	Check if application/json supported	application/json	JSON serialized data
2	application/xml	Check if application/xml supported	application/xml	XML serialized data
3	text/html	No matching supported type	None	Respond 406 Not Acceptable

💡 Execution stops when a matching content type is found or 406 error is returned if none match.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3
Accept Header	None	application/json	application/xml	text/html
Selected Content-Type	None	application/json	application/xml	None
Response Status	None	200 OK	200 OK	406 Not Acceptable

Key Moments - 2 Insights

Why does the server respond with 406 Not Acceptable sometimes?

Because the client's Accept header requests a content type the server does not support, as shown in step 3 of the execution_table.

How does the server decide which content type to use when multiple are supported?

The server matches the client's Accept header in order and picks the first supported type, as seen in steps 1 and 2 of the execution_table.

Visual Quiz - 3 Questions

Look at the execution_table, what content type is selected when the client sends 'application/xml'?

A text/html

B application/json

C application/xml

D 406 Not Acceptable

💡 Hint

Check row 2 under 'Selected Content-Type' in the execution_table.

At which step does the server respond with 406 Not Acceptable?

A Step 3

B Step 1

C Step 2

D Never

💡 Hint

Look at the 'Response Status' column in variable_tracker after Step 3.

If the client sends 'application/json, application/xml', which content type will the server choose?

A application/xml

B application/json

C text/html

D 406 Not Acceptable

💡 Hint

Server picks the first supported type matching the Accept header, see execution_table steps 1 and 2.

Concept Snapshot

Content type negotiation in Spring Boot:
- Client sends Accept header with preferred types
- Server checks supported types in @GetMapping produces
- Matches Accept header to supported types
- Serializes response accordingly
- Sends response with matching Content-Type
- If no match, responds 406 Not Acceptable

Full Transcript

Content type negotiation is how a Spring Boot server decides what format to send data in. The client sends an HTTP request with an Accept header listing preferred content types like JSON or XML. The server looks at this header and compares it to the types it can produce, defined in the @GetMapping annotation's produces attribute. If the server supports one of the requested types, it serializes the response data in that format and sends it back with the correct Content-Type header. If none match, the server responds with a 406 Not Acceptable status. This process ensures the client gets data in a format it understands.