@PreAuthorize annotation in Spring Boot - Step-by-Step Execution

Concept Flow - @PreAuthorize annotation

Method call request

↓

Check @PreAuthorize expression

↓

Allow method

↓

Return result

When a method is called, Spring checks the @PreAuthorize expression. If true, it runs the method; if false, it blocks access.

Execution Sample

Spring Boot

@PreAuthorize("hasRole('ADMIN')")
public void deleteUser() {
  // delete logic
}

This code allows only users with ADMIN role to run deleteUser method.

Execution Table

Step	Action	Expression Evaluated	Result	Method Access
1	User calls deleteUser()	hasRole('ADMIN')	true	Allowed
2	Method deleteUser() runs	-	-	User deleted
3	User calls deleteUser()	hasRole('ADMIN')	false	Denied
4	Access denied exception thrown	-	-	Access denied

💡 Execution stops when access is denied or method completes.

Variable Tracker

Variable	Start	After Step 1	After Step 3	Final
UserRole	unknown	ADMIN	USER	unchanged
AccessGranted	false	true	false	depends on role

Key Moments - 2 Insights

Why does the method not run when the user role is not ADMIN?

Because at Step 3 in execution_table, the expression hasRole('ADMIN') evaluates to false, so access is denied before method runs.

What happens if the @PreAuthorize expression is true?

At Step 1, if the expression is true, the method runs normally as shown in Step 2.

Visual Quiz - 3 Questions

Look at the execution_table, what is the method access result at Step 3?

A Allowed

B Denied

C Throws error after method runs

D Method runs partially

💡 Hint

Check the 'Method Access' column at Step 3 in execution_table.

At which step does the method actually execute?

A Step 3

B Step 1

C Step 2

D Step 4

💡 Hint

Look for 'Method deleteUser() runs' in the Action column.

If the user role changes from USER to ADMIN, how does AccessGranted change in variable_tracker?

A Changes from false to true

B Changes from true to false

C Remains false

D Remains true

💡 Hint

Compare AccessGranted values after Step 1 and Step 3 in variable_tracker.

Concept Snapshot

@PreAuthorize("expression")
- Checks security before method runs
- Expression uses roles or permissions
- If true, method runs
- If false, access denied exception
- Used for method-level security in Spring

Full Transcript

The @PreAuthorize annotation in Spring Boot checks a security expression before a method runs. When a method is called, Spring evaluates the expression inside @PreAuthorize. If the expression returns true, the method executes normally. If false, Spring blocks access and throws an exception. For example, @PreAuthorize("hasRole('ADMIN')") allows only users with ADMIN role to run the method. The execution table shows steps where the expression is checked and access is granted or denied. Variables like UserRole and AccessGranted track the user's role and whether access is allowed. This helps secure methods by role or permission checks before running sensitive code.