Spring Boot: Failed to Configure a DataSource ('url' Not Specified)
Fix 'Failed to configure a DataSource: url attribute is not specified' in Spring Boot 3 by setting the URL, adding the driver or a profile.
~8 min readread →
Developer interview notes & guides — Page 4
Focused explanations and longer guides, with worked scenarios, common mistakes and interview exercises across every chapter.
level:
Showing 73–96 of 200 articles
Jackson Infinite Recursion with JPA Entities in Spring Boot
Fix 'Could not write JSON: Infinite recursion (StackOverflowError)' for bidirectional JPA entities in Spring Boot 3 with DTOs or annotations.
~7 min readread →
Spring Boot: No Qualifying Bean of Type (Could Not Be Found)
Fix 'required a bean of type that could not be found' and 'No qualifying bean' in Spring Boot 3: scanning, conditions, qualifiers, tests.
~7 min readread →
Web Server Failed to Start: Port 8080 Was Already in Use
Fix 'Web server failed to start. Port 8080 was already in use' in Spring Boot: find the process on the port, stop it or change server.port.
~7 min readread →
Whitelabel Error Page 404 in Spring Boot: How to Fix It
Seeing the Whitelabel Error Page with status 404 in Spring Boot 3? Check the mapping, component scan, @RestController and context path.
~7 min readread →
PostgreSQL 'operator does not exist': Fixing Type Mismatches
Fix PostgreSQL 'operator does not exist: integer = text': read the operand types, cast the constant or parameter, and fix the column type at the source.
~8 min readread →
TypeScript TS2345: Not Assignable to Parameter of Type 'never'
Fix TS2345 'Argument of type string is not assignable to parameter of type never' from empty arrays, function unions and exhaustive checks.
~7 min readread →
TS2307: Cannot Find Module or Its Type Declarations in TypeScript
Fix TS2307 'Cannot find module or its corresponding type declarations' and TS7016 by tracing module resolution, @types, paths and exports.
~8 min readread →
TS7053: Element Implicitly Has an 'any' Type in TypeScript
Fix TS7053 'Element implicitly has an any type because expression of type string can't be used to index type' with keyof, Record and guards.
~7 min readread →
TS2532: Object Is Possibly 'undefined' (and TS18048) in TypeScript
Fix TS2532 'Object is possibly undefined' and TS18048 by finding where undefined enters the type, then narrowing or failing early.
~8 min readread →
TS2339: Property 'x' Does Not Exist on Type 'Y' in TypeScript
Fix TS2339 'Property does not exist on type' for unions, empty objects, DOM elements and window globals without casting to any.
~7 min readread →
TS2322: Type 'X' Is Not Assignable to Type 'Y' in TypeScript
Fix TS2322 'Type X is not assignable to type Y' by reading the elaboration chain from the bottom and correcting the value, not casting.
~7 min readread →
Node.js Events and Listener Ordering
Trace synchronous EventEmitter delivery, listener order and once(), and fix the event that fires before anyone is listening for it.
~7 min readread →
React Deferred Results and Stale UI
Keep a search input responsive with useDeferredValue, show users when results are stale, and see why memo is required and fetches aren't reduced.
~6 min readread →
Angular Async Validators and Pending State
A username-availability check traced step by step: PENDING status, cancelled checks, debouncing, errors that hang the form, and safe submit.
~6 min readread →
Angular Component Tests That Verify Behavior
Test an Angular component through its DOM, inputs, outputs and HTTP calls, so refactors pass and real bugs fail. Five tests, run and broken.
~6 min readread →
Angular Content Projection with ng-content and ng-template
Why projected content is created by the parent even inside a closed @if, how select slots match, and when ng-template makes projection lazy.
~6 min readread →
Angular Custom Controls and Value Accessors
A star-rating ControlValueAccessor, built and then broken: what writeValue, onChange, onTouched and setDisabledState each must do.
~6 min readread →
Angular providedIn root vs Component Providers vs viewProviders
Where a service is provided decides who shares it: providedIn root, component providers, viewProviders and route providers, with instance ids.
~6 min readread →
Angular Lazy Loading Routes: Why Your Lazy Feature Isn't Lazy
How one innocent import moved a lazy feature into the initial bundle (233 kB to 407 kB), and how to draw boundaries that keep lazy routes lazy.
~6 min readread →
Angular OnPush and Input Reference Changes
Why an OnPush child ignores user.role = 'admin' but updates for a new object, what else marks it dirty, and how signal inputs change the picture.
~6 min readread →
Angular Reactive Forms: patchValue vs setValue and Lost Edits
Who owns the edit state in an Angular reactive form: loading server data with patchValue, splitting subforms, avoiding echo loops and lost edits.
~6 min readread →
Angular Route Guards and Server Authorization
Route guards decide what the Angular router shows, not what a user may do. Why the admin chunk is still public and where the real check belongs.
~7 min readread →
Angular Route Parameters and Reused Components
Going from /products/1 to /products/2 reuses the component, so snapshot reads go stale. Read params with paramMap, toSignal or input binding.
~6 min readread →
No notes match that… try another filter.