java-to-nextjs

Java to Next.js TypeScript Conversion

Overview

Converts Java 1.8 classes to TypeScript 5.0+ interface definitions for Next.js 14+. Output as markdown code blocks only — never modify project files.

Core Constraint

CRITICAL: Output TypeScript interface definitions as markdown code blocks only. Do NOT modify, edit, or alter any project files.

Type Mapping

Java Type	TypeScript Type
int / Integer / long / Long	number
float / Float / double / Double	number
boolean / Boolean	boolean
String	string
BigDecimal / decimal	string (default) or number (with @BigDecimalToNumber)
Date	string (ISO 8601)
Timestamp	number (unix) or string (ISO, with @TimestampFormat)
List<T>	T[]
Map<K,V>	Record<K, V>
Object / JSONObject	Record<string, any>

Nullability Rules

Java Annotation	TypeScript
@NonNull / @NotNull	Required field (name: string)
No annotation / @Nullable	Optional field (name?: string)

Default: All properties are optional unless explicitly marked non-null.

Naming Conventions

Interface names: PascalCase with meaningful suffixes (SaveEmailData, LoginRequest, UserProfileResponse)

Property names: ⚠️ KEEP IDENTICAL TO JAVA/API — do NOT convert between camelCase and snake_case.

// ✅ Correct
interface SaveEmailData {
  inviteCode: string;     // matches API
  invite_url?: string;    // preserves snake_case
}

// ❌ Wrong
interface SaveEmailData {
  InviteCode: string;     // changed to PascalCase
  inviteUrl?: string;     // changed snake_case to camelCase
}

Inheritance Handling

1. Identify parent classes and trace the full chain
2. If parent is BaseReq or BaseResponse → EXCLUDE all their properties (handled by HTTP middleware)
3. Choose approach:
   • Interface Extension (recommended): use extends when parent is reused across multiple children
   • Flattened Interface: copy all properties into one interface when standalone

Documentation

Migrate Java comments to TypeScript preserving original language:

• Chinese comments → keep Chinese
• English comments → keep English
• Use JSDoc (/** */) for interfaces, inline // for properties

Step-by-Step Workflow

1. Analyze Java class — properties, annotations, types, inheritance
2. If inheritance exists → read parent class files
3. Handle BaseReq/BaseResponse exclusion if applicable
4. Create interface with PascalCase name
5. Apply type mapping (including @BigDecimalToNumber, @TimestampFormat)
6. Apply nullability (@NonNull → required, else optional)
7. Preserve property names exactly as in API
8. Migrate comments preserving original language

Validation Checklist

• [ ] @NonNull/@NotNull properties are required (no ?)
• [ ] All other properties are optional (?)
• [ ] Interface uses PascalCase naming
• [ ] Property names match API contract exactly
• [ ] Inheritance detected and parent classes analyzed
• [ ] BaseReq/BaseResponse properties excluded if applicable
• [ ] Type mappings correct (especially BigDecimal, Date, arrays)
• [ ] Documentation migrated in original language
• [ ] Output is markdown code block only (no file modifications)