Java Secure coding guidelines

Identify and apply Java secure coding practices to reduce vulnerabilities, protect sensitive data, and harden application behaviour against common attack vectors.

What is covered in this Skill?

• Input validation: type, length, format, and range checks
• SQL/OS/LDAP injection defence via PreparedStatement and parameterized APIs
• Attack surface minimisation: least-privilege permissions, removal of unused features
• Strong cryptography: BCrypt/Argon2 for passwords, AES-GCM for encryption, digital signatures; avoid deprecated ciphers (MD5, SHA-1, DES)
• Secure exception handling: log diagnostic details internally, expose only generic messages to clients
• Secrets management: load credentials from environment variables or secret managers — never hardcoded
• Safe deserialization: strict allow-lists, prefer explicit DTOs over native Java serialization
• Output encoding to prevent XSS in rendered content

Scope: The reference is organized by examples (good/bad code patterns) for each core area. Apply recommendations based on applicable examples.

Constraints

Before applying any secure coding changes, ensure the project compiles. If compilation fails, stop immediately — do not proceed until resolved. After applying improvements, run full verification.

• MANDATORY: Run ./mvnw compile or mvn compile before applying any changes
• SAFETY: If compilation fails, stop immediately — do not proceed until the project is in a valid state
• VERIFY: Run ./mvnw clean verify or mvn clean verify after applying improvements
• BEFORE APPLYING: Read the reference for detailed good/bad examples, constraints, and safeguards for each secure coding pattern

When to use this skill

• Review Java code for secure coding

Reference

For detailed guidance, examples, and constraints, see references/124-java-secure-coding.md.