@Intercepts({
    @Signature(type = StatementHandler.class, method = "prepare", args = {Connection.class, Integer.class})
})
@Component
public class SoftDeleteInterceptor implements Interceptor {
    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        StatementHandler handler = (StatementHandler) invocation.getTarget();
        BoundSql boundSql = handler.getBoundSql();
        String originalSql = boundSql.getSql();
        
        // Append soft delete condition to all SELECT queries
        String modifiedSql = originalSql.replace("WHERE 1=1", "WHERE 1=1 AND is_deleted = 0");
        
        // Update the SQL statement through reflection
        Field sqlField = boundSql.getClass().getDeclaredField("sql");
        sqlField.setAccessible(true);
        sqlField.set(boundSql, modifiedSql);
        
        return invocation.proceed();
    }
}

Register the interceptor in Spring configuration:

@Configuration
public class WebMvcConfig implements WebMvcConfigurer {
    
    @Autowired
    private SoftDeleteInterceptor softDeleteInterceptor;
    
    @Autowired
    private AuthenticationInterceptor authInterceptor;
    
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        registry.addInterceptor(softDeleteInterceptor);
        registry.addInterceptor(authInterceptor)
                .excludePathPatterns("/auth/login", "/auth/register");
    }
}

For implmeenting soft delete functionality:

• Use @DeleteMapping in controlelrs
• Employ <update> statements in maper XML files

User availability validation example:

public boolean checkUsernameAvailability(String username) {
    User existingUser = userRepository.findByUsername(username);
    return existingUser == null || existingUser.isDeleted();
}

public User createUser(User newUser) {
    if (checkUsernameAvailability(newUser.getUsername())) {
        return userRepository.save(newUser);
    } else {
        throw new UsernameConflictException("Username already taken");
    }
}