ইনভার্শন অব কন্ট্রোল নীতি

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public class UserService {
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    private final JdbcUserRepository userRepository = new JdbcUserRepository();
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    private final MD5PasswordEncryption passwordEncryption = new MD5PasswordEncryption();
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    public User saveUser(User user) {
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        user.setPassword(passwordEncryption.encrypt(user.getPassword()));
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        return userRepository.save(user);
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    }
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}

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public interface UserRepository {
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    User save(User user);
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}
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public class JdbcUserRepository implements UserRepository {
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    @Override
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    public User save(User user) {
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        // store user in database
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        return user;
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    }
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}
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public class RemoteUserRepository implements UserRepository{
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    @Override
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    public User save(User user) {
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        // send user in other server
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        return user;
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    }
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}

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public interface PasswordEncryption {
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    String encrypt(String password);
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}
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public class MD5PasswordEncryption implements PasswordEncryption {
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    @Override
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    public String encrypt(String password) {
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        // implement password encryption using MD5
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        return password;
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    }
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}
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public class Sha256PasswordEncryption implements PasswordEncryption{
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    @Override
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    public String encrypt(String password) {
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        // implement password encryption using SHA 256
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        return password;
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    }
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}

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public class UserService {
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    private final UserRepository userRepository;
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    private final PasswordEncryption passwordEncryption;
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    public UserService(UserRepository userRepository, PasswordEncryption passwordEncryption) {
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        this.userRepository = userRepository;
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        this.passwordEncryption = passwordEncryption;
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    }
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    public User saveUser(User user) {
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        user.setPassword(passwordEncryption.encrypt(user.getPassword()));
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        return userRepository.save(user);
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    }
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}

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UserService userService = new UserService(
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    new JdbcUserRepository(),
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    new MD5PasswordEncryption()
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);

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UserService userService = new UserService(
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    new JdbcUserRepository(),
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    new Sha256PasswordEncryption()
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);