定义

UML类图

简单实现

最基本的数据访问程序

User表

public class User {
    private int id;
    private String name;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

SqlServerUser类

public class SqlServerUser {
    private static final String TAG = "SqlServerUser";
    public void insertUser(User user){
        Log.d(TAG, "insert: 在SQL Server中录入一个用户记录");
    }

    public User getUser(int id){
        Log.d(TAG, "getUser: 在SQL Server中获取一个用户记录");
        return null;
    }
}

客户端调用

    User user = new User();
    user.setId(1);
    user.setName("Allever");
    SqlServerUser sqlServerUser = new SqlServerUser();
    sqlServerUser.insertUser(user);
    sqlServerUser.getUser(1);

如果换为MySQL数据库改动就很多

使用工厂方法改进

IUser接口

public interface IUser {
    void insertUser(User user);
    User getUser(int id);
}

SqlServerUser类

public class SqlServerUser implements IUser {

    private static final String TAG = "SqlServerUser";
    @Override
    public void insertUser(User user){
        Log.d(TAG, "insert: 在SQL Server中录入一个用户记录");
    }

    @Override
    public User getUser(int id){
        Log.d(TAG, "getUser: 在SQL Server中获取一个用户记录");
        return null;
    }
}

MySQLUser类

public class MySQLUser implements IUser {
    private static final String TAG = "MySQLUser";
    @Override
    public void insertUser(User user){
        Log.d(TAG, "insert: 在MySQL Server中录入一个用户记录");
    }

    @Override
    public User getUser(int id){
        Log.d(TAG, "getUser: 在MySQL Server中获取一个用户记录");
        return null;
    }
}

IFactory抽象工厂接口

public interface IFactory {
    IUser createUser();
}

SqlServerFactory具体工厂类

public class SqlServerFactory implements IFactory {
    @Override
    public IUser createUser() {
        return new SqlServerUser();
    }
}

MySQLServerFactory具体工厂

public class MySQLServerFactory implements IFactory {
    @Override
    public IUser createUser() {
        return new MySQLUser();
    }
}

客户端调用

        User user = new User();
        user.setId(1);
        user.setName("Allever");

        IFactory factory = new SqlServerFactory();
        IUser iUser = factory.createUser();
        iUser.insertUser(user);
        iUser.getUser(1);

如果改为MySQL数据库，这改动这里

IFactory factory = new MySQLServerFactory();

使用抽象工厂

新增Department表

public class Department {
    private int id;
    private String deptName;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getDeptName() {
        return deptName;
    }

    public void setDeptName(String deptName) {
        this.deptName = deptName;
    }
}

新增IDepartment接口

public interface IDepartment {
    void insertDepartment(Department department);
    Department getDepartment(int id);
}

新增SqlServerDepartment类

public class SqlServerDepartment implements IDepartment {
    private static final String TAG = "SqlServerDepartment";
    @Override
    public void insertDepartment(Department department) {
        Log.d(TAG, "insertDepartment: 在Sql Server 中插入Department");
    }

    @Override
    public Department getDepartment(int id) {
        Log.d(TAG, "insertDepartment: 在Sql Server 中获取Department");
        return null;
    }
}

新增MySQLDepartment类

public class MySQLDepartment implements IDepartment {
    private static final String TAG = "MySQLDepartment";
    @Override
    public void insertDepartment(Department department) {
        Log.d(TAG, "insertDepartment: 在MySQL 中插入Department");
    }

    @Override
    public Department getDepartment(int id) {
        Log.d(TAG, "insertDepartment: 在MySQL 中获取Department");
        return null;
    }
}

修改IFactory接口

public interface IFactory {
    IUser createUser();
    IDepartment createDepartment(); //新增
}

修改SqlServerFactory类

public class SqlServerFactory implements IFactory {
    @Override
    public IUser createUser() {
        return new SqlServerUser();
    }

    @Override
    public IDepartment createDepartment() {
        return new SqlServerDepartment();
    }
}

修改MySQLServerFactory类

public class MySQLServerFactory implements IFactory {
    @Override
    public IUser createUser() {
        return new MySQLUser();
    }

    @Override
    public IDepartment createDepartment() {
        return new MySQLDepartment();
    }
}

客户端调用

        User user = new User();
        user.setId(1);
        user.setName("Allever");
        Department department = new Department();
        department.setId(1);
        department.setDeptName("Computer");

        IFactory factory = new MySQLServerFactory();
        IUser iUser = factory.createUser();
        iUser.insertUser(user);
        iUser.getUser(1);
        
        IDepartment iDepartment = factory.createDepartment();
        iDepartment.insertDepartment(department);
        iDepartment.getDepartment(1);

总结

只有一个User类和User操作类的时候，只需要工厂方法模式， 但现在数据库中有很多表， 而SQL Server 和 MySQL 又是两大不同的分类， 所以解决这种涉及到多个产品系列的时候，就要用到抽象工厂模式。