數(shù)據(jù)訪問對(duì)象模式
數(shù)據(jù)訪問對(duì)象模式(Data Access Object Pattern)或 DAO 模式用于把低級(jí)的數(shù)據(jù)訪問 API 或操作從高級(jí)的業(yè)務(wù)服務(wù)中分離出來。以下是數(shù)據(jù)訪問對(duì)象模式的參與者。
數(shù)據(jù)訪問對(duì)象接口(Data Access Object Interface) - 該接口定義了在一個(gè)模型對(duì)象上要執(zhí)行的標(biāo)準(zhǔn)操作。
數(shù)據(jù)訪問對(duì)象實(shí)體類(Data Access Object concrete class) - 該類實(shí)現(xiàn)了上述的接口。該類負(fù)責(zé)從數(shù)據(jù)源獲取數(shù)據(jù),數(shù)據(jù)源可以是數(shù)據(jù)庫,也可以是 xml,或者是其他的存儲(chǔ)機(jī)制。
模型對(duì)象/數(shù)值對(duì)象(Model Object/Value Object) - 該對(duì)象是簡單的 POJO,包含了 get/set 方法來存儲(chǔ)通過使用 DAO 類檢索到的數(shù)據(jù)。
實(shí)現(xiàn)
我們將創(chuàng)建一個(gè)作為模型對(duì)象或數(shù)值對(duì)象的 Student 對(duì)象。StudentDao 是數(shù)據(jù)訪問對(duì)象接口。StudentDaoImpl 是實(shí)現(xiàn)了數(shù)據(jù)訪問對(duì)象接口的實(shí)體類。DaoPatternDemo,我們的演示類使用 StudentDao 來演示數(shù)據(jù)訪問對(duì)象模式的用法。

步驟 1
創(chuàng)建數(shù)值對(duì)象。
Student.java
public class Student { private String name; private int rollNo; Student(String name, int rollNo){ this.name = name; this.rollNo = rollNo; } public String getName() { return name; } public void setName(String name) { this.name = name; } public int getRollNo() { return rollNo; } public void setRollNo(int rollNo) { this.rollNo = rollNo; } }
步驟 2
創(chuàng)建數(shù)據(jù)訪問對(duì)象接口。
StudentDao.java
import java.util.List; public interface StudentDao { public List<Student> getAllStudents(); public Student getStudent(int rollNo); public void updateStudent(Student student); public void deleteStudent(Student student); }
步驟 3
創(chuàng)建實(shí)現(xiàn)了上述接口的實(shí)體類。
StudentDaoImpl.java
import java.util.ArrayList; import java.util.List; public class StudentDaoImpl implements StudentDao { //列表是當(dāng)作一個(gè)數(shù)據(jù)庫 List<Student> students; public StudentDaoImpl(){ students = new ArrayList<Student>(); Student student1 = new Student("Robert",0); Student student2 = new Student("John",1); students.add(student1); students.add(student2); } @Override public void deleteStudent(Student student) { students.remove(student.getRollNo()); System.out.println("Student: Roll No " + student.getRollNo() +", deleted from database"); } //從數(shù)據(jù)庫中檢索學(xué)生名單 @Override public List<Student> getAllStudents() { return students; } @Override public Student getStudent(int rollNo) { return students.get(rollNo); } @Override public void updateStudent(Student student) { students.get(student.getRollNo()).setName(student.getName()); System.out.println("Student: Roll No " + student.getRollNo() +", updated in the database"); } }
步驟 4
使用 StudentDao 來演示數(shù)據(jù)訪問對(duì)象模式的用法。
CompositeEntityPatternDemo.java
public class DaoPatternDemo { public static void main(String[] args) { StudentDao studentDao = new StudentDaoImpl(); //輸出所有的學(xué)生 for (Student student : studentDao.getAllStudents()) { System.out.println("Student: [RollNo : " +student.getRollNo()+", Name : "+student.getName()+" ]"); } //更新學(xué)生 Student student =studentDao.getAllStudents().get(0); student.setName("Michael"); studentDao.updateStudent(student); //獲取學(xué)生 studentDao.getStudent(0); System.out.println("Student: [RollNo : " +student.getRollNo()+", Name : "+student.getName()+" ]"); } }
步驟 5
驗(yàn)證輸出。
Student: [RollNo : 0, Name : Robert ] Student: [RollNo : 1, Name : John ] Student: Roll No 0, updated in the database Student: [RollNo : 0, Name : Michael ]