纯Java代码模拟Hibernate一级缓存原理，简单易懂。

复制代码 代码如下:
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public class LevelOneCache {
//这个对象就是用来模拟hibernate一级缓存的
private static Map<Integer, Student> stus=new HashMap<Integer, Student>();

public static void main(String[] args) {
getStudent(1);
getStudent(1);
getStudent(1);
getStudent(2);
getStudent(2);
}

public static Student getStudent(Integer id){
if(stus.containsKey(id)){
System.out.println("从缓存中取数据");
return stus.get(id);
} else {
System.out.println("从数据库中取数据");
Student s=MyDB.getStudentById(id);
//将从数据库中取得的数据放入缓存
stus.put(id, s);
return s;
}
}
}
//模拟数据库
class MyDB{
private static List<Student> list=new ArrayList<Student>();
static{
Student s1=new Student();
s1.setName("Name1");
s1.setId(1);
Student s2=new Student();
s2.setName("Name2");
s2.setId(2);
Student s3=new Student();
s3.setName("Name3");
s3.setId(3);
//初始化数据库
list.add(s1);
list.add(s2);
list.add(s3);
}
//数据库中提供公共的查询方法
public static Student getStudentById(Integer id){
for(Student s:list){
if(s.getId().equals(id)){
return s;
}
}
//查询不到则返回空
return null;
}
}

//domain对象
class Student{
private Integer id;
private String name;
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}