JDBC之: ORM基本思想(七)
ORM(Object RelationShip Mapping)的基本思想
-
表结构跟类对应;表中的字段和类的属性对应;表中的记录和对象对应
-
让javabean的属性名和类型尽量和数据库保持一致
-
一条记录对应一个对象,将这些查询到的对象放到容器中
-
将表中的一条记录封装到Object数组中
-
将表中的一条记录封装到map中
-
将表中一条记录封装到javabean对象中
封装连接和关闭
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
public class JDBCUtil {
//用于读取资源文件中的信息
static Properties pros = null;
//加载JDBCUtil类的时候调用
static {
pros = new Properties();
try {
pros.load(Thread.currentThread().getContextClassLoader()
.getResourceAsStream("db.properties"));
} catch (IOException e) {
e.printStackTrace();
}
}
public static Connection getConnection(){
try {
Class.forName(pros.getProperty("Driver"));
return DriverManager.getConnection(pros.getProperty("Url"),
pros.getProperty("User"),
pros.getProperty("Password"));
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
return null;
}
public static void close(ResultSet rs,Statement st,Connection conn){
try {
if(rs!=null){
rs.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(st!=null){
st.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(conn!=null){
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}使用Object数组封装一条记录
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
/**
* 测试使用Object[]来封装一条记录
* 使用List<Object[]>存储多条记录
* @author Matrix42
*
*/
public class Demo01 {
public static void main(String[] args) {
Connection conn = JDBCUtil.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;
Object[] obj = null;
List<Object[]> list = new ArrayList<Object[]>();
//Alt+Shift+Z add try-catch block
try {
ps = conn.prepareStatement("select empname,salary,age from emp where id = ?");
ps.setObject(1, 1);
rs = ps.executeQuery();
while(rs.next()){
//System.out.println(rs.getString("empname"));
obj = new Object[3];
//一个Object封装一条数据
//多条可以用容器
obj[0] = rs.getObject(1);
obj[1] = rs.getObject(2);
obj[2] = rs.getObject(3);
list.add(obj);
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
JDBCUtil.close(rs, ps, conn);
}
//连接关闭后还可以获取内容
for (Object[] objs : list) {
System.out.println(""+objs[0]+"\n"+objs[1]+"\n"+objs[2]);
}
}
}使用Map封装一条记录
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* 测试使用Map来封装一条记录
* 使用List<Map>存储多条记录
* @author Matrix42
*
*/
public class Demo02 {
public static void main(String[] args) {
Connection conn = JDBCUtil.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;
//使用一个Map封装一条记录
List<Map<String, Object>> list = new ArrayList<Map<String, Object>>();
//Alt+Shift+Z add try-catch block
try {
ps = conn.prepareStatement("select empname,salary,age from emp where id < ?");
ps.setObject(1, 3);
rs = ps.executeQuery();
while(rs.next()){
Map<String, Object> row = new HashMap<String, Object>();
row.put("empname", rs.getObject(1));
row.put("salary", rs.getObject(2));
row.put("age", rs.getObject(3));
list.add(row);
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
JDBCUtil.close(rs, ps, conn);
}
//连接关闭后还可以获取内容
for (Map<String, Object> map : list) {
System.out.println(map.get("empname"));
System.out.println(map.get("salary"));
System.out.println(map.get("age"));
}
}
}使用javabean对象封装一条记录
import java.sql.Date;
//表和类对应
/**
* emp表的javabean
* @author Matrix42
*
*/
public class Emp {
private Integer id;
private String empname;
private Double salary;
private Date birthday;
private Integer age;
private Integer deptId;
//javabean一定要有空构造器
public Emp() {
super();
}
public Emp(String empname, Double salary, Date birthday,
Integer age, Integer deptId) {
super();
this.empname = empname;
this.salary = salary;
this.birthday = birthday;
this.age = age;
this.deptId = deptId;
}
public Emp(Integer id, String empname, Double salary, Date birthday,
Integer age, Integer deptId) {
super();
this.id = id;
this.empname = empname;
this.salary = salary;
this.birthday = birthday;
this.age = age;
this.deptId = deptId;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getEmpname() {
return empname;
}
public void setEmpname(String empname) {
this.empname = empname;
}
public Double getSalary() {
return salary;
}
public void setSalary(Double salary) {
this.salary = salary;
}
public Date getBirthday() {
return birthday;
}
public void setBirthday(Date birthday) {
this.birthday = birthday;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
public Integer getDeptId() {
return deptId;
}
public void setDeptId(Integer deptId) {
this.deptId = deptId;
}
//方便打印
@Override
public String toString() {
return "Emp [id=" + id + ", empname=" + empname + ", salary=" + salary
+ ", birthday=" + birthday + ", age=" + age + ", deptId="
+ deptId + "]";
}
}/**
* dept表的javabean
* @author Matrix42
*
*/
public class Dept {
private Integer id;
private String address;
private String dname;
public Dept() {
super();
}
public Dept(String address, String dname) {
super();
this.address = address;
this.dname = dname;
}
public Dept(Integer id, String address, String dname) {
super();
this.id = id;
this.address = address;
this.dname = dname;
}
public Integer getId() {
return id;
}
public void setId(Integer id) {
this.id = id;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public String getDname() {
return dname;
}
public void setDname(String dname) {
this.dname = dname;
}
}import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;
/**
* 测试使用javabean来封装一条记录
* 使用List<javabean>存储多条记录
* @author Matrix42
*
*/
public class Demo03 {
public static void main(String[] args) {
Connection conn = JDBCUtil.getConnection();
PreparedStatement ps = null;
ResultSet rs = null;
//使用一个Map封装一条记录
List<Emp> list = new ArrayList<Emp>();
//Alt+Shift+Z add try-catch block
try {
ps = conn.prepareStatement("select empname,salary,age from emp where id < ?");
ps.setObject(1, 3);
rs = ps.executeQuery();
while(rs.next()){
Emp emp = new Emp(rs.getString(1),rs.getDouble(2),null,rs.getInt(3),null);
list.add(emp);
}
} catch (SQLException e) {
e.printStackTrace();
}finally{
JDBCUtil.close(rs, ps, conn);
}
//连接关闭后还可以获取内容
for (Emp emp : list) {
System.out.println(emp);
}
}
}