ORM的使用

ORM(Object Relationship Mapping）的基本思想
表结构跟类对应；
表中字段和类的属性对应；
表中记录和对象对应；

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（List，Set，Map）

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
将表中的一条记录封装到javabean对象中**

示例1：将表中的一条记录封装到Object数组中

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;/** * 使用Object数组来封装一条记录 * @author liguodong * */public class Demo01 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        Object[] objects = null;        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            objects = new Object[3];//一个Object数组封装了一条记录的信息！            while(resultSet.next())            {                //System.out.println(resultSet.getString(1));                objects[0] = resultSet.getObject(1);                objects[1] = resultSet.getObject(2);                objects[2] = resultSet.getObject(3);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        System.out.println(objects[0]+"--"+objects[1]+"--"+objects[2]);         }}

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;/** * 使用List<Object[]>存储多条记录 * @author liguodong * */public class Demo02 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        //存放多条记录        List<Object[]> list = new ArrayList<Object[]>();        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id>=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                Object[] objects = new Object[3];//一个Object数组封装了一条记录的信息！                //System.out.println(resultSet.getString(1));                objects[0] = resultSet.getObject(1);                objects[1] = resultSet.getObject(2);                objects[2] = resultSet.getObject(3);                list.add(objects);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }           for (Object[] objects : list) {            System.out.println(objects[0]+"--"+objects[1]+"--"+objects[2]);        }    }}

运行结果：
王二狗–30000.0–4
李大钊–35000.0–5

示例2：将表中的一条记录封装到map中

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.HashMap;import java.util.Map;/** * 使用map来封装一条记录 * @author liguodong * */public class Demo03 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        Map<String,Object> map = new HashMap<String, Object>();//使用一个map封装了一条记录的信息！        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                //System.out.println(resultSet.getString(1));                map.put("empname", resultSet.getObject(1));                map.put("salary", resultSet.getObject(2));                map.put("age", resultSet.getObject(3));            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        //遍历Map，就是遍历这一行的多列的信息        for (String key : map.keySet()) {            System.out.println(key+"--"+map.get(key)+"\t");        }    }}

运行结果：
age–4
empname–王二狗
salary–30000.0

package com.lgd.orm;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;/** * 使用List<Map<String,Object>>来封装多条记录 * @author liguodong * */public class Demo04 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        List<Map<String,Object>> list = new ArrayList<Map<String,Object>>();        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id>=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                Map<String,Object> map = new HashMap<String, Object>();//使用一个map封装了一条记录的信息！                //System.out.println(resultSet.getString(1));                map.put("empname", resultSet.getObject(1));                map.put("salary", resultSet.getObject(2));                map.put("age", resultSet.getObject(3));                list.add(map);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        //遍历List<Map<String,Object>>        for (Map<String, Object> map : list) {            for (String key : map.keySet()) {                System.out.print(key+":"+map.get(key)+"\t");            }               System.out.println();        }    }}

运行结果：
age:4 empname:王二狗 salary:30000.0
age:5 empname:李大钊 salary:35000.0

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.HashMap;import java.util.Map;/** * 使用Map<Integer,Map<String,Object>>来封装多条记录 * @author liguodong * */public class Demo05 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        Map<Integer,Map<String,Object>> maps = new HashMap<Integer,Map<String,Object>>();        try {            preparedStatement = connection.prepareStatement("select id,enpname,salary,age from emp where id>=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                Map<String,Object> map = new HashMap<String, Object>();//使用一个map封装了一条记录的信息！                //System.out.println(resultSet.getString(1));                map.put("empname", resultSet.getObject(2));                map.put("salary", resultSet.getObject(3));                map.put("age", resultSet.getObject(4));                maps.put((Integer)resultSet.getObject(1),map);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        //遍历Map<Integer,Map<String,Object>>        for (Integer id : maps.keySet()) {            for (String key : maps.get(id).keySet()) {                System.out.print(key+":"+maps.get(id).get(key)+"\t");            }               System.out.println();        }    }}

运行结果：
age:4 empname:王二狗 salary:30000.0
age:5 empname:李大钊 salary:35000.0

示例3：将表中的一条记录封装到javabean对象中

package com.lgd.orm;import java.sql.Date;public class Emp { //表结构和类对应    private Integer id;    private String empname;    private Integer age;    private Double salary;    private Date birthday;    private Integer 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 Integer getAge() {        return age;    }    public void setAge(Integer age) {        this.age = age;    }    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 getDeptId() {        return deptId;    }    public void setDeptId(Integer deptId) {        this.deptId = deptId;    }    public Emp(Integer id, String empname, Integer age, Double salary,            Date birthday, Integer deptId) {        super();        this.id = id;        this.empname = empname;        this.age = age;        this.salary = salary;        this.birthday = birthday;        this.deptId = deptId;    }    public Emp(String empname, Double salary, Integer age) {        super();        this.empname = empname;        this.age = age;        this.salary = salary;    }    public Emp() {    }}

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.HashMap;import java.util.Map;/** * 使用Javabean来封装一条记录 * @author liguodong * */public class Demo06 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        Emp emp = null;        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                //System.out.println(resultSet.getString(1));                emp = new Emp(resultSet.getString(1), resultSet.getDouble(2), resultSet.getInt(3));                         }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        System.out.println(emp.getEmpname()+"--"+emp.getSalary()+"--"+emp.getAge());                }}

运行结果：
王二狗–30000.0–4

package com.lgd.orm;import java.sql.Connection;import java.sql.PreparedStatement;import java.sql.ResultSet;import java.sql.SQLException;import java.util.ArrayList;import java.util.List;/** * 使用List<Emp>来封装多条记录 * @author liguodong * */public class Demo07 {    public static void main(String[] args) {        Connection connection = JDBCUtil2.getMysqlConn();        PreparedStatement preparedStatement = null;        ResultSet resultSet = null;        List<Emp> list = new ArrayList<Emp>();        try {            preparedStatement = connection.prepareStatement("select enpname,salary,age from emp where id>=?");            //preparedStatement.setObject(1, 2);            preparedStatement.setInt(1, 2);            resultSet = preparedStatement.executeQuery();            while(resultSet.next())            {                //System.out.println(resultSet.getString(1));                Emp emp = new Emp(resultSet.getString(1), resultSet.getDouble(2), resultSet.getInt(3));                             list.add(emp);            }        } catch (SQLException e) {            e.printStackTrace();        }finally{            JDBCUtil2.close(resultSet,preparedStatement,connection);        }        for (Emp emp : list) {            System.out.println(emp.getEmpname()+"--"+emp.getSalary()+"--"+emp.getAge());        }    }}

运行结果：
王二狗–30000.0–4
李大钊–35000.0–5