JDBC---数据库连接增删改查

到这里，我意识到这个系统MVC中的C放置在各个V中了，所以C就不介绍了，哈哈哈
接着总结DAO层，这个系统我采用的应该算是标准的DAO设计模式
还没有完全写完的dao包



DAO的结构图



DAO数据访问层的开发：
1.设计基类DAOBase类
提供标准的获得和关闭数据库连接的方法

package com.yinger.patientims.dao;

import java.sql.Connection;

import java.sql.DriverManager;

/**

* 数据库操作的基础类，它是其他的DAO类的父类

* 定义了建立数据库连接和关闭数据库连接的方法

*/

public
class DAOBase {

private Connection connection;

// 得到数据库连接

public Connection getConnection() {

try {

Class.forName("com.mysql.jdbc.Driver");

connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/patientims","root",
"root");

} catch (Exception e) {

e.printStackTrace();

}

return connection;

}

// 关闭数据库连接

public
void closeConnnection() {

try {

connection.close();

} catch (Exception e) {

e.printStackTrace();

} finally {

if (connection
!= null) {

connection = null;

}

}

}

}

2.编写各个Model层对象对应的DAO类
例如 PatientDAO
注意一个方法 setOnePatient 方法，这个方法很有用的，其作用是将数据库中取出的一条记录放置到一个Patient对象上，所以该方法
最好是能够独立出来，以便重复使用！

package com.yinger.patientims.dao;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.ArrayList;

import java.util.List;

import com.yinger.patientims.model.Patient;

import com.yinger.patientims.util.DBUtil;

public
class PatientDAO extends DAOBase {

// 得到所有住院的病人的信息

// SELECT

// p.id,p.name,p.age,p.sex,p.address,p.logtime,p.phone,d.name,b.sickbedno,r.sickroomno

// FROM t_patient p,t_department d,t_sickbed b,t_sickroom r

// WHERE p.sickbed_id=b.id and b.sickroom_id=r.id and r.department_id=d.id

public List<Patient> getPatientInfoList() {

Patient patient;

List<Patient> list=
new ArrayList<Patient>();

// 注意：这里有两个name，要使用到别名

String sql = "SELECT p.id,p.name as pname,p.age,p.sex,p.address,p.logtime,p.phone,d.name as dname,b.sickbedno,r.sickroomno "

+ "FROM t_patient p,t_department d,t_sickbed b,t_sickroom r "

+ "WHERE p.sickbed_id=b.id and b.sickroom_id=r.id and r.department_id=d.id";

String sql="SELECT * FROM t_table" //查询整个表

Connection connection = null;

// 在finally中使用它是它必须要初始化

// 还有，它一定要放在外面，这样在try外面（finally）才可以被访问到

// 还有，一定要有finally！关闭数据库连接是很重要的！

try {

connection = getConnection();

PreparedStatement pStatement = connection.prepareStatement(sql);

ResultSet resultSet = pStatement.executeQuery();

while (resultSet.next()) {

patient = setOnePatient(resultSet);

list.add(patient);

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

connection.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

return list;

}

// 将数据库中的一条patient记录关联到一个Patient对象中

// 并且它不处理异常，抛出由上层处理

private Patient setOnePatient(ResultSet resultSet)throws Exception {

Patient patient =
new Patient();

if (resultSet.getLong("id")!=
0) {

patient.setId(resultSet.getLong("id"));

}

if (resultSet.getString("pname")!= null) {

patient.setName(resultSet.getString("pname"));

}

if (resultSet.getString("sex")!= null) {

patient.setSex(resultSet.getString("sex"));

}

if (resultSet.getString("phone")!= null) {

patient.setPhone(resultSet.getString("phone"));

}

if (resultSet.getString("address")!= null) {

patient.setAddress(resultSet.getString("address"));

}

if (resultSet.getInt("age")!=
0) {

patient.setAge(resultSet.getInt("age"));

}

if (resultSet.getDate("logtime")!= null) {

patient.setLogtime(resultSet.getDate("logtime"));

}

if (resultSet.getString("dname")!= null) {

// 注意这一步！这里容易发生空指针异常！在一个Patient对象中Department等属性并没有被初始化！

// 所以要在类中new出各个对象，对于SickRoom等等同理

patient.getDepartment().setName(resultSet.getString("dname"));

}

if (resultSet.getInt("sickbedno")!=
0) {

patient.getSickbed().setSickBedNo(resultSet.getInt("sickbedno"));

}

if (resultSet.getInt("sickroomno")!=
0) {

patient.getSickroom().setSickRoomNo(resultSet.getInt("sickroomno"));

}

return patient;

}

// 删除病人信息

public
boolean deletePatient(Patient patient) {

Long id = patient.getId();

Connection connection = null;

String sql = "delete from t_patient where id=
"+ id + " ";

try {

connection = getConnection();

PreparedStatement pStatement = connection.prepareStatement(sql);

int res
= pStatement.executeUpdate();

if (res
> 0) {

return true;
// 注意：这里虽然是return了，但是这个方法真正返回之前还是要执行finally

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

connection.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

return false;

}

// 添加病人住院信息

public
boolean insertPatient(Patient patient) {

Connection connection = null;

// INSERT INTO

// t_patient(name,sex,age,phone,logtime,address,sickbed_id) VALUES

// ('patient"+i+"','女',37,'1533535354','2011-10-10','TianJin',"+id+")

String sql = "INSERT INTO t_patient(name,sex,age,phone,logtime,address,sickbed_id) VALUES ('"+ patient.getName()
+ "','"
+ patient.getSex()+
"',"

+ patient.getAge()
+ ",'" + patient.getPhone()+
"','" +
DBUtil.simpleDateFormat.format(patient.getLogtime()) +
"','" + patient.getAddress()+
"',"

+ patient.getSickbed().getId()
+ ")"; //字符串用'"+ patient.getName() + "'，整形用"+ patient.getAge() + "

//patient.getLogtime().toLocaleString() 已经不推荐使用了

//注意：时间是有点特别地是使用 DateFormater进行format一下！

try {

connection = getConnection();

PreparedStatement pStatement = connection.prepareStatement(sql);

int res
= pStatement.executeUpdate();

if (res
> 0) {

return true;
// 注意：这里虽然是return了，但是这个方法真正返回之前还是要执行finally

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

connection.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

return false;

}

// 修改病人住院信息

public
boolean updatePatient(Patient patient) {

Connection connection = null;

//UPDATE t_patient as p set p.name='yyh' , p.address='ghalsdhgl' , p.age=24 , p.phone='523659365', p.sex='female'

// where id=6

StringBuffer sql =
new StringBuffer("UPDATE t_patient as p ");

sql.append(" set p.name='"+patient.getName()+"' ");

sql.append(", p.address='"+patient.getAddress()+"' ");

sql.append(" , p.age="+patient.getAge()+" ");

sql.append(" , p.phone='"+patient.getPhone()+"' ");

sql.append(", p.sex='"+patient.getSex()+"' ");

sql.append(" ,p.sickbed_id= "+patient.getSickbed().getId()+" ");

sql.append(" where id="+patient.getId());

try {

connection = getConnection();

PreparedStatement pStatement = connection.prepareStatement(sql.toString());

int res
= pStatement.executeUpdate();

if (res
> 0) {

return true;

}

} catch (Exception e) {

e.printStackTrace();

} finally {

try {

connection.close();

} catch (SQLException e) {

e.printStackTrace();

}

}

return false;

}

}

再比如：DepartmentDAO类

package com.yinger.patientims.dao;

import java.sql.Connection;

import java.sql.PreparedStatement;

import java.sql.ResultSet;

import java.sql.SQLException;

import java.util.ArrayList;

import java.util.List;

import com.yinger.patientims.model.Department;

public
class DepartmentDAO extends DAOBase{

// private List departmentList = new ArrayList();

// private Department department;

// 得到所有的科室

public List<Department> getDepartmentList(){

Department department;

List<Department> list=
new ArrayList<Department>();

Connection connection = null;

String sql = "select id,name from t_department";

try {

connection = getConnection();

PreparedStatement pStatement = connection.prepareStatement(sql);

ResultSet resultSet = pStatement.executeQuery();

while (resultSet.next()) {

department = setOneDepartment(resultSet);

list.add(department);

}

pStatement.close();

} catch (Exception e) {

e.printStackTrace();

} finally{

try {

connection.close();// Quick Fix : Ctrl + 1

} catch (SQLException e) {

e.printStackTrace();

}

}

return list;

}

// 从数据库中取出一条记录并保存到一个Department中

private Department setOneDepartment(ResultSet resultSet)throws Exception {

Department department =
new Department();

if(resultSet.getLong("id")!=0){

department.setId(resultSet.getLong("id"));

}

if(resultSet.getString("name")!=null){

department.setName(resultSet.getString("name"));

}

return department;

}

}

3.总结：
（1）注意DAO类中每个操作的语句结构，一定要捕捉异常进行处理，一定要有finally，并在其中关闭连接
（2）注意数据库中取出来的数据的类型和Model的该属性的类型
（3）注意方法的返回值，是否要返回值？
（4）注意sql语句的构造，如果多次使用字符串的合并建议使用高效率的StringBuilder，还有构造时也要注意是否需要''，这个最好是
先测试，然后编写代码！

参考：/article/5004762.html