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：http://www.cnblogs.com/yinger/archive/2011/11/19/2255660.html