前言
在前面的博文中JDBC基础使用写增删改查会出现很多重复代码，可以将重复代码提取出来。
一、设计JDBC
- 层次结构：
- 项目结构：
二、BaseDao
2.1、将资源提取到文件
- 在database.properties中将需要的资源放入其中：
mysqlDriver=com.mysql.cj.jdbc.Driver
mysqlUrl=jdbc:mysql://192.168.136.204:3306/jdbcdb
mysqlUser=root
mysqlPwd=root
- 创建一个jdbc的基层类BaseDao(读取配置文件放入其中)：
private static String mysqlDriver;
private static String mysqlUrl;
private static String mysqlUser;
private static String mysqlPwd;
static {
Properties properties = new Properties();
InputStream inputStream = BaseDao.class.getClassLoader().getResourceAsStream("database.properties");
try {
properties.load(inputStream);
} catch (IOException e) {
throw new RuntimeException(e);
}
mysqlDriver = properties.getProperty("mysqlDriver");
mysqlUrl = properties.getProperty("mysqlUrl");
mysqlUser = properties.getProperty("mysqlUser");
mysqlPwd = properties.getProperty("mysqlPwd");
// System.out.println(mysqlDriver);
// System.out.println(mysqlUrl);
// System.out.println(mysqlUser);
// System.out.println(mysqlPwd);
}
将读取配置文件放入static代码块中，在BaseDao类加载的时候就会获取到资源文件中的资源
2.2、建立连接数据库提取方法
/**
* 建立connection链接
* @return Connection
*/
public Connection getConnection(){
Connection connection = null;
try {
Class.forName(mysqlDriver);
connection = DriverManager.getConnection(mysqlUrl, mysqlUser, mysqlPwd);
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
} catch (SQLException e) {
throw new RuntimeException(e);
}
return connection;
}
2.3、释放资源提取方法
/**
* 重载 释放资源
* @param resultSet 返回值
* @param preparedStatement Statement
* @param connection connection连接
*/
public void close(ResultSet resultSet, PreparedStatement preparedStatement, Connection connection){
try {
if (null!=resultSet)
resultSet.close();
if (null!=preparedStatement)
preparedStatement.close();
if (null!=connection)
connection.close();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
public void close(PreparedStatement preparedStatement,Connection connection){
this.close(null,preparedStatement,connection);
}
public void close(Connection connection){
this.close(null,connection);
}
此处使用了重载（方法名相同，参数列表不同，功能相似）
2.4、将增删改提取方法
/**
* 增删改
* @param sql sql语句
* @param params 传参
* @return 操作的条数
*/
public Integer executeUpdate(String sql, Object... params){
Integer num = -1;
Connection connection = this.getConnection();
PreparedStatement preparedStatement = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (null!=params) {
for (int i = 0; i < params.length; i++) {
preparedStatement.setObject(i+1,params[i]);
}
}
num = preparedStatement.executeUpdate();
} catch (SQLException e) {
throw new RuntimeException(e);
}finally {
this.close(preparedStatement,connection);
}
if (num>0){
System.out.println("操作成功");
}
return num;
}
- 此处使用了传不定值的参使用(Object… params)
- 调用此方法只需要将sql语句和参数就可操作数据
2.5、提取查询一条数据的方法
public T selectObjectById(RowMapper<T> row,String sql,Object... params){
Connection connection = this.getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
try {
preparedStatement = connection.prepareStatement(sql);
if (params!=null) {
for (int i = 0; i < params.length; i++) {
preparedStatement.setObject(i+1,params[i]);
}
}
resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
return row.mapper(resultSet);
}
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
this.close(resultSet,preparedStatement,connection);
}
return null;
}
- 这里用到了泛型（由于返回的值不能直接确定），传接口（将resultSet处理方法实现接口此处就可直接返回需要的值）
- 调用此方法将处理resultSet的lambda、sql语句和参数即可获取所需的数据
2.6、提取查询多条数据的方法
public List<T> selectObjectList(RowMapper<T> row, String sql, Object... params){
Connection connection = this.getConnection();
PreparedStatement preparedStatement = null;
ResultSet resultSet = null;
ArrayList<T> ts = new ArrayList<T>();
try {
preparedStatement = connection.prepareStatement(sql);
if (params!=null) {
for (int i = 0; i < params.length; i++) {
preparedStatement.setObject(i+1,params[i]);
}
}
resultSet = preparedStatement.executeQuery();
while (resultSet.next()) {
ts.add(row.mapper(resultSet));
}
return ts;
} catch (SQLException e) {
throw new RuntimeException(e);
} finally {
this.close(resultSet,preparedStatement,connection);
}
}
与查询一条类似，但是处理数据不同。
三、StudentDao接口
import org.example.demo.mysql.pojo.Student;
import java.util.List;
/**
* @program: jdbcMy
* @interfaceName StudentDao
* @description:
* @author: 太白
* @create: 2023-01-03 14:21
**/
public interface StudentDao {
Integer saveStudent(Student student);
Integer deleteStudent(String sid);
Integer updateStudent(Student student);
Student selectStudentById(String sid);
List<Student> selectStudentList();
}
四、RowMapper工具接口
package org.example.demo.mysql.utils;
import java.sql.ResultSet;
/**
* @program: jdbcMy
* @interfaceName RowMapper
* @description:
* @author: 太白
* @create: 2023-01-04 19:57
**/
public interface RowMapper<T> {
T mapper(ResultSet resultSet);
}
五、StudentDaoImpl实现类
package org.example.demo.mysql.dao2;
import org.example.demo.mysql.dao.StudentDao;
import org.example.demo.mysql.pojo.Student;
import org.example.demo.mysql.utils.RowMapper;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
/**
* @program: jdbcMy
* @interfaceName StudentDao2
* @description:
* @author: 太白
* @create: 2023-01-04 20:00
**/
public class StudentDao2Impl extends BaseDao2<Student> implements StudentDao {
// 增
public Integer saveStudent(Student student) {
String sql = "insert into student (sid,sname,sage,ssex) value (?,?,?,?)";
Integer integer = super.executeUpdate(sql,student.getSid(),student.getSname(),student.getSage(),student.getSsex());
return integer;
}
// 删
public Integer deleteStudent(String sid) {
String sql = "delete from student where sid = ?";
Integer integer = super.executeUpdate(sql,sid);
return integer;
}
// 改
public Integer updateStudent(Student student) {
String sql = "update student set sname=?,sage=?,ssex=? where sid=?";
Integer integer = super.executeUpdate(sql,student.getSname(),student.getSage(),student.getSsex(),student.getSid());
return integer;
}
// 查一条数据
public Student selectStudentById(String sid) {
String sql = "select sid,sname,sage,ssex from student where sid = ?";
Student student = super.selectObjectById(row, sql, sid);
return student;
}
// 实现处理result的接口方法（lambda表达式）
RowMapper<Student> row = new RowMapper<Student>() {
public Student mapper(ResultSet resultSet) {
Student student = new Student();
try {
student.setSid(resultSet.getString("sid"));
student.setSname(resultSet.getString("sname"));
student.setSage(resultSet.getDate("sage"));
student.setSsex(resultSet.getString("ssex"));
} catch (SQLException e) {
throw new RuntimeException(e);
}
return student;
}
};
// 查多条数据
public List<Student> selectStudentList() {
String sql = "select sid,sname,sage,ssex from student";
List<Student> students = super.selectObjectList(row, sql);
return students;
}
}
