JDBC练习-select语句
定义一个方法，查询emp表中的数据将其封装为对象，然后装载集合，然后打印
1.定义emp类
2.定义方法public List<Emp> findAll(){}
3.实现方法select * from emp;
Emp类
public class Emp {
private int id;
private String ename;
private int job_id;
private int mgr;
private Date joindate;
private double salary;
private double bonus;
private int dept_id;
//toString
@Override
public String toString() {
return "Emp{" +
"id=" + id +
", ename='" + ename + '\'' +
", job_id=" + job_id +
", mgr=" + mgr +
", joindate=" + joindate +
", salary=" + salary +
", bonus=" + bonus +
", dept_id=" + dept_id +
'}';
}
//get和set
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public int getJob_id() {
return job_id;
}
public void setJob_id(int job_id) {
this.job_id = job_id;
}
public int getMgr() {
return mgr;
}
public void setMgr(int mgr) {
this.mgr = mgr;
}
public Date getJoindate() {
return joindate;
}
public void setJoindate(Date joindate) {
this.joindate = joindate;
}
public double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
public double getBonus() {
return bonus;
}
public void setBonus(double bonus) {
this.bonus = bonus;
}
public int getDept_id() {
return dept_id;
}
public void setDept_id(int dept_id) {
this.dept_id = dept_id;
}
测试类：
public static void main(String[] args) {
List<Emp> all = new JdbcPractice6().findAll();
for (Emp emp : all) {
System.out.println(emp);
}
}
/**
* 查询所有emp对象
* @return
*/
public List<Emp> findAll(){
Connection conn = null;
Statement state = null;
ResultSet rs =null;
List<Emp> list = null;
try {
//1.注册驱动
Class.forName("com.mysql.cj.jdbc.Driver");
//2.获取连接
conn = DriverManager.getConnection("jdbc:mysql:///db2", "root", "root");
//3.定义sql
String sql = "select * from emp";
//4.获取执行sql对象
state = conn.createStatement();
//5.执行sql(结果集对象)
rs = state.executeQuery(sql);
//6.遍历结果集,封装对象,装载集合
Emp emp= null;
list = new ArrayList<>();
while (rs.next()){
//6.1获取数据
int id = rs.getInt("id");
String ename = rs.getString("ename");
int job_id = rs.getInt("job_id");
int mgr = rs.getInt("mgr");
Date joindate = rs.getDate("joindate");
double salary = rs.getDouble("salary");
double bonus = rs.getDouble("bonus");
int dept_id = rs.getInt("dept_id");
//创建emp对象,并赋值
emp = new Emp();
emp.setId(id);
emp.setEname(ename);
emp.setJob_id(job_id);
emp.setMgr(mgr);
emp.setJoindate(joindate);
emp.setSalary(salary);
emp.setBonus(bonus);
emp.setDept_id(dept_id);
//装载集合
list.add(emp);
}
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
} catch (SQLException e) {
throw new RuntimeException(e);
}finally {
if (rs != null){
try {
rs.close();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
if (state != null){
try {
state.close();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
throw new RuntimeException(e);
}
}
}
return list;
}
JDBC工具类
抽取工具类：JDBCUtils
目的：简化书写
分析：
1.注册驱动
2.抽取一个方法获取连接对象
需求：不想传递参数（麻烦），还得保证工具类的通用性。
解决：配置文件
jdbc.properties
url =
user =
password =
3.抽取一个方法释放资源
JDBCUtils工具类
/**
* JDBC工具类
*
*/
public class JDBCUtils {
//声明三个成员变量
private static String url;// 连接数据库
private static String user;// 用户名
private static String password;// 密码
private static String driver;// 连接驱动
/**
* 文件的读取，只需要读取一次即可拿到这些值，使用静态代码块(工具类静态块)
*/
static {
//读取资源文件，获取值
try {
//1.创建Properties集合类
Properties prop = new Properties();
//2.加载文件
prop.load(new FileReader("src/main/resources/jdbc.properties"));
//3.获取数据,赋值(于配置文件中的属性名要一致)
url = prop.getProperty("url");
user = prop.getProperty("user");
password = prop.getProperty("password");
driver = prop.getProperty("driver");
//注册驱动
Class.forName(driver);
} catch (IOException e) {
throw new RuntimeException(e);
} catch (ClassNotFoundException e) {
throw new RuntimeException(e);
}
}
/**
* 获取连接
* @return 连接对象
*/
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url, user, password);
}
/**
* 释放资源
* @param stmt
* @param conn
*/
public static void close(ResultSet rs, Statement stmt, Connection conn){
if (rs != null){
try {
rs.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (stmt != null){
try {
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (conn != null){
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
测试类
public static void main(String[] args) {
//创建方法引用方法
List<Emp> all = new JdbcPractice7().findAll2();
for (Emp emp : all) {
System.out.println(emp);
}
}
/**
* 查询所有emp对象
* @return
*/
public List<Emp> findAll2(){
Connection conn = null;
Statement state = null;
ResultSet rs =null;
List<Emp> list = null;
try {
// //1.注册驱动
// Class.forName("com.mysql.cj.jdbc.Driver");
// //2.获取连接
// conn = DriverManager.getConnection("jdbc:mysql:///db2", "root", "root");
conn = JDBCUtils.getConnection();
//3.定义sql
String sql = "select * from emp";
//4.获取执行sql对象
state = conn.createStatement();
//5.执行sql(结果集对象)
rs = state.executeQuery(sql);
//6.遍历结果集,封装对象,装载集合
Emp emp= null;
list = new ArrayList<>();
while (rs.next()){
//6.1获取数据
int id = rs.getInt("id");
String ename = rs.getString("ename");
int job_id = rs.getInt("job_id");
int mgr = rs.getInt("mgr");
Date joindate = rs.getDate("joindate");
double salary = rs.getDouble("salary");
double bonus = rs.getDouble("bonus");
int dept_id = rs.getInt("dept_id");
//创建emp对象,并赋值
emp = new Emp();
emp.setId(id);
emp.setEname(ename);
emp.setJob_id(job_id);
emp.setMgr(mgr);
emp.setJoindate(joindate);
emp.setSalary(salary);
emp.setBonus(bonus);
emp.setDept_id(dept_id);
//装载集合
list.add(emp);
}
} catch (SQLException e) {
throw new RuntimeException(e);
}finally {
//释放资源
JDBCUtils.close(rs, state, conn);
}
return list;
}
标签：语句,JDBC,rs,int,public,emp,new,id,select From： https://www.cnblogs.com/qihaokuan/p/16812991.html