JDBC的实现及注意事项
定义：JDBC(Java DataBase Connectivity):Java数据库连接。
工欲善其事必先利其器：
连接oracle数据库所需的包：https://pan.baidu.com/s/1HMUJYI2osnskp2aO-6qgbg
连接mysql数据库所需的包：https://pan.baidu.com/s/1ZVjOHeSfMs6KevQF7h4qKg
从实现功能即可的代码开始：
public class MyJdbc{
public static void main(String[] args) throws Exception{
//(1)加载驱动
//连接oracle oracle.jdbc.driver.OracleDriver
//连接mysql com.jdbc.mysql.dirver
Class.forName("oracle.jdbc.driver.OracleDriver");
//(2)建立数据库连接对象Connenction
Connection conn = DriverManager.getConnection(
"jdbc:oracle:thin:@127.0.0.1:1521:XE",
"liu",
"root");
//(3)创建Statement
String sql = "select * from emp";
PreparedStatement ps = conn.prepareStatement(sql);
//(4)通过statement的方法查询sql发往数据库，查询结果封装到resultset返回
ResultSet rs = ps.executeQuery();
while(rs.next()){
int empno = rs.getInt("empno");
String ename = rs.getString("ename");
String job = rs.getString("job");
Date hiredate = rs.getTimestamp("hiredate");
System.out.println(empno+"==>"+ename+"==>"+job+"==>"+hiredate);
}
//(5)关闭资源
rs.close();
ps.close();
conn.close();
}
}注意：
（1）mian函数里的异常未进行捕获，只是声名，如果出现异常则会直接中断程序，导致(5)可能不执行，资源得不到释放。
（2）在(3)中可以用PerpareStatement对象也可以使用Statement对象，推荐使用PerpareStatement对象，优点在于：
1.PerpareStatement类有预处理，效率高。
2.PerpareStatement类可以防止SQL注入。
（3）对(2)中DriverManager.getConnection(c1,c2,c3)中三个参数解释:
c1:jdbc:(oracle:thin/mysql):@ip:端口:数据库类型；
c2:数据库用户名；
c3:数据库密码。
（4)在(4)中语句 Date hiredate = rs.getTimestamp("hiredate")的Date hiredate 属于java.util包，而 rs.getTimestamp("hiredate")得到的Date数据属于java.sql包且是java.util包Date类的子类。
强化版JDBC连接代码：
创建如图所示的项目结构：
实体类代码：
public class Emp {
int empno;
String ename;
String job;
Date hiredate;
double sal;
int deptno;
public int getEmpno() {
return empno;
}
public void setEmpno(int empno) {
this.empno = empno;
}
public String getEname() {
return ename;
}
public void setEname(String ename) {
this.ename = ename;
}
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
public Date getHiredate() {
return hiredate;
}
public void setHiredate(Date hiredate) {
this.hiredate = hiredate;
}
public double getSal() {
return sal;
}
public void setSal(double sal) {
this.sal = sal;
}
public int getDeptno() {
return deptno;
}
public void setDeptno(int deptno) {
this.deptno = deptno;
}
}工具类代码：
public class DBLink {
public static Connection getconn(){
Connection conn = null;
try {
Class.forName("oracle.jdbc.driver.OracleDriver");
conn = DriverManager.getConnection(
"jdbc:oracle:thin:@127.0.0.1:1521:XE",
"liu",
"root");
}catch (Exception e){
e.printStackTrace();
}
return conn;
}
public static void closeconn(ResultSet r, PreparedStatement ps, Connection conn){
if(r != null){
try {
r.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(conn != null) {
try {
conn.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if(ps != null){
try {
ps.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void closeconn(PreparedStatement ps, Connection conn){
closeconn(null,ps,conn);
}
public static void main(String[] args) {
try {
System.out.println(getconn());
} catch (Exception e) {
e.printStackTrace();
}
}
}测试类代码：
public class EmpDao {
//根据姓名查找雇员信息
public static ArrayList sel(Emp e){
Connection conn = DBLink.getconn();
PreparedStatement ps = null;
ResultSet rs = null;
ArrayList arr = new ArrayList<>();
String sql = "select * from emp where ename = ?";
try {
ps = conn.prepareStatement(sql);
ps.setString(1,e.getEname());
rs = ps.executeQuery();
while (rs.next()){
Emp emp = new Emp();
int empno = rs.getInt("empno");
String ename = rs.getString("ename");
String job = rs.getString("job");
Date hiredate = rs.getTimestamp("hiredate");
double sal = rs.getDouble("sal");
int deptno = rs.getInt("deptno");
emp.setEmpno(empno);
emp.setEname(ename);
emp.setJob(job);
emp.setHiredate(hiredate);
emp.setSal(sal);
emp.setDeptno(deptno);
arr.add(emp);
}
} catch (SQLException e1) {
e1.printStackTrace();
}finally {
DBLink.closeconn(rs,ps,conn);
return arr;
}
}
//插入一条信息
public static void in(Emp e){
Connection conn = DBLink.getconn();
PreparedStatement ps =null;
String sql = "insert into emp(empno,ename,job,hiredate,sal,deptno) values(?,?,?,?,?,?) ";
try {
ps = conn.prepareStatement(sql);
ps.setInt(1,e.getEmpno());
ps.setString(2,e.getEname());
ps.setString(3,e.getJob());
long t =e.getHiredate().getTime();
Timestamp timestamp = new Timestamp(t);
ps.setObject(4,timestamp);
ps.setDouble(5,e.getSal());
ps.setInt(6,e.getDeptno());
ps.executeUpdate();
} catch (SQLException e1) {
e1.printStackTrace();
}finally {
DBLink.closeconn(ps,conn);
}
}
public static void main(String[] args) {
/*查找
Emp e = new Emp();
e.setEname("JONES");
ArrayList arr = sel(e);
for (Emp emp : arr) {
System.out.println(emp.getEmpno()+"\t"+emp.getEname()+"\t"+emp.getJob()+"\t"+emp.getHiredate()
+"\t"+emp.getSal()+"\t"+emp.getDeptno());
}
*/
//插入
Date date = new Date();
Emp e = new Emp();
e.setEmpno(9527);
e.setEname("周星星");
e.setJob("CLERK");
e.setHiredate(date);
e.setSal(1520);
e.setDeptno(20);
in(e);
}
}