JDBC使用方法
JDBC
1. JDBC基本步骤
- 加载驱动（选择数据库）
- 获取连接（与数据库建立连接）
- 准备sql
- 封装处理块
- 发送执行sql语句，得到结果集
- 处理结果
- 关闭
配置文件代码：
classpath=oracle.jdbc.driver.OracleDriver
url=jdbc:oracle:thin:@localhost:1521:XE
user=SCOTT
pwd=TIGER
工具类代码：
import java.io.IOException;
import java.sql.*;
import java.util.Properties;
//查询emp表中的所有数据，并将结果打印至控制台
public class JDBCDemo01 {
public static void main(String[] args) throws ClassNotFoundException, SQLException, IOException {
Properties pro = new Properties();
pro.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("JDBCpath.properties"));
//加载驱动（选择数据库）
Class.forName(pro.getProperty("classpath"));
//获取连接
Connection conn = DriverManager.getConnection(pro.getProperty("url"),pro.getProperty("user"),pro.getProperty("pwd"));
//准备sql
String sql = "select * from emp";
//封装静态处理块
Statement statement = conn.createStatement();
//执行sql，得到结果集
ResultSet result = statement.executeQuery(sql);
//处理结果
while (result.next()){
int empno = result.getInt(1);
String ename = result.getString("ename");
String job = result.getString(3);
int mgr = result.getInt("mgr");
Date hiredate = result.getDate("hiredate");
int sal = result.getInt(6);
int comm = result.getInt(7);
int deptno = result.getInt("deptno");
System.out.println(empno+"->"+ename+"->"+job+"->"+mgr+"->"+hiredate+"->"+sal+"->"+comm+"->"+deptno);
}
conn.close();
}
}
封装工具类，后面使用，代码如下：
//封装工具类
import java.io.IOException;
import java.sql.*;
import java.util.Properties;
public class JDBCUtils {
private static Properties pro = new Properties();
static {
try {
pro.load(Thread.currentThread().getContextClassLoader().getResourceAsStream("JDBCpath.properties"));
} catch (IOException e) {
e.printStackTrace();
}
try {
Class.forName(pro.getProperty("classpath"));
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
//获取连接
public static Connection getConnection() throws SQLException {
Connection conn = DriverManager.getConnection(pro.getProperty("url"),pro.getProperty("user"),pro.getProperty("pwd"));
return conn;
}
//关闭
public static void close(Connection conn, PreparedStatement ps, ResultSet result){
if (conn!=null){
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (ps!=null){
try {
ps.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (result!=null){
try {
result.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
//关闭的重载方法
public static void close(Connection conn, PreparedStatement ps){
if (conn!=null){
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (ps!=null){
try {
ps.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
//关闭的重载方法
public static void close(Connection conn, PreparedStatement ps1,PreparedStatement ps2){
if (conn!=null){
try {
conn.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (ps1!=null){
try {
ps1.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
if (ps2!=null){
try {
ps2.close();
} catch (SQLException throwables) {
throwables.printStackTrace();
}
}
}
}
2. JDBC中的预处理块及手动提交事务
- JDBC中事务默认自动提交
- SQL注入的问题，SQL注入即恶意的把传输到后台的数据进行拼接，或者前台用户输入的内容不符合正常情况，造成数据的不安全。使用静态处理块会遇到该问题，因为SQL语句是由字符串拼接成功的。解决这种情况需要使用预处理块，预处理块会预先编译，提高效率，预防SQL注入问题的发生
由于JDBC中事务是自动提交的，有时会出现数据的不安全情况，例如一个人转账给另一个人，会出现钱转出对方未收到的情况，钱也就不见了。
代码：
//zhangsan转账1000给lisi
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.SQLException;
public class JDBCDemo02 {
public static void main(String[] args) {
Connection conn = null;
PreparedStatement ps1 = null;
PreparedStatement ps2 = null;
try {
//获取连接
conn = JDBCUtils.getConnection();
//设置手动提交事务
conn.setAutoCommit(false);
//准备sql
String sql1 = "update test_commit set account=account-1000 where uname='zhangsan'";
String sql2 = "update test_commit set account=account+1000 where uname='lisi'";
ps1 = conn.prepareStatement(sql1);
ps2 = conn.prepareStatement(sql2);
int num1 = ps1.executeUpdate();
int num2 = ps2.executeUpdate();
if (num1>0&&num2>0){
conn.commit();
System.out.println("转账成功");
}else {
conn.rollback();
System.out.println("转账失败");
}
} catch (SQLException throwables) {
throwables.printStackTrace();
} finally {
//关闭
JDBCUtils.close(conn,ps1,ps2);
}
}
}
3. 使用JDBC实现对用户的基本操作
注：在Oracle数据库中的字符串类型对应java中的String类型，number类型对应java中的java.math.BigDecimal类型。当number转为java中的BigDecimal类型时，与javabean中的属性类型不一致时有两种解决方案。
- 将属性的类型变为BigDecimal类型
- 将数据转为对应的基本数据类型，再赋值给对应类型的属性
封装工具类，增删改为一个方法，查询为一个方法，代码：
//定义工具类
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.math.BigDecimal;
import java.sql.*;
import java.util.ArrayList;
import java.util.List;
public class BaseDao<T> {
//增删改功能
public static boolean modify(String sql,Object ... arr){
boolean flag = false;
Connection conn = null;
PreparedStatement ps = null;
try {
//获取连接
conn = JDBCUtils.getConnection();
conn.setAutoCommit(false);
//创建预处理块
ps = conn.prepareStatement(sql);
//给sql语句中的?赋值
if(arr!=null && arr.length>0){
for(int i=0;i<=arr.length-1;i++){
ps.setObject(i+1,arr[i]);
}
}
//执行
int num = ps.executeUpdate();
if (num>0){
flag = true;
conn.commit();
}else {
conn.rollback();
}
} catch (SQLException throwables) {
throwables.printStackTrace();
}finally {
JDBCUtils.close(conn,ps);
}
return flag;
}
//查询功能
public List<T> search(String sql, Class<T> cls, Object ... arr){
//存储查询数据的集合
List<T> list = new ArrayList<>();
Connection conn = null;
PreparedStatement ps = null;
ResultSet result = null;
ResultSetMetaData metaData = null;
try {
//获取连接
conn = JDBCUtils.getConnection();
//创建预处理块
ps = conn.prepareStatement(sql);
//给sql语句中的？赋值
if(arr!=null && arr.length>0){
for(int i=0;i<=arr.length-1;i++){
ps.setObject(i+1,arr[i]);
}
}
//执行
result = ps.executeQuery();
//结果集
metaData = result.getMetaData();
//结果集中字段个数
int count = metaData.getColumnCount();
//对结果集进行处理
while (result.next()) {
//创建对应类型的对象
T obj = cls.getConstructor().newInstance();
//遍历结果集中的每一个字段,获取值,获取javabean类中对应这个字段的属性,为当前属性赋值
for (int i = 1; i <= count; i++) {
//获取值
Object value = result.getObject(i);
if ("java.math.BigDecimal".equals(value.getClass().getName())) {
value = ((BigDecimal) value).intValue();
}
//获取属性名
String fieldName = metaData.getColumnLabel(i);
//获取javabean的属性
Field field = cls.getDeclaredField(fieldName);
//私有属性设置访问权限
field.setAccessible(true);
//赋值
field.set(obj, value);
//关闭访问权限
field.setAccessible(false);
}
//将对象放入集合
list.add(obj);
}
} catch (SQLException throwables) {
throwables.printStackTrace();
} catch (InstantiationException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (NoSuchFieldException e) {
e.printStackTrace();
}finally {
JDBCUtils.close(conn,ps,result);
}
return list;
}
}
自定义类：
import java.io.Serializable;
import java.util.Date;
import java.util.Objects;
public class Employee implements Serializable {
private Integer empno;
private String ename;
private String job;
private Integer mgr;
private Date hiredate;
private Integer sal;
private Integer comm;
private Integer deptno;
public Employee() {
}
public Employee(Integer empno, String ename, String job, Integer mgr, Date hiredate, Integer sal, Integer comm, Integer deptno) {
this.empno = empno;
this.ename = ename;
this.job = job;
this.mgr = mgr;
this.hiredate = hiredate;
this.sal = sal;
this.comm = comm;
this.deptno = deptno;
}
public Integer getEmpno() {
return empno;
}
public void setEmpno(Integer 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 Integer getMgr() {
return mgr;
}
public void setMgr(Integer mgr) {
this.mgr = mgr;
}
public Date getHiredate() {
return hiredate;
}
public void setHiredate(Date hiredate) {
this.hiredate = hiredate;
}
public Integer getSal() {
return sal;
}
public void setSal(Integer sal) {
this.sal = sal;
}
public Integer getComm() {
return comm;
}
public void setComm(Integer comm) {
this.comm = comm;
}
public Integer getDeptno() {
return deptno;
}
public void setDeptno(Integer deptno) {
this.deptno = deptno;
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Employee employee = (Employee) o;
return Objects.equals(empno, employee.empno) &&
Objects.equals(ename, employee.ename) &&
Objects.equals(job, employee.job) &&
Objects.equals(mgr, employee.mgr) &&
Objects.equals(hiredate, employee.hiredate) &&
Objects.equals(sal, employee.sal) &&
Objects.equals(comm, employee.comm) &&
Objects.equals(deptno, employee.deptno);
}
@Override
public int hashCode() {
return Objects.hash(empno, ename, job, mgr, hiredate, sal, comm, deptno);
}
@Override
public String toString() {
return "Employee{" +
"empno=" + empno +
", ename='" + ename + '\'' +
", job='" + job + '\'' +
", mgr=" + mgr +
", hiredate=" + hiredate +
", sal=" + sal +
", comm=" + comm +
", deptno=" + deptno +
'}';
}
}
测试代码：
import java.util.List;
public class UserDemo03 {
public static void main(String[] args) {
//测试增删改功能
System.out.println(BaseDao.modify("insert into test_user values(?,?)","zhangsan","10086"));
System.out.println(BaseDao.modify("insert into test_user values(?,?)","lisi","10087"));
System.out.println(BaseDao.modify("insert into test_user values(?,?)","wangwu","10088"));
System.out.println(BaseDao.modify("delete from test_user where uname=?","wangwu"));
System.out.println(BaseDao.modify("update test_user set pwd=? where uname=?","22222","lisi"));
//测试查询方法
BaseDao<Employee> bd = new BaseDao<>();
List<Employee> list = bd.search("select empno \"empno\",ename \"ename\" from emp where empno in (?,?) ",Employee.class,7369,7499);
list.forEach(System.out::println);
}
}