JAVA企业面试题精选 JDBC 1-10
2.JDBC
2.1.Java数据库编程包含哪些类和接口?Java数据库编程的基本过程是什么?
参考答案:
题目中各问题的答案如下:
1.Java数据库编程包含Connection,ResultSet,PreparedStatement,Statement,DriverManager.
2.Java中访问数据库的步骤如下:
1)注册驱动程序;
2)建立连接;
3)创建Statement;
4)执行SQL语句;
5)处理结果集(若SQL语句为查询语句);
6)关闭连接.
2.2.Statement,PreparedStatement,CallableStatement的区别?
参考答案:
&esmp; Statement,PreparedStatement,CallableStatement的区别有以下几点:
&esmp; 1.Statement是PreparedStatement和CallableStatement的父类;
&esmp; 2.Statement是直接发送SQL语句到数据库,事先没有进行预编译.PreparedStatement会将SQL进行预编译,当SQL语句要重复执行时,数据库会调用以前预编译好的SQL语句,所以PreparedStatement在性能方面会更好;
&esmp; 3.PreparedStatement在执行SQL时,对传入的参数可以进行强制的类型转换.以保证数据格式与底层的数据库格式一致;
&esmp; 4.CallableStatement适用于执行存储过程.
2.3Java中如何进行事务的处理?
参考答案:
Connection类中提供了3个事务处理方法:
setAutoCommit(Boolean autoCommit):设置是否自动提交事务,默认为自动提交,即为true,通过设置false禁止自动提交事务;
commit():提交事务;
rollback():回滚事务.
2.4下述程序是一段简单的基于JDBC的数据库访问代码,实现了以下功能:从数据库中查询product表中的所有记录,然后打印输出到控制台.该代码质量较低,如没有正确处理异常,连接字符串以”魔数”的形式直接存在于代码中等,请用你的思路重新编写程序,完成相同的功能,提高代码质量.
public void printProducts(){
Connection c = null;
Statements s = null;
ResultSet r = null;
try{
c=DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:sid","username","password");
s=c.createStatement();
r=s.executeQuery("select id, name, price from product");
System.out.println("Id\tName\tPrice");
while(r.next()){
int x = r.getInt("id");
String y = r.getString("name");
float z = r.getFloat("price");
System.out.println(x + "\t" + y + "\t" + z);
}
} catch(Exception e){
}
}参考答案:
程序改造一:
SQLException一般情况下无法恢复.通常情况下,数据库访问代码在捕获该异常后,在catch块中进行一些必要的处理(例如事务回滚)后,将其直接抛出;或者封装成自定义异常的形式抛出.使用格式如下:
try{
//JDBC访问
return ...;
} catch (SQLException e){
//异常处理
throw new DAOException("访问数据库错误",e);
} finally {
//关闭连接
}其中DAOException是自定义的异常.
程序改造二:
定义常量类Constant,把连接数据库的信息,定义成常量后再使用.
改造后的程序代码如下所示:
class Constant{
public static final String URL="jdbc:oracle:thin:@127.0.0.1:1521:sid";
public static final String USERNAME="username";
public static final String PASSWORD="password";
}
class DAOException extends Exception{
public DAOException(){
super();
}
public DAOException(String msg){
super(msg);
}
}
public class Test{
public void printProducts() throws DAOException{
Connection c = null;
Statement s = null;
ResultSet r = null;
try{
c = DriverManager.getConnection(Constant.URL,Constant.USERNAME,Constant.PASSWORD);
s = c.createStatement();
r = s.executeQuery("select id,name,price from product");
System.out.println("Id\tName\tPrice");
while(r.next()){
int x = r.getInt("id");
String y = r.getString("name");
float z = r.getFloat("price");
System.out.println(x + "\t" + y + "\t" + z);
}
} catch (SQLException e){
throw new DAOException("数据库异常");
} finally {
try{
r.close();
s.close();
c.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}2.5.请根据以下要求来完成题目:
会议室预定模块.某公司有多个会议室,以房间号区分.如果某部门需要预定会议室,则会提交预定请求(包含预定开始使用时间,预定结束使用,所预定会议室房间号).
1.设计一个表,保存会议室预定信息.
2.要求采用SQL语句及Java代码段判断在2003-3-10下午3:00~4:00 3号会议室是否空闲.
参考答案:
在Oracle数据库中创建会议表及插入测试数据的SQL语句:
CREATE TABLE MEETING(
ID NUMBER PRIMARY KEY,
ROOM_ID VARCHAR2(10),
ISUSED CHAR,
BEGIN TIMESTAMP,
END TIMESTAMP
);
INSERT INTO MEETING VALUES(1,'201',1,TO_DATE('2003-03-10 15:00:00','YYYY-MM-DD HH24:MI:SS'),TO_DATE('2003-3-10 16:00:00','YYYY-MM-DD HH24:MI:SS'));
INSERT INTO MEETING VALUES(2,'201',1,TO_DATE('2003-03-10 17:00:00','YYYY-MM-DD HH24:MI:SS'),TO_DATE('2003-3-10 22:00:00','YYYY-MM-DD HH24:MI:SS'));使用Java代码判断在2003-3-10下午3:00~4:00 3号会议室是否空闲的代码如下所示:
package com.welkin;
import java.sql.*;
pulbic class Test{
public static void main(String[] args){
String driverName = "oracle.jdbc.OracleDriver";
String url = "jdbc:oracle.thin:@127.0.0.1:1521:orcl";
String username = "welkin";
String pwd = "123456";
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
try{
Class.forName(driverName);
con = DriverManager.getConnection(url, username, pwd);
stmt = con.createStatement();
String sql = "select isUsed from " +
"meeting " +
"where ((begin between to_date('2003-03-10 15:00:00'," + "'yyyy-mm-dd hh24:mi:ss') and to_date('2003-03-10 16:00:00'," + "'yyyy-mm-dd hh24:mi:ss'))" +
"or(end between to_date('2003-03-10 15:00:00'," + "'yyyy-mm-dd hh24:mi:ss') and to_date('2003-03-10 16:00:00'," + "'yyyy-mm-dd hh24:mi:ss')))" +
" and room_id=201";
if(stmt.execute(sql)){
rs = stmt.getResultSet();
}
StringBuffer sb = new StringBuffer("isFree:");
while(rs.next()){
sb.append(rs.getInt(1) + " ");
}
System.out.println(sb.toString());
} catch (Exception e) {
e.printStackTrace();
} finally {
try{
rs.close();
stmt.close();
con.close();
} catch (Exception e1){
e1.printStackTrace();
}
}
}
}2.6.假设有以下数据,请分别用XML和JSON表述以下数据.请写一个实体类来定义以下数据类型
表数据(person)
| 公司 | 部门 | 名字 | 性别 | 年龄 | 生日 |
|---|---|---|---|---|---|
| 中国石油 | 技术部 | 张三 | 男 | 30 | 1983-4-1 |
| 中国石油 | 销售部 | 李四 | 女 | 30 | 1983-4-2 |
| 中国电信 | 技术部 | 王五 | 男 | 25 | 1988-1-2 |
| 中国电信 | 人事部 | jack | 男 | 30 | 1983-4-3 |
参考答案:
上述数据使用JSON的形式表述如下:
{"persons":[
{"公司":"中国石油","部门":"技术部","名字":"张三","性别":"男","年龄":"30","生日":"1983-4-1"},
{"公司":"中国石油","部门":"销售部","名字":"李四","性别":"女","年龄":"30","生日":"1983-4-2"},
{"公司":"中国电信","部门":"技术部","名字":"王五","性别":"男","年龄":"25","生日":"1988-1-2"},
{"公司":"中国电信","部门":"人事部","名字":"jack","性别":"男","年龄":"30","生日":"1983-4-3"}
]}上述数据使用XML表述形式:
<persons>
<person>
<公司>中国石油公司>
<部门>技术部部门>
<名字>张三名字>
<性别>男性别>
<年龄>30年龄>
<生日>1983-4-1生日>
person>
<person>
<公司>中国石油公司>
<部门>销售部部门>
<名字>李四名字>
<性别>女性别>
<年龄>30年龄>
<生日>1983-4-2生日>
person>
<person>
<公司>中国电信公司>
<部门>技术部部门>
<名字>王五名字>
<性别>男性别>
<年龄>25年龄>
<生日>1988-1-2生日>
person>
<person>
<公司>中国电信公司>
<部门>人事部部门>
<名字>jack名字>
<性别>男性别>
<年龄>30年龄>
<生日>1983-4-3生日>
person>
persons>使用实体类定义如下:
public class Person{
private String company;
private String dept;
private String name;
private String gender;
private int age;
private String birthday;
public String getCompany(){
return company;
}
public void setCompany(String company){
this.company = company;
}
public String getDept(){
return dept;
}
public void setDept(String dept){
this.dept = dept;
}
public String getName(){
return name;
}
public void setName(String name){
this.name = name;
}
public String getGender(){
return gender;
}
public void setGender(String gender){
this.gender = gender;
}
public int getAge(){
return age;
}
public void setAge(int age){
this.age = age;
}
public String getBirthday(){
return birthday;
}
public void setBirthday(String birthday){
this.birthday = birthday;
}
}2.7.使用Java语言写一个连接Oracle数据库的程序,能够完成修改和查询工作
参考答案:
使用JDBC连接Oracle数据库,并完成修改和查询功能的代码如下:
1.创建数据库表SERVICE_DETAIL,SQL语句如下所示:
CREATE TABLE SERVICE_DETAIL(
ID NUMBER(11) CONSTRAINT SERVICE DETAIL ID PK PRIMARY KEY,
SERVICE_ID NUMBER(11),
HOST VARCHAR2(15),
USER_NAME VARCHAR2(50),
PID NUMBER(11),
LOGIN_TIME DATE,
LOGOUT_TIME DATE,
DURATION NUMBER(20,9),
COST NUMBER(20,6)
);2.db.properties文件包含连接数据库的信息
jdbc.driver=oracle.jdbc.OracleDriver
jdbc.url=jdbc:oracle:thin:@127.0.0.1:1521:ORCL
jdbc.user=welkin
jdbc.password=1234563.BaseDAO类包含打开和关闭连接的方法
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.util.Properties;
public class BaseDAO{
private static Properties properties = new Properties();
private static String driver = properties.getPropety("jdbc.driver");
private static String url = properties.getProperty("jdbc.url");
private static String user = properties.getProperty("jdbc.user");
private static String pwd = properties.getProperty("jdbc.password");
static{
try{
//加载配置文件
properties.load(BaseDAO.class.getClassLoader().getResourceAsStream("com/welkin/test/daodemo/db.properties");
driver = properties.getProperty("jdbc.driver");
url = properties.getProperty("jdbc.url");
user = properties.getProperty("jdbc.user");
pwd = properties.getProperty("jdbc.password");
Class.forName(driver);
} catch (Exception e) {
e.printStackTrace();
throw new RuntimeException(e);
}
}
protected static Connection openConnection() throws SQLException{
return DriverManager.getConnection(url, user, pwd);
}
protected static void closeConnection(Connection con){
if(con != null){
try{
con.close();
} catch (SQLException e){
}
}
}
}4.ServiceDetail类是数据库表和Java类的映射
import java.io.Serializable;
import java.math.BigDecimal;
import java.util.Date;
public class ServiceDetail implements Serializable{
private static final long serialVersionUID = 1L;
private Integer id;
private Integer serviceid;
private String host;
private String userName;
private Integer pid;
private Date loginTime;
private Date logoutTime;
private Integer duration;
private BigDecimal cost;
public ServiceDetail(){
}
public Integer getId(){
return id;
}
public void setId(Integer id){
this.id = id;
}
public Integer getServiceid(){
return serviceid;
}
public void setServiceid(Integer serviceid){
this.serviceid = serviceid;
}
public String getHost(){
return host;
}
public void setHost(String host){
this.host = host;
}
public String getUserName(){
return userName;
}
public void setUserName(){
this.userName = userName;
}
public Integer getPid(){
return pid;
}
public void setPid(Integer pid){
this.pid = pid;
}
public Date getLoginTime(){
return loginTime;
}
public void setLoginTime(Date loginTime){
this.loginTime = loginTime;
}
public Date getLogoutTime(){
return logoutTime;
}
public void setLogoutTime(Date logoutTime){
this.logoutTime = logoutTime;
}
public Integer getDuration(){
return durantion;
}
public void setDuration(Integer duration){
this.duration = duration;
}
public BigDecimal getCost(){
return cost;
}
public void setCost(BigDecimal cost){
this.cost = cost;
}
@Override
public String toString(){
return "ServiceDetail [id=" + id + ", serviceid=" + serviceid
+ ", host" + host + ", userName=" + userName + ", pid=" + pid
+ ", loginTime=" + loginTime + ", logoutTime=" + logoutTime
+ ", durantion=" + duration + ", cost=" + cost + "]";
}
} 5.实现对ServiceDetail表的更新和查询.
import java.sql.Connection;
import java.sql.Date;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.List;
import com.welkin.test.daodemo.entity.ServiceDetail;
public class ServiceDetailDAO extends BaseDAO{
private static final String UPDATE = "update SERVICE_DETAIL set "
+ "SERVICE_ID=?, HOST=?, USER_NAME=?, PID=?, LOGIN_TIME=?, "
+ "LOGOUT_TIME=?, DURATION=?, COST=? where ID=?";
priavte static final String FIND_ALL="select ID, SERVICE_ID, HOST, USER_NAME, PID,"
+ "LOGIN_TIME, LOGOUT_TIME, DURATION, COST from SERVICE_DETAIL";
public List findAll(){
Connection con = null;
PreparedStatement stmt = null;
try{
con = openConnection();
stmt = com.prepareStatement(FIND_ALL);
ResultSet rs = stmt.executeQuery();
List list = new ArrayList();
while(rs.next()){
list.add(toServiceDetail(rs));
}
rs.close();
stmt.close();
return list;
} catch (SQLException e) {
System.out.println("数据库访问异常!");
throw new RuntimeException(e);
} finally {
closeConnection(con);
}
}
public void update(ServiceDetail serviceDetail){
Connection con = null;
PreparedStatement stmt = null;
try{
con = openConnection();
stmt = con.prepareStatement(UPDATE);
stmt.setInt(1,serviceDetail.getServiceid());
stmt.setString(2,serviceDetail.getHost());
stmt.setString(3,serviceDetail.getUserName());
stmt.setInt(4,serviceDetail.getPid());
stmt.setDate(5,new Date(serviceDetail.getLoginTime().getTime());
stmt.setDate(6,Date(serviceDetail.getLogoutTime().getTime()));
stmt.setTimestamp(5,new Timestamp(serviceDetail.getLoginTime().getTime()));
stmt.setTimestamp(6,Timestamp(serviceDetail.getLogoutTime().getTime()));
stmt.setInt(7, serviceDetail.getDuration());
stmt.setBigDecimal(8,serviceDetail.getCost());
stmt.setInt(9,serviceDetail.getId());
stmt.executeUpdate();
stmt.close();
} catch (SQLException e) {
System.out.println("数据库访问异常!");
throw new RuntimeException(e);
}
}
private ServiceDetail toServiceDetail(ResultSet rs) throws SQLException{
ServiceDetail serviceDetail = new ServiceDetail();
serviceDetail.setId(rs.getInt("ID"));
serviceDetail.setServiceid(rs.getInt("SERVICE_ID"));
serviceDetail.setHost(rs.geString("HOST"));
serviceDetail.setUserName(rs.getString("USER_NAME"));
serviceDetail.setPid(rs.getInt("PID");
serviceDetail.setLoginTime(rs.getTimestamp("LOGIN_TIME"));
serviceDetail.setLogoutTime(rs.getTimestamp("LOGOUT_TIME"));
serviceDetail.setDuration(rs.getInt("DURATION"));
serviceDetail.setCost(rs.getBigDecimal("COST"));
return serviceDetail;
}
} 2.8.以下数据库操作的程序片段如何改进会更好
try{
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/test","root","123456");
Statement stmt = conn.createStatement();
String sql = "select * from T_User where username='" + name + "' and password='" + password + "'";
ResultSet rs = stmt.executeQuery(sql);
if(rs.next()){
System.out.println("User Name and Password is correct!");
} else {
System.out.println("User Name and Password pair is invalidate");
}
} catch (Exception e){
e.printStackTrace();
}参考答案:
使用PreparedStatement防止SQL注入,改进的代码如下所示:
try{
Class.forName("com.mysql.jdbc.Driver");
Connection conn = DriverManager.getConnection("jdbc:mysql://localhost/test","root","123456");
String sql = "select count(*) from t_user where username=? and password=?";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1,username);
ps.setString(2,password);
Resultset rs = ps.executeQuery();
rs.next();
int count = rs.getInt(1);
if(count == 1){
System.out.println("User Name and Password is correct!");
} else {
System.out.println("User Name and Password pair is invalidate");
}
} catch (Exception e){
e.printStackTrace();
}2.9.写出一段JDBC连接本机MySQL数据库的代码
参考答案:
Class.forName("com.mysql.jdbc.Driver");
String url="jdbc:mysql://localhost/test";
Stirng user='root';
String password='root';
Connection conn = DriverManager.getConnection(url,user,password);2.10.利用Java IO流编写一个SQL语句执行工具,功能类似于(Oracle sqlplus)
例如:输入select * from t_user按回车,可以显示如下结果:
id name age gender
1 张三 20 男
2 李四 21 女
输入insert into t_user(id,name,age,gender)values(1,’王五’,20,’男’)按回车,控制台显示结果:已增加一条记录.
参考答案:
public class Q010{
public static void main(String args[]){
Scanner in = new Scanner(System.in);
String sql = in.nextLine();
sql = sql.trim();
System.out.println(sql);
Connection con = Q010.getConnection();
PreparedStatement pst = con.prepareStatement(sql);
if(sql.startWith("select"){
ResultSet rs = pst.executeQuery();
System.out.println("id name age gender");
System.out.println("-------------------");
while(rs.next()){
System.out.println(rs.getString("id" + " " + rs.getString("name") + " "
+ rs.getString("age") + " " + rs.getString("gender"));
}
} else if(sql.startWith("insert"){
pst.executeUpdate();
System.out.println("增加一条数据");
}
}
//下面的方法是使用JDBC连接Oracle数据库
public static Connection getConnection() throws Exception{
Class.forName("oracle.jdbc.OracleDriver");
Connection con = DriverManager.getConnection("jdbc:oracle:thin:@127.0.0.1:1521:ORCl","welkin","123456");
return con;
}
}