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:

<?xml version="1.0" encoding="gb2312"?>
<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=123456

3.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;}@Overridepublic 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<ServiceDetail> findAll(){Connection con = null;PreparedStatement stmt = null;try{con = openConnection();stmt = com.prepareStatement(FIND_ALL);ResultSet rs = stmt.executeQuery();List<ServiceDetail> list = new ArrayList<ServiceDetail>();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;}
}