1. JDBC基本概念
2. 快速入门
3. 对JDBC中各个接口和类详解
JDBC:
1. 概念:Java DataBase Connectivity Java 数据库连接, Java语言操作数据库
* JDBC本质:其实是官方(sun公司)定义的一套操作所有关系型数据库的规则,即接口。各个数据库厂商去实现这套接口,提供数据库驱动jar包。我们可以使用这套接口(JDBC)编程,真正执行的代码是驱动jar包中的实现类。
2. 快速入门:
* 步骤:
1. 导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
1.复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
2.右键-->Add As Library
2. 注册驱动
3. 获取数据库连接对象 Connection
4. 定义sql
5. 获取执行sql语句的对象 Statement
6. 执行sql,接受返回结果
7. 处理结果
8. 释放资源
* 代码实现:
Class. forName ( "com.mysql.jdbc.Driver" ) ;
Connection conn = DriverManager. getConnection ( "jdbc:mysql://localhost:3306/db3" , "root" , "root" ) ;
String sql = "update account set balance = 500 where id = 1" ;
Statement stmt = conn. createStatement ( ) ;
int count = stmt. executeUpdate ( sql) ;
System. out. println ( count) ;
stmt. close ( ) ;
conn. close ( ) ;
3. 详解各个对象:
1. DriverManager:驱动管理对象
* 功能:
1. 注册驱动:告诉程序该使用哪一个数据库驱动jar
static void registerDriver(Driver driver) :注册与给定的驱动程序 DriverManager 。
写代码使用: Class.forName("com.mysql.jdbc.Driver");
通过查看源码发现:在com.mysql.jdbc.Driver类中存在静态代码块
static {
try {
java.sql.DriverManager.registerDriver(new Driver());
} catch (SQLException E) {
throw new RuntimeException("Can't register driver!");
}
}
注意:mysql5之后的驱动jar包可以省略注册驱动的步骤。
2. 获取数据库连接:
* 方法:static Connection getConnection(String url, String user, String password)
* 参数:
* url:指定连接的路径
* 语法:jdbc:mysql://ip地址(域名):端口号/数据库名称
* 例子:jdbc:mysql://localhost:3306/db3
* 细节:如果连接的是本机mysql服务器,并且mysql服务默认端口是3306,则url可以简写为:jdbc:mysql:///数据库名称
* user:用户名
* password:密码
2. Connection:数据库连接对象
1. 功能:
1. 获取执行sql 的对象
* Statement createStatement()
* PreparedStatement prepareStatement(String sql)
2. 管理事务:
* 开启事务:setAutoCommit(boolean autoCommit) :调用该方法设置参数为false,即开启事务
* 提交事务:commit()
* 回滚事务:rollback()
3. Statement:执行sql的对象
1. 执行sql
1. boolean execute(String sql) :可以执行任意的sql (一般不用这个)
2. int executeUpdate(String sql) :执行DML(insert、update、delete)语句、DDL(create,alter、drop)语句
* 返回值:影响的行数,可以通过这个影响的行数判断DML语句是否执行成功 返回值>0的则执行成功,反之,则失败。
3. ResultSet executeQuery(String sql) :执行DQL(select)语句
2. 练习:
1. account表 添加一条记录
2. account表 修改记录
3. account表 删除一条记录
代码:
Statement stmt = null;
Connection conn = null;
try {
Class. forName ( "com.mysql.jdbc.Driver" ) ;
String sql = "insert into account values(null,'王五',3000)" ;
conn = DriverManager. getConnection ( "jdbc:mysql:///db3" , "root" , "root" ) ;
stmt = conn. createStatement ( ) ;
int count = stmt. executeUpdate ( sql) ;
System. out. println ( count) ;
if ( count > 0 ) {
System. out. println ( "添加成功!" ) ;
} else {
System. out. println ( "添加失败!" ) ;
}
} catch ( ClassNotFoundException e) {
e. printStackTrace ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
} finally {
if ( stmt != null) {
try {
stmt. close ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
}
}
if ( conn != null) {
try {
conn. close ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
}
}
}
4. ResultSet:结果集对象,封装查询结果
* boolean next(): 游标向下移动一行,判断当前行是否是最后一行末尾(是否有数据),如果是,则返回false,如果不是则返回true
* getXxx(参数):获取数据
* Xxx:代表数据类型 如: int getInt() , String getString()
* 参数:
1. int:代表列的编号,从1开始 如: getString(1)
2. String:代表列名称。 如: getDouble("balance")
* 注意:
* 使用步骤:
1. 游标向下移动一行
2. 判断是否有数据
3. 获取数据
while ( rs. next ( ) ) {
int id = rs. getInt ( 1 ) ;
String name = rs. getString ( "name" ) ;
double balance = rs. getDouble ( 3 ) ;
System. out. println ( id + "---" + name + "---" + balance) ;
}
* 练习:
* 定义一个方法,查询emp表的数据将其封装为对象,然后装载集合,返回。
1. 定义Emp类
2. 定义方法 public List<Emp> findAll(){}
3. 实现方法 select * from emp;
public static void main ( String[ ] args) {
List< Emp> list = new JDBCDemo8 ( ) . findAll2 ( ) ;
System. out. println ( list) ;
System. out. println ( list. size ( ) ) ;
}
public List< Emp> findAll ( ) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
List< Emp> list = null;
try {
Class. forName ( "com.mysql.jdbc.Driver" ) ;
conn = DriverManager. getConnection ( "jdbc:mysql:///db3" , "root" , "root" ) ;
String sql = "select * from emp" ;
stmt = conn. createStatement ( ) ;
rs = stmt. executeQuery ( sql) ;
Emp emp = null;
list = new ArrayList < Emp> ( ) ;
while ( rs. next ( ) ) {
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" ) ;
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) ;
list. add ( emp) ;
}
} catch ( ClassNotFoundException e) {
e. printStackTrace ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
} finally {
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 ( ) ;
}
}
}
return list;
}
5. PreparedStatement:执行sql的对象
1. SQL注入问题:在拼接sql时,有一些sql的特殊关键字参与字符串的拼接。会造成安全性问题
1. 输入用户随便,输入密码:a' or 'a' = 'a
2. sql:select * from user where username = 'fhdsjkf' and password = 'a' or 'a' = 'a'
2. 解决sql注入问题:使用PreparedStatement对象来解决
3. 预编译的SQL:参数使用?作为占位符
4. 步骤:
1. 导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
2. 注册驱动
3. 获取数据库连接对象 Connection
4. 定义sql
* 注意:sql的参数使用?作为占位符。 如:select * from user where username = ? and password = ?;
5. 获取执行sql语句的对象 PreparedStatement Connection.prepareStatement(String sql)
6. 给?赋值:
* 方法: setXxx(参数1,参数2)
* 参数1:?的位置编号 从1 开始
* 参数2:?的值
7. 执行sql,接受返回结果,不需要传递sql语句
8. 处理结果
9. 释放资源
5. 注意:后期都会使用PreparedStatement来完成增删改查的所有操作
1. 可以防止SQL注入
2. 效率更高
抽取JDBC工具类 : JDBCUtils
* 目的:简化书写
* 分析:
1. 注册驱动也抽取
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
* 代码实现:
public class JDBCUtils {
private static String url;
private static String user;
private static String password;
private static String driver;
static {
try {
Properties pro = new Properties ( ) ;
ClassLoader classLoader = JDBCUtils. class . getClassLoader ( ) ;
URL res = classLoader. getResource ( "jdbc.properties" ) ;
String path = res. getPath ( ) ;
System. out. println ( path) ;
pro. load ( new FileReader ( path) ) ;
url = pro. getProperty ( "url" ) ;
user = pro. getProperty ( "user" ) ;
password = pro. getProperty ( "password" ) ;
driver = pro. getProperty ( "driver" ) ;
Class. forName ( driver) ;
} catch ( IOException e) {
e. printStackTrace ( ) ;
} catch ( ClassNotFoundException e) {
e. printStackTrace ( ) ;
}
}
public static Connection getConnection ( ) throws SQLException {
return DriverManager. getConnection ( url, user, password) ;
}
public static void close ( Statement stmt, Connection conn) {
if ( stmt != null) {
try {
stmt. close ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
}
}
if ( conn != null) {
try {
conn. close ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
}
}
}
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 ( ) ;
}
}
}
}
public List< Emp> findAll2 ( ) {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
List< Emp> list = null;
try {
conn = JDBCUtils. getConnection ( ) ;
String sql = "select * from emp" ;
stmt = conn. createStatement ( ) ;
rs = stmt. executeQuery ( sql) ;
Emp emp = null;
list = new ArrayList < Emp> ( ) ;
while ( rs. next ( ) ) {
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" ) ;
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) ;
list. add ( emp) ;
}
} catch ( SQLException e) {
e. printStackTrace ( ) ;
} finally {
JDBCUtils. close ( rs, stmt, conn) ;
}
return list;
}
}
```bash
url= jdbc: mysql: /
user= root
password= root
driver= com. mysql. jdbc. Driver
* 练习:
* 需求:
1. 通过键盘录入用户名和密码
2. 判断用户是否登录成功
* select * from user where username = "" and password = "";
* 如果这个sql有查询结果,则成功,反之,则失败
* 步骤:
1. 创建数据库表 user
```bash
CREATE TABLE USER(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(32),
PASSWORD VARCHAR(32)
);
INSERT INTO USER VALUES(NULL,'zhangsan','123');
INSERT INTO USER VALUES(NULL,'lisi','234');
2. 代码实现:
public class JDBCDemo9 {
public static void main ( String[ ] args) {
Scanner sc = new Scanner ( System. in) ;
System. out. println ( "请输入用户名:" ) ;
String username = sc. nextLine ( ) ;
System. out. println ( "请输入密码:" ) ;
String password = sc. nextLine ( ) ;
boolean flag = new JDBCDemo9 ( ) . login ( username, password) ;
if ( flag) {
System. out. println ( "登录成功!" ) ;
} else {
System. out. println ( "用户名或密码错误!" ) ;
}
}
public boolean login ( String username , String password) {
if ( username == null || password == null) {
return false ;
}
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
conn = JDBCUtils. getConnection ( ) ;
String sql = "select * from user where username = '" + username+ "' and password = '" + password+ "' " ;
stmt = conn. createStatement ( ) ;
rs = stmt. executeQuery ( sql) ;
return rs. next ( ) ;
} catch ( SQLException e) {
e. printStackTrace ( ) ;
} finally {
JDBCUtils. close ( rs, stmt, conn) ;
}
return false ;
}
}
JDBC控制事务:
1. 事务:一个包含多个步骤的业务操作。如果这个业务操作被事务管理,则这多个步骤要么同时成功,要么同时失败。
2. 操作:
1. 开启事务
2. 提交事务
3. 回滚事务
3. 使用Connection对象来管理事务
* 开启事务:setAutoCommit(boolean autoCommit) :调用该方法设置参数为false,即开启事务
* 在执行sql之前开启事务
* 提交事务:commit()
* 当所有sql都执行完提交事务
* 回滚事务:rollback()
* 在catch中回滚事务
4. 代码:
public class JDBCDemo10 {
public static void main ( String[ ] args) {
Connection conn = null;
PreparedStatement pstmt1 = null;
PreparedStatement pstmt2 = null;
try {
conn = JDBCUtils. getConnection ( ) ;
conn. setAutoCommit ( false ) ;
String sql1 = "update account set balance = balance - ? where id = ?" ;
String sql2 = "update account set balance = balance + ? where id = ?" ;
pstmt1 = conn. prepareStatement ( sql1) ;
pstmt2 = conn. prepareStatement ( sql2) ;
pstmt1. setDouble ( 1 , 500 ) ;
pstmt1. setInt ( 2 , 1 ) ;
pstmt2. setDouble ( 1 , 500 ) ;
pstmt2. setInt ( 2 , 2 ) ;
pstmt1. executeUpdate ( ) ;
int i = 3 / 0 ;
pstmt2. executeUpdate ( ) ;
conn. commit ( ) ;
} catch ( Exception e) {
try {
if ( conn != null) {
conn. rollback ( ) ;
}
} catch ( SQLException e1) {
e1. printStackTrace ( ) ;
}
e. printStackTrace ( ) ;
} finally {
JDBCUtils. close ( pstmt1, conn) ;
JDBCUtils. close ( pstmt2, null) ;
}
}
}