JAVA学习笔记15——JDBC

JDBC

1.基本概念
Java DataBase Connectivity:Java数据库连接
本质：定义了一套操作所有关系型数据库的规则，即接口
2.快速入门
导入驱动jar包
在这里插入图片描述
MySQL连接数据库mysql-connector-8.0 jar包使用注意：
https://blog.csdn.net/qq_37137348/article/details/83790382

public class JDBCDemo01 {
    
    
    public static void main(String[] args) throws Exception {
    
    
        //导入驱动jar包
        //注册驱动
        Class.forName("com.mysql.cj.jdbc.Driver");
        //获取数据库连接对象
        Connection con = DriverManager.getConnection("jdbc:mysql://localhost:3306/myemployees?userSSL=false&serverTimezone=UTC", "root", "123456");
        //定义一个sql语句
        String sql="update employees set salary=25000 where employee_id=100";
        //获取执行sql的对象Statement
        Statement statement = con.createStatement();
        //执行sql
        int count = statement.executeUpdate(sql);
        //处理结果
        System.out.println(count);
        //释放资源
        statement.close();
        con.close();
    }
}

DriverManager：驱动管理对象
功能：
1.注册驱动
告诉程序该适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DriveManager
2.获取数据库连接
static Connection getConnection(String url,String user,String password)
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
Connection：数据库连接对象
功能：
1.获取执行sql对象
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()
Statement：
用于执行静态sql并返回其生成的结果的对象
boolean execute(String sql):执行任意sql
int executeUpdate(String sql):执行DML(insert,update,delete)语句，返回影响的行数
ResultSet executeQuery(String ,sql):执行DQL(select)语句，结果集对象，封装查询结果

public class JDBCDemo02 {
    
    
    public static void main(String[] args) {
    
    
        Statement statement=null;
        Connection connection=null;
        try {
    
    
            //注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //定义sql
            String sql="insert into departments values(null,'Los',null,1700)";
            //获取Connection对象
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/myemployees?userSSL=false&serverTimezone=UTC", "root", "199824");
            //获取sql对象statement
            statement = connection.createStatement();
            //执行sql
            int count = statement.executeUpdate(sql);
            //处理结果
            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 throwables) {
    
    
            throwables.printStackTrace();
        }finally{
    
    
            //避免空指针异常
            if (statement!=null){
    
    
                try {
    
    
                    statement.close();
                } catch (SQLException throwables) {
    
    
                    throwables.printStackTrace();
                }
            }
            if (connection!=null){
    
    
                try {
    
    
                    connection.close();
                } catch (SQLException throwables) {
    
    
                    throwables.printStackTrace();
                }
            }
        }
    }
}

其他sql语句类似，修改sql内容即可
Result：
ResultSet：结果集对象，封装查询结果
boolean next():游标向下移动一行
getXxx(参数):获取数据
Xxx代表数据类型
参数，int代表列号(从1开始)，String代表列名称

public class JDBCDemo03 {
    
    
    public static void main(String[] args) {
    
    
        Statement statement=null;
        Connection connection=null;
        ResultSet res=null;
        try {
    
    
            //注册驱动
            Class.forName("com.mysql.cj.jdbc.Driver");
            //定义sql
            String sql="select * from departments where department_id<=100";
            //获取Connection对象
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/myemployees?userSSL=false&serverTimezone=UTC", "root", "199824");
            //获取sql对象statement
            statement = connection.createStatement();
            //执行sql
            res = statement.executeQuery(sql);
            //获取数据
            //让游标向下移动
            res.next();
            int id=res.getInt(1);
            String name=res.getString("department_name");
            int m_id=res.getInt(3);
            int l_id=res.getInt("location_id");
            System.out.println(id+","+name+","+m_id+","+l_id);
        } catch (ClassNotFoundException e) {
    
    
            e.printStackTrace();
        } catch (SQLException throwables) {
    
    
            throwables.printStackTrace();
        }finally{
    
    
            //避免空指针异常
            if (statement!=null){
    
    
                try {
    
    
                    statement.close();
                } catch (SQLException throwables) {
    
    
                    throwables.printStackTrace();
                }
            }
            if (connection!=null){
    
    
                try {
    
    
                    connection.close();
                } catch (SQLException throwables) {
    
    
                    throwables.printStackTrace();
                }
            }
            if (res!=null){
    
    
                try {
    
    
                    res.close();
                } catch (SQLException throwables) {
    
    
                    throwables.printStackTrace();
                }
            }
        }
    }
}

注意：
使用步骤：游标向下移动一行，判断是否有数据，再获取数据
循环判断打印结果

            while(res.next()){
    
    
                int id=res.getInt(1);
                String name=res.getString("department_name");
                int m_id=res.getInt(3);
                int l_id=res.getInt("location_id");
                System.out.println(id+","+name+","+m_id+","+l_id);
            }

JDBC工具类
目的：简化书写
分析：
1.抽取注册驱动
2.抽取方法连接对象。需求：不想传递参数，保证工具类的通用性
解决：配置文件
3.抽取方法释放资源

public class JDBCUtils {
    
    
    //获取连接，return连接对象。采用配置文件，使用静态代码块读取文件
    private static String url;
    private static String user;
    private static String password;
    private static String driver;
    static {
    
    
        //读取文件
        //加载文件
        try {
    
    
            //创建Properties集合类对象
            Properties pro=new Properties();
            //获取src路径下的文件,ClassLoader类加载器
            ClassLoader classLoader = JDBCUtils.class.getClassLoader();
            URL resource = classLoader.getResource("jdbc.properties");
            String path = resource.getPath();
            //加载文件
            pro.load(new FileReader(path));
            //获取数据
            url=pro.getProperty("url");
            user=pro.getProperty("user");
            password=pro.getProperty("password");
            driver=pro.getProperty("driver");
            //注册驱动
            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);
    }
    //释放资源
    public static void close(Statement stmt,Connection conn){
    
    
        if(stmt!=null){
    
    
            try {
    
    
                stmt.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
    
    
            try {
    
    
                conn.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
    }
    //释放资源重载形式
    public static void close(ResultSet res,Statement stmt,Connection conn){
    
    
        if(stmt!=null){
    
    
            try {
    
    
                stmt.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(conn!=null){
    
    
            try {
    
    
                conn.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(res!=null){
    
    
            try {
    
    
                res.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
    }
}

public class Demo4JDBC {
    
    
    public static void main(String[] args) {
    
    
        Connection connection = null;
        Statement stmt = null;
        ResultSet res = null;
        try {
    
    
            //注册驱动
//            Class.forName("com.mysql.jdbc.Driver");
//            //获取数据库连接对象
//            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/myemployees", "root", "lzh199824");
            connection = JDBCUtils.getConnection();
            //定义sql语句
            String sql = "select * from departments where department_id <= 100";
            stmt = connection.createStatement();
            //执行sql
            res = stmt.executeQuery(sql);
            //获取数据
            while (res.next()){
    
    
                int d_id = res.getInt(1);
                String name = res.getString(2);
                int m_id = res.getInt(3);
                int l_id = res.getInt(4);
                System.out.println("department" + d_id + "\r\n" + "name" + name
                                    + "\r\n" + "manager" + m_id + "\r\n" + "location" + l_id);
            }
        } catch (SQLException throwables) {
    
    
            throwables.printStackTrace();
        } finally {
    
    
            JDBCUtils.close(stmt,connection,res);
        }
    }
}

PreparedStatement：
1.sql注入问题
在拼接sql时有一些sql的特殊关键字参与到字符串的拼接，会造成安全性问题
2.解决sql注入
使用PreparedStatement对象
3.预编译sql
参数使用?作为占位符
4。步骤
定义sql时，sql的参数使用？作为占位符
获取执行sql语句的对象 PreparedStatement ，Connection.prepareStatement(String sql)
执行sql，给？赋值。方法：setXxx(参数1，参数2）
参数1位位置，参数2为？的值
后期均会使用PreparedStatement完成增删改查所有操作
可以防止sql注入，效率更高

JDBC控制事务
操作：
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.数据库连接池
概念
其实就是一个容器，存放数据库连接的容器
当系统初始化好后，容器被创建，容器中会申请一些连接对象，当用户来访问数据库时，从容器中获取连接对象，用户访问完后，会将连接对象归还给容器
优点：
节约系统资源
用户访问高效
实现
1.标准接口：DataSource，方法：获取连接，getConnection()
2.由数据库厂商实现，C3P0，Druid
C3P0
1.基本使用

<?xml version="1.0" encoding="utf-8"?>
<c3p0-config>
  <default-config>
    <property name="driverClass">com.mysql.cj.jdbc.Driver</property>
    <property name="jdbcUrl">jdbc:mysql://localhost:3306/myemployees?&amp;useSSL=false&amp;serverTimezone=UTC</property>
    <property name="user">root</property>
    <property name="password">123456</property>
    
    <property name="initialPoolSize">5</property>
    <property name="maxPoolSize">10</property>
    <property name="checkoutTimeout">3000</property>
  </default-config>

  <named-config name="otherc3p0"> 
  </named-config>
</c3p0-config>

注意修改配置文件信息jdbcUrl，如果使用mysqlconnector8要按照如上修改

public class C3P0Demo1 {
    
    
    public static void main(String[] args) throws SQLException {
    
    
        //导入jar包与配置文件
        //创建数据库连接池对象
        DataSource ds=new ComboPooledDataSource();
        //获取连接对象
        Connection connection=ds.getConnection();
        //打印连接对象
        System.out.println(connection);
    }
}

Druid
1.基本使用

driverClassName=com.mysql.cj.jdbc.Driver
url=jdbc:mysql://localhost:3306/myemployees?useSSL=false&useUnicode=true&characterEncoding=UTF8&serverTimezone=GMT&allowPublicKeyRetrieval=true
username=root
password=123456
initialSize=5
maxActive=10
maxWait=3000
minIdle=3
validationQuery:SELECT 1
testWhileIdle:true
testOnBorrow:false
testOnReturn:false

注意url信息，具体见：https://www.cnblogs.com/mjn1/p/11197753.html

public class DruidDemo1 {
    
    
    public static void main(String[] args) throws Exception {
    
    
        //导入jar包
        //定义配置文件
        //加载配置文件
        Properties pro=new Properties();
        InputStream resourceAsStream = DruidDemo1.class.getClassLoader().getResourceAsStream("druid.properties");
        pro.load(resourceAsStream);
        //获取连接池对象
        DataSource ds = DruidDataSourceFactory.createDataSource(pro);
        Connection connection = ds.getConnection();
        System.out.println(connection);
    }
}

2.工具类

public class JDBCUtils {
    
    
    //定义成员变量
    private static DataSource ds;
    static{
    
    
        //加载配置文件
        Properties pro=new Properties();
        try {
    
    
            pro.load(JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties"));
            //获取DataSource
            ds= DruidDataSourceFactory.createDataSource(pro);
        } catch (IOException e) {
    
    
            e.printStackTrace();
        } catch (Exception e) {
    
    
            e.printStackTrace();
        }
    }
    //获取连接
    public static Connection getConnection() throws SQLException {
    
    
        return ds.getConnection();
    }
    //释放资源
    public static void close(Statement stmt,Connection connection){
    
    
        if(stmt!=null){
    
    
            try {
    
    
                stmt.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(connection!=null){
    
    
            try {
    
    
                connection.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
    }
    //重载形式释放资源
    public static void close(ResultSet res,Statement stmt, Connection connection){
    
    
        if(res!=null){
    
    
            try {
    
    
                res.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(stmt!=null){
    
    
            try {
    
    
                stmt.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
        if(connection!=null){
    
    
            try {
    
    
                connection.close();
            } catch (SQLException throwables) {
    
    
                throwables.printStackTrace();
            }
        }
    }
    public static DataSource getDataSourece(){
    
    
        return ds;
    }
}

4.JDBCTemplate
1.基本入门

public class JDBCTemplateDemo1 {
    
    
    public static void main(String[] args) {
    
    
        //导入jar包
        //创建JDBCTemplate对象
        JdbcTemplate template=new JdbcTemplate(JDBCUtils.getDataSourece());
        //调用方法
        String sql="update employees set salary=? where employee_id=?";
        int count = template.update(sql, 30000, 100);
        System.out.println(count);
    }
}

2.JDBCTemplate方法
update():执行DML语句，增删改
queryForMap():查询结果将结果封装为map集合
queryForList():查询结果将结果封装为list集合
query():查询结果将结果封装为JavaBean对象
queryForObject():查询结果将结果封装为对象

public class JDBCTemplateDemo1 {
    
    
    //创建JDBCTemplate对象
    private JdbcTemplate template=new JdbcTemplate(JDBCUtils.getDataSourece());
    @Test
    public void test1(){
    
    
        //queryForMap():查询结果将结果封装为map集合
        String sql="select * from departments where department_id=?";
        Map<String, Object> map = template.queryForMap(sql, 100);
        System.out.println(map);
    }
    @Test
    public void test2(){
    
    
        //queryForList():查询结果将结果封装为list集合
        String sql="select * from departments where department_id<=?";
        List<Map<String, Object>> list = template.queryForList(sql, 100);
        for (Map<String, Object> dp : list) {
    
    
            for (Map.Entry<String, Object> entry : dp.entrySet()) {
    
    
                System.out.print(entry.getKey()+":"+entry.getValue()+"\t");
            }
            System.out.println();
        }
    }
    @Test
    public void test3(){
    
    
        //query():查询结果将结果封装为JavaBean对象(实际情况)
        String sql="select * from departments where department_id<=?";
        List<Department> list = template.query(sql, new RowMapper<Department>() {
    
    
            @Override
            public Department mapRow(ResultSet rs, int i) throws SQLException {
    
    
                int id = rs.getInt("department_id");
                String name = rs.getString("department_name");
                int m_id = rs.getInt("manager_id");
                int l_id = rs.getInt("location_id");
                Department dpt = new Department(id, name, m_id, l_id);
                return dpt;
            }
        },100);
        for (Department dpt : list) {
    
    
            System.out.println(dpt);
        }
    }
    @Test
    public void test4(){
    
    
        /*
        一般我们使用BeanPropertyRowMapper实现类
        可以完成数据到JavaBean的自动封装
        new BeanPropertyRowMapper<类型>(类型.class)
         */
        String sql="select * from departments where department_id<=?";
        List<Department> list = template.query(sql, new BeanPropertyRowMapper<>(Department.class),100);
        for (Department dpt : list) {
    
    
            System.out.println(dpt);
        }
    }
    @Test
    public void test5(){
    
    
        //queryForObject():查询结果将结果封装为对象
        String sql="select count(department_id) from departments where department_id<=?";
        Long total=template.queryForObject(sql, Long.class,100);
        System.out.println(total);
    }
}

JAVA学习笔记15——JDBC

JDBC

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