关于java:2020想学习JAVA的同学看过来最基础的编程CRUD你会了没

一 JDBC简介

Java DataBase Connectivity Java语言连贯数据库

官网(Sun公司)定义的一套操作所有关系型数据库的规定(接口) 各个数据库厂商去实现这套接口提供数据库驱动JAR包能够应用这套接口(JDBC)编程真正执行的代码是驱动JAR包中的实现类

二 JDBC初体验

1. 新建一个Maven我的项目

pom.xml<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0"         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">    <modelVersion>4.0.0</modelVersion>    <groupId>com.hy.jdbc</groupId>    <artifactId>jdbc-demo</artifactId>    <version>1.0-SNAPSHOT</version>    <!-- 定义依赖版本号 -->    <properties>        <junit.version>4.12</junit.version>        <mysql-connector-java.version>8.0.11</mysql-connector-java.version>        <druid.version>1.1.10</druid.version>    </properties>    <!-- 治理jar版本号 -->    <dependencyManagement>        <dependencies>            <!-- junit -->            <dependency>                <groupId>junit</groupId>                <artifactId>junit</artifactId>                <version>${junit.version}</version>            </dependency>            <!-- mysql -->            <dependency>                <groupId>mysql</groupId>                <artifactId>mysql-connector-java</artifactId>                <version>${mysql-connector-java.version}</version>            </dependency>            <dependency>                <groupId>com.alibaba</groupId>                <artifactId>druid</artifactId>                <version>${druid.version}</version>            </dependency>        </dependencies>    </dependencyManagement>    <dependencies>        <!-- junit -->        <dependency>            <groupId>junit</groupId>            <artifactId>junit</artifactId>        </dependency>        <!-- mysql -->        <dependency>            <groupId>mysql</groupId>            <artifactId>mysql-connector-java</artifactId>        </dependency>        <dependency>            <groupId>com.alibaba</groupId>            <artifactId>druid</artifactId>        </dependency>    </dependencies></project>

sql

CREATE TABLE account (    aid INT PRIMARY KEY,    aname VARCHAR(100),    amoney DOUBLE);

2. 插入

@Testpublic void test01() {    Connection connection = null;    PreparedStatement statement = null;    try {        // 注册驱动 MySQL5之后的驱动JAR包能够省略该步骤        Class.forName("com.mysql.cj.jdbc.Driver");        // 获取数据库连贯对象 Connection        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");        // 开启事务        connection.setAutoCommit(false);        // 定义SQL        String sql = "insert into account values(?, ?, ?)";        // 获取执行SQL的对象 PreparedStatement        statement = connection.prepareStatement(sql);        // 设置参数        statement.setInt(1, 1); //'?' 地位的编号 从1开始        statement.setString(2, "No1"); //'?' 地位的编号 从1开始        statement.setDouble(3, 2000); //'?' 地位的编号 从1开始        // 执行SQL 返回受影响的行数        int count = statement.executeUpdate();        // 提交事务        connection.commit();        // 处理结果        System.out.println("count = " + count);    } catch (Exception e) {        e.printStackTrace();        // 回滚事务        if (null != connection) {            try {                connection.rollback();            } catch (SQLException exception) {                exception.printStackTrace();            }        }    } finally {        // 开释资源        if (null != statement) {            try {                statement.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != connection) {            try {                connection.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

3. 删除

@Testpublic void test02() {    Connection connection = null;    PreparedStatement statement = null;    try {        // 注册驱动 MySQL5之后的驱动JAR包能够省略该步骤        //Class.forName("com.mysql.cj.jdbc.Driver");        // 获取数据库连贯对象 Connection        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");        // 开启事务        connection.setAutoCommit(false);        // 定义SQL        String sql = "delete from account where aid = ?";        // 获取执行SQL的对象 PreparedStatement        statement = connection.prepareStatement(sql);        // 设置参数        statement.setInt(1, 1); //'?' 地位的编号 从1开始        // 执行SQL 返回受影响的行数        int count = statement.executeUpdate();        // 提交事务        connection.commit();        // 处理结果        System.out.println("count = " + count);    } catch (Exception e) {        e.printStackTrace();        // 回滚事务        if (null != connection) {            try {                connection.rollback();            } catch (SQLException exception) {                exception.printStackTrace();            }        }    } finally {        // 开释资源        if (null != statement) {            try {                statement.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != connection) {            try {                connection.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

4. 批改

@Testpublic void test03() {    Connection connection = null;    PreparedStatement statement1 = null;    PreparedStatement statement2 = null;    try {        // 注册驱动 MySQL5之后的驱动JAR包能够省略该步骤        Class.forName("com.mysql.cj.jdbc.Driver");        // 获取数据库连贯对象 Connection        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");        // 开启事务        connection.setAutoCommit(false);        // 定义SQL        String sql1 = "update account set amoney = amoney + ? where aid = ?";        String sql2 = "update account set amoney = amoney - ? where aid = ?";        // 获取执行SQL的对象 PreparedStatement        statement1 = connection.prepareStatement(sql1);        statement2 = connection.prepareStatement(sql2);        // 设置参数        statement1.setDouble(1, 500); //'?' 地位的编号 从1开始        statement1.setInt(2, 1); //'?' 地位的编号 从1开始        statement2.setDouble(1, 500); //'?' 地位的编号 从1开始        statement2.setInt(2, 2); //'?' 地位的编号 从1开始        // 执行SQL 返回受影响的行数        statement1.executeUpdate();        int i = 3 / 0; //模仿异样        statement2.executeUpdate();        // 提交事务        connection.commit();    } catch (Exception e) {        e.printStackTrace();        // 回滚事务        if (null != connection) {            try {                connection.rollback();            } catch (SQLException exception) {                exception.printStackTrace();            }        }    } finally {        // 开释资源        if (null != statement2) {            try {                statement2.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != statement1) {            try {                statement1.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != connection) {            try {                connection.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

5. 查问

@Testpublic void test04() {    Connection connection = null;    PreparedStatement statement = null;    ResultSet resultSet = null;    try {        // 注册驱动 MySQL5之后的驱动JAR包能够省略该步骤        Class.forName("com.mysql.cj.jdbc.Driver");        // 获取数据库连贯对象 Connection        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/demo_hy", "root", "root");        // 开启事务        connection.setAutoCommit(false);        // 定义SQL        String sql = "select * from account";        // 获取执行SQL的对象 PreparedStatement        statement = connection.prepareStatement(sql);        // 执行SQL 返回后果集        resultSet = statement.executeQuery();        // 提交事务        connection.commit();        // 处理结果        while (resultSet.next()) {            int id = resultSet.getInt(1); //代表列的编号 从1开始            String name = resultSet.getString("aname"); //代表列的名称            double money = resultSet.getDouble(3); //代表列的编号 从1开始            System.out.println(id + "---" + name + "---" + money);        }    } catch (Exception e) {        e.printStackTrace();        // 回滚事务        if (null != connection) {            try {                connection.rollback();            } catch (SQLException exception) {                exception.printStackTrace();            }        }    } finally {        // 开释资源        if (null != resultSet) {            try {                resultSet.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != statement) {            try {                statement.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != connection) {            try {                connection.close();            } catch (SQLException e) {                e.printStackTrace();            }        }    }}

三数据库连接池

一个寄存数据库连贯的容器

当零碎初始化后容器被创立容器中会申请一些连贯对象当用户拜访数据库时从容器中获取连贯对象用户拜访完之后会将连贯对象归还给容器这样能够节约资源进步拜访效率

常见的数据库连接池有 Druid C3P0...

Druid初体验

druid.properties

url=jdbc:mysql://localhost:3306/demo_hydriverClassName=com.mysql.cj.jdbc.Driverusername=rootpassword=rootmaxActive=10minIdle=5

XTest.java

@Testpublic void test05() {    InputStream stream = null;    Connection connection = null;    PreparedStatement statement = null;    ResultSet resultSet = null;    try {        // 加载配置文件        Properties properties = new Properties();        stream = XTest.class.getClassLoader().getResourceAsStream("druid.properties");        properties.load(stream);        // 获取连接池对象        DataSource dataSource = DruidDataSourceFactory.createDataSource(properties);        // 获取数据库连贯对象 Connection        connection = dataSource.getConnection();        // 开启事务        connection.setAutoCommit(false);        // 定义SQL        String sql = "select * from account";        // 获取执行SQL的对象 PreparedStatement        statement = connection.prepareStatement(sql);        // 执行SQL 返回后果集        resultSet = statement.executeQuery();        // 提交事务        connection.commit();        // 处理结果        while (resultSet.next()) {            int id = resultSet.getInt(1); //代表列的编号 从1开始            String name = resultSet.getString("aname"); //代表列的名称            double money = resultSet.getDouble(3); //代表列的编号 从1开始            System.out.println(id + "---" + name + "---" + money);        }    } catch (Exception e) {        e.printStackTrace();        // 回滚事务        if (null != connection) {            try {                connection.rollback();            } catch (SQLException exception) {                exception.printStackTrace();            }        }    } finally {        // 开释资源        if (null != resultSet) {            try {                resultSet.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != statement) {            try {                statement.close();            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != connection) {            try {                connection.close(); //偿还连贯            } catch (SQLException e) {                e.printStackTrace();            }        }        if (null != stream) {            try {                stream.close();            } catch (IOException e) {                e.printStackTrace();            }        }    }}

最初

学习java不易，须要继续的保持，如果有想学习java的基础知识或者进阶java的能够私信“学习”获取学习联系方式

一 JDBC简介

二 JDBC初体验

三 数据库连接池

最初

三数据库连接池