An introduction to JDBC
Java DataBase Connectivity Java language to connect to the database
The official (Sun company) defines a set of rules (interfaces) for operating all relational databases. Each database manufacturer implements this set of interfaces. Provides database driver JAR packages. You can use this set of interface (JDBC) programming. The code that is actually executed is the driver JAR package. Implementation class
Two JDBC first experience
1. Create a new Maven project
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>
<!-- 管理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. Insert
@Test
public void test01() {
Connection connection = null;
PreparedStatement statement = null;
try {
// 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
Class.forName("com.mysql.cj.jdbc.Driver");
// 获取数据库连接对象 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); //'?' 位置的编号 从1开始
statement.setString(2, "No1"); //'?' 位置的编号 从1开始
statement.setDouble(3, 2000); //'?' 位置的编号 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 {
// 释放资源
if (null != statement) {
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (null != connection) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}3. Delete
@Test
public void test02() {
Connection connection = null;
PreparedStatement statement = null;
try {
// 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
//Class.forName("com.mysql.cj.jdbc.Driver");
// 获取数据库连接对象 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); //'?' 位置的编号 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 {
// 释放资源
if (null != statement) {
try {
statement.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
if (null != connection) {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}4. Modification
@Test
public void test03() {
Connection connection = null;
PreparedStatement statement1 = null;
PreparedStatement statement2 = null;
try {
// 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
Class.forName("com.mysql.cj.jdbc.Driver");
// 获取数据库连接对象 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); //'?' 位置的编号 从1开始
statement1.setInt(2, 1); //'?' 位置的编号 从1开始
statement2.setDouble(1, 500); //'?' 位置的编号 从1开始
statement2.setInt(2, 2); //'?' 位置的编号 从1开始
// 执行SQL 返回受影响的行数
statement1.executeUpdate();
int i = 3 / 0; //模拟异常
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 {
// 释放资源
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. Query
@Test
public void test04() {
Connection connection = null;
PreparedStatement statement = null;
ResultSet resultSet = null;
try {
// 注册驱动 MySQL5之后的驱动JAR包可以省略该步骤
Class.forName("com.mysql.cj.jdbc.Driver");
// 获取数据库连接对象 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 返回结果集
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 {
// 释放资源
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();
}
}
}
}Three database connection pool
A container for storing database connections
When the system is initialized, the container is created. The container will apply for some connection objects. When the user accesses the database, the connection object is obtained from the container. After the user accesses the database, the connection object will be returned to the container. This saves resources and improves access efficiency.
Common database connection pools include Druid C3P0...
Druid first experience
druid.properties
url=jdbc:mysql://localhost:3306/demo_hy
driverClassName=com.mysql.cj.jdbc.Driver
username=root
password=root
maxActive=10
minIdle=5
XTest.java
@Test
public 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);
// 获取数据库连接对象 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 返回结果集
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 {
// 释放资源
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(); //归还连接
} catch (SQLException e) {
e.printStackTrace();
}
}
if (null != stream) {
try {
stream.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}At last
Learning java is not easy, it needs continuous persistence. If you want to learn the basics of java or advanced java, you can privately "learn" to get the learning contact information
