Java入坑之 数据库编程
一、基础概念
1.1JDBC 步骤
导入驱动jar包
注册驱动
获取数据库连接对象 Connection
DataSource dSource;
dSource.getConnection();
定义sql语句
String sql = "update account set balance = 500 where id = 1";
获取执行sql语句的对象 Statement
PreparedStatement stmt = conn. prepareStatement(sql)；
执行sql，接受返回结果
int count = stmt.executeUpdate(sql);
处理结果 System.out.println(count);
释放资源 stmt.close(); conn.close();
1.2相关类介绍
1.3相关代码
在Maven中声明MySQL的JDBC实现依赖
1.3.1查询
package org.example;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class SelectTest {
public static void main(String[] args) {
// 注册 MySQL 驱动
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
return;
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建 Java 和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
System.out.println("连接数据库成功！");
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建 Statement 成功！");
// 执行 SQL 语句并返回结果到 ResultSet
ResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");
// 开始遍历 ResultSet 数据
while (rs.next()) {
System.out.println(rs.getInt(1) + "," + rs.getString(2) + "," + rs.getInt("price"));
}
rs.close();
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
System.out.println("关闭数据库连接成功！");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
1.3.2增删改
package org.example;
import java.sql.*;
public class UpdateTest {
public static void main(String[] args) {
executeUpdate("update book set price = 300 where bookid = 1");
executeUpdate("insert into book(bookid, bookname, price) values(4, '编译原理', 90)");
executeUpdate("delete from book where bookid = 4");
}
/**
* 执行数据更新操作
* @param sql 要执行的 SQL 语句
*/
public static void executeUpdate(String sql) {
// 注册 MySQL 驱动
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建 Java 和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
System.out.println("连接数据库成功！");
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建 Statement 成功！");
int rs = stmt.executeUpdate(sql);
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
System.out.println("关闭数据库连接成功！");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
1.3.3事务逻辑
package org.example;
import java.sql.*;
public class TransactionTest {
public static void main(String[] args) throws Exception {
// 构建Java和数据库之间的桥梁介质
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
conn.setAutoCommit(false);
insertBook(conn, "insert into book values(101, 'aaaa', 10)");
insertBook(conn, "insert into book values(102, 'bbbb', 10)");
insertBook(conn, "insert into book values(103, 'cccc', 10)");
Savepoint phase1 = conn.setSavepoint(); // 设置一个保存点
insertBook(conn, "insert into book values(104, 'cccc', 10)");
insertBook(conn, "insert into book values(105, 'cccc', 10)");
conn.rollback(phase1); // 回滚到phase1保存点，即上面2行无效
conn.commit();
System.out.println("操作成功");
} catch (SQLException e) {
e.printStackTrace();
conn.rollback();
} finally {
if (null != conn) {
conn.close();
}
}
}
public static void insertBook(Connection conn, String sql) {
try {
// 构建数据库执行者
Statement stmt = conn.createStatement();
// 执行SQL语句
int result = stmt.executeUpdate(sql);
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
1.3.4拼接字符串
package org.example;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
import java.sql.Statement;
public class InsertTest {
public static void main(String[] a) {
//concatInsertBook();
unsafeConcatInsertBook();
}
public static void concatInsertBook() {
// 构建Java和数据库之间的桥梁介质
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建Statement成功！");
// 执行SQL语句
int bookid = 11;
String bookName = "Effective Java";
int price = 50;
String sql = "insert into book(bookid,bookname,price) values("
+ bookid + ", '" + bookName + "', " + price + ")";
int result = stmt.executeUpdate(sql);
stmt.close();
System.out.println("操作成功");
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void unsafeConcatInsertBook() {
// 构建Java和数据库之间的桥梁介质
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建Statement成功！");
// 执行SQL语句
int bookid = 13;
String bookName = "Effective Java',50);delete from t_book;insert into t_book values(101, 'faked book";
int price = 50;
String sql = "insert into book(bookid,bookname,price) values("
+ bookid + ", '" + bookName + "', " + price + ");";
System.out.println(sql);
int result = stmt.executeUpdate(sql);
stmt.close();
System.out.println("操作成功");
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
1.3.5batch函数
package org.example;
import java.sql.*;
public class InsertTest1 {
public static void main(String[] a) {
safeInsertBook();
batchInsertBook();
}
public static void safeInsertBook() {
Connection conn = null;
try {
// 注册 MySQL 驱动
Class.forName("com.mysql.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
String sql = "insert into book(bookid,bookname,price) values (?, ?, ?)";
// 构建数据库执行者
PreparedStatement pstmt = conn.prepareStatement(sql);
// 设置参数
int bookid = 15;
String bookName = "Effective Java',50);delete from t_book;insert into t_book values(101, 'faked book";
int price = 50;
pstmt.setInt(1, bookid);
pstmt.setString(2, bookName);
pstmt.setInt(3, price);
// 执行SQL语句
int result = pstmt.executeUpdate();
pstmt.close();
System.out.println("操作成功");
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
System.out.println("关闭数据库连接成功！");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void batchInsertBook() {
Connection conn = null;
try {
// 注册 MySQL 驱动
Class.forName("com.mysql.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
String sql = "insert into book(bookid,bookname,price) values (?,?,?)";
// 构建数据库执行者
PreparedStatement pstmt = conn.prepareStatement(sql);
// 设置参数
String bookName = "aaaaaaaaaaaaaaaa";
int price;
// 执行批量插入操作
for (int i = 210; i < 202; i++) {
price = 50;
pstmt.setInt(1, i);
pstmt.setString(2, bookName);
pstmt.setInt(3, price);
pstmt.addBatch();
}
pstmt.executeBatch();
pstmt.close();
System.out.println("操作成功");
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
System.out.println("关闭数据库连接成功！");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
如果有大量的sq语句，它们结构相同，仅仅差别在具体数值上，那么可以通过addBatch
方法进行批量操作。这样会提高性能，减少数据库负担。
1.3.6ResultSetMetaData类
package org.example;
import java.sql.*;
public class ResultSetMetaDataTest {
public static void main(String[] args) {
// 构建Java和数据库之间的桥梁介质
try {
Class.forName("com.mysql.cj.jdbc.Driver");
System.out.println("注册驱动成功!");
} catch (ClassNotFoundException e1) {
System.out.println("注册驱动失败!");
e1.printStackTrace();
return;
}
String url = "jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC";
Connection conn = null;
try {
// 构建Java和数据库之间的桥梁：URL，用户名，密码
conn = DriverManager.getConnection(url, "root", "b123456");
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建Statement成功！");
// 执行SQL语句并返回结果到ResultSet
ResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");
// 获取结果集的元数据
ResultSetMetaData meta = rs.getMetaData();
int cols = meta.getColumnCount();
for (int i = 1; i <= cols; i++) {
System.out.println(meta.getColumnName(i) + "," + meta.getColumnTypeName(i));
}
rs.close();
stmt.close();
} catch (SQLException e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
二、数据库连接池
2.1流程重述
2.2亨元模式
享元模式, Flyweight Pattern
- 经典23个设计模式的一种，属于结构型模式。
- 一个系统中存在大量的相同的对象，由于这类对象的大量使用，会造成系统内存的耗费，可以使用享元模式来减少系统中对象的数量。
2.3 数据库连接池概念
2.4C3P0连接池
2.4.1配置文件
com.mchange
c3p0
0.9.5.2
com.alibaba
druid
1.1.10
2.4.2相关代码
package org.example;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
public class SelectTest1 {
public static void main(String[] args) {
Connection conn = null;
try {
// 从c3p0获取数据库连接
conn = C3p0Factory1.getConnection();
//conn = C3p0Factory2.getConnection();
从Druid获取
conn = DruidFactory1.getConnection();
//conn = DruidFactory2.getConnection();
// 构建数据库执行者
Statement stmt = conn.createStatement();
System.out.println("创建Statement成功！");
// 执行SQL语句并返回结果到ResultSet
ResultSet rs = stmt.executeQuery("select bookid, bookname, price from book order by bookid");
// 开始遍历ResultSet数据
while (rs.next()) {
System.out.println(rs.getInt(1) + "," + rs.getString(2) + "," + rs.getInt("price"));
}
rs.close();
stmt.close();
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
if (conn != null) {
conn.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}
2.4.3相关配置
com.mysql.jdbc.Driver
jdbc:mysql://localhost:3306/test
root
123456
5
20
package org.example;
import com.mchange.v2.c3p0.ComboPooledDataSource;
import java.sql.Connection;
public class C3p0Factory2 {
private static ComboPooledDataSource dataSource = null;
public static void init() throws Exception {
// 创建 ComboPooledDataSource 实例，会自动加载 c3p0-config.xml 文件的配置
dataSource = new ComboPooledDataSource();
// 此时 dataSource 是一个完全配置好的可用连接池 DataSource
}
public static Connection getConnection() throws Exception {
if (null == dataSource) {
init();
}
// 返回从连接池获取的数据库连接
return dataSource.getConnection();
}
}
2.4.4 DruidData类
package org.example;
import com.alibaba.druid.pool.DruidDataSource;
import java.sql.Connection;
public class DruidFactory1 {
private static DruidDataSource dataSource = null;
public static void init() throws Exception {
dataSource = new DruidDataSource();
dataSource.setDriverClassName("com.mysql.jdbc.Driver");
dataSource.setUsername("root");
dataSource.setPassword("b123456");
dataSource.setUrl("jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC");
dataSource.setInitialSize(5);
dataSource.setMinIdle(1);
dataSource.setMaxActive(10);
// 启用监控统计功能
dataSource.setFilters("stat");
}
public static Connection getConnection() throws Exception {
if (null == dataSource) {
init();
}
return dataSource.getConnection();
}
}
2.4.6配置
driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/t_book?serverTimezone=UTC
username=root
password=b123456
filters=stat
initialSize=2
maxActive=300
maxWait=60000
timeBetweenEvictionRunsMillis=60000
minEvictableIdleTimeMillis=300000
validationQuery=SELECT 1
testWhileIdle=true
testOnBorrow=false
testOnReturn=false
poolPreparedStatements=false
maxPoolPreparedStatementPerConnectionSize=200package org.example;
import com.alibaba.druid.pool.DruidDataSource;
import com.alibaba.druid.pool.DruidDataSourceFactory;
import java.io.InputStream;
import java.sql.Connection;
import java.util.Properties;
public class DruidFactory2 {
private static DruidDataSource dataSource = null;
public static void init() throws Exception {
Properties properties = new Properties();
// 加载属性文件 druid.properties
InputStream in = DruidFactory2.class.getClassLoader().getResourceAsStream("druid.properties");
properties.load(in);
// 通过属性创建 Druid 数据源
dataSource = (DruidDataSource) DruidDataSourceFactory.createDataSource(properties);
in.close();
}
public static Connection getConnection() throws Exception {
if (null == dataSource) {
init();
}
return dataSource.getConnection();
}
}
三、基于web的数据库开发
3.1配置DataSource
3.2相关类（driverClassName，驱动类）
3.3Connection接口
java.sql.Connection接口表示与特定数据库的会话。在Connection的上下文中，执行SQL语句并返回结果。Connection接口对于连接到数据库和执行SQL语句至关重要。
3.4Statement接口
Statement接口是Java执行数据库操作的一个重要接口，用于在已经建立数据库连接的基础上，向数据库发送要执行的SQL语句。Statement接口提供了执行语句和获取结果的基本方法。PreparedStatement接口添加了处理IN参数的方法；而CallableStatement添加了处理OUT参数的方法。
3.5PreparedStatement接口
PreparedStatement接口是Java中的一个接口，它是用来执行预编译的SQL语句的。PreparedStatement是Statement的子接口，继承了Statement的所有功能。PreparedStatement接口提供了补充占位符变量的方法
