java JDBC

数据库URL

JDBC URL的一般语法为: jdbc:subprotocol:other stufff

其中,suprotocol 用于选择连接到数据库的具体驱动程序,  other stuff 参数的格式随所使用的subprotocol的不同而不同

例如:

jdbc:derby://localhost:1527//COREJAVA;ctreate=true

jdbc:postgresql:COREJAVA      // postgresql 和derby是数据库

驱动程序JAR文件:

驱动文件可以在数据库的官网下载;例如mysql的驱动程序下载地址

也可以创建MAVEN项目

在:https://dev.mysql.com/downloads/connector/  选择对应压缩包下载

命令行连接:https://www.cnblogs.com/jiangfeilong/p/10587376.html

maven  JDBC连接实例

package org.feilong.mysql;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
//import com.mysql.cj.jdbc.*;

public class Url {
    public static final String URL = "jdbc:mysql://192.168.1.104:3306/gc";
    public static final String USER = "root";
    public static final String PASSWORD = "1";

    public static void main(String[] args) {
            try {
                Class.forName("com.mysql.cj.jdbc.Driver");
                System.out.println("register success");
            } catch (ClassNotFoundException e1) {
                System.out.println("register fail");
                e1.printStackTrace();
            }//注册驱动
            
            try(Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)){//连接
            Statement stmt = conn.createStatement();  //执行者
            ResultSet rs = stmt.executeQuery("SELECT * FROM books"); //结果集, 
                                         //
                while (rs.next()) {
                    System.out.println(rs.getString("author") + " "+rs.getString(2));
                }
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            
    }
}

public ResultSet executeQuery()执行select语句 返回结果在result里

public int executeUpdate()
public long executelargeUpdate()
执行Insert/update/delete/create table/drop table等 返回修改的行数

public boolean execute() 执行任何语句

ReultSet使用注意事项:

得到数据库信息

try(Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)){//连接
            Statement stmt = conn.createStatement();  //执行者
            //Integer rs = stmt.executeUpdate("DROP DATABASE IF EXISTS mysql_test1"); 
            DatabaseMetaData meta = conn.getMetaData();
            ResultSet rs1 = meta.getCatalogs();
            while(rs1.next())
                System.out.println(rs1.getString(1));
                conn.close();

事务处理

JDBC 事务步骤

关闭自动提交,实现多语句同一事务

 connection.setAutoCommit(false);

connection.commit();提交事务

connection.rollback();回滚事务

保存点机制

　　connection.setSavepoint()

　　connection.rollback(savepoint)

public static void execute(Connection conn,String sql){
        try {
            Statement stmt = conn.createStatement();
            boolean rs = stmt.execute(sql);
            
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
    }
    public static void main(String[] args) {
            try {
                Class.forName("com.mysql.cj.jdbc.Driver");
                System.out.println("register success");
            } catch (ClassNotFoundException e1) {
                System.out.println("register fail");
                e1.printStackTrace();
            }//注册驱动
            
            try(Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)){//连接
                conn.setAutoCommit(false); //关闭自动提交
                
            
                    execute(conn,"USE mysql_test");  
                   // PreparedStatement pstmt = conn.prepareStatement(sql);
                  //pstmt.setString(1,"cust_id INT NOT NULL AUTO_INCREMENT,");
                    
                    String sql = "CREATE TABLE customers ( ?,?,?,?,?,?)";                
                    execute(conn,"CREATE TABLE customers" + 
                    "(" + 
                    "cust_id INT NOT NULL AUTO_INCREMENT, " + //#INCREMENT 可以为表中的数据类型为整形的列设置自增型 
                    "cust_name CHAR(50) NOT NULL,        "  + //#不允许null值的列  
                    "cust_set CHAR(1) NOT NULL DEFAULT 0, " + //不允许null值的列且默认值是0 
                    "cust_address CHAR(50) NULL," + 
                    "cust_contact CHAR(50) NULL," + 
                    "PRIMARY KEY(cust_id)  " +    //设置cust_id 为主键 
                    ")"); 
                    Savepoint phase1 = conn.setSavepoint(); //设置一个保存点
                    execute(conn,"SHOW TABLES");
                    conn.rollback(phase1); //回到保存点 即上面2行无效
                    conn.commit(); //执行操作
                    System.out.println("success");
            //DatabaseMetaData meta = conn.getMetaData();
            //ResultSet rs1 = meta.getCatalogs();
            //while(rs.next())
                //System.out.println(rs.getString(1));
                conn.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

 安全的字符串拼接PreparedStatement 

普通的字符串拼接可能会被人加入恶意代码,使用PreparedStatement可以避免

 PreparedStatement采用待定系数法,使用示例

 String sql = "INSERT INTO customers VALUES( ?,?,?,?,?)";
                    PreparedStatement pstmt = conn.prepareStatement(sql);
                    pstmt.setInt(1,1);  //替换sql里的?号
                    pstmt.setString(2, "feilong");
                    pstmt.setString(3, "1");
                    pstmt.setString(4, "www.feilong.com");
                    pstmt.setString(5, "china");
                    int rs = pstmt.executeUpdate();
                    Savepoint phase1 = conn.setSavepoint(); //设置一个保存点
                    execute(conn,"SHOW TABLES");
                    conn.rollback(phase1); //回到保存点 即上面2行无效
                    conn.commit(); //执行操作
                    System.out.println("success");

 PreparedStatement有一个 Batch方法可以批量提交

try(Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)){//连接
                conn.setAutoCommit(false); //关闭自动提交
                
            
                    execute(conn,"USE mysql_test");  
                   
                  //pstmt.setString(1,"cust_id INT NOT NULL AUTO_INCREMENT,");
                    
                    String sql = "INSERT INTO customers VALUES( ?,?,?,?,?)";
                    PreparedStatement pstmt = conn.prepareStatement(sql);
                    for(int i = 2; i < 100; i++){
                    pstmt.setInt(1,i);  //替换sql里的?号
                    pstmt.setString(2, "feilong");
                    pstmt.setString(3, "1");
                    pstmt.setString(4, "www.feilong.com");
                    pstmt.setString(5, "china");
                    pstmt.addBatch(); //添加到batch列表
                    }
                   // int rs = pstmt.executeUpdate();
                    pstmt.executeBatch(); //全部提交
                    //pstmt.close();
                   Savepoint phase1 = conn.setSavepoint(); //设置一个保存点
                   execute(conn,"SHOW TABLES");
                   conn.rollback(phase1); //回到保存点 即上面2行无效
                   conn.commit(); //执行操作
                    System.out.println("success");

ResultSetMetaData

ResultSet可以用来承载所有的select语句返回的结果集

ResultSetmetaData用来获取ResultSet返回的属性(如,没一行的名字类型等)

示例:

try (Connection conn = DriverManager.getConnection(URL, USER, PASSWORD)) {// 连接
            conn.setAutoCommit(false); // 关闭自动提交
            execute(conn, "USE mysql_test");
            Statement stmt = conn.createStatement();
            ResultSet rs   = stmt.executeQuery("SELECT * FROM customers");
            ResultSetMetaData meta = rs.getMetaData(); //得到元数据
            int cols = meta.getColumnCount(); //得到列的数量
            for(int i = 1; i <= cols; i++){
                System.out.println(meta.getColumnName(i) + "," + meta.getColumnTypeName(i));;
            }
            // pstmt.close();
            Savepoint phase1 = conn.setSavepoint(); // 设置一个保存点
            execute(conn, "SHOW TABLES");
            conn.rollback(phase1); // 回到保存点 即上面2行无效
            conn.commit(); // 执行操作
            System.out.println("success");
            // DatabaseMetaData meta = conn.getMetaData();
            // ResultSet rs1 = meta.getCatalogs();
            // while(rs.next())
            // System.out.println(rs.getString(1));
            conn.close();

数据库连接池

享元模式

 

 C3P0连接池

 

//C3p0连接池
package org.feilong.mysql;

import java.sql.Connection;
import com.mchange.v2.c3p0.ComboPooledDataSource;

public class C3p0Factory1 {
    private static ComboPooledDataSource dataSource = null;
    
    public static void init() throws Exception{
        dataSource = new ComboPooledDataSource();
        dataSource.setDriverClass("com.mysql.cj.jdbc.Driver"); //加载驱动
        dataSource.setJdbcUrl("jdbc:mysql://192.168.1.104:3306/mysql_test"); //数据库URL
        dataSource.setUser("root"); //设置帐号
        dataSource.setPassword("1"); //设置密码
        
        dataSource.setMinPoolSize(5); //设置初始连接数量
        dataSource.setAcquireIncrement(5); //设置每次增加的数量
        dataSource.setMaxPoolSize(20);  //设置最大连接数量
    }

public static Connection getConnection() throws Exception{
    if(dataSource == null){
        init();
    }
    return dataSource.getConnection(); //连接数据库
}
}

Druid和加载properies连接示例

package org.feilong.mysql;

import com.alibaba.druid.pool.DruidDataSourceFactory;

import java.io.InputStream;
import java.sql.Connection;
import java.util.Properties;

import com.alibaba.druid.pool.DruidDataSource;

public class DruidFactory1 {
    private static DruidDataSource dataSource = null;
    
    public static void init() throws Exception
    {
        Properties properties = new Properties(); //Properties 配置参数文件
        
        InputStream in = DruidFactory1.class.getClassLoader().getResourceAsStream("druid.properties");
        properties.load(in);
        dataSource = (DruidDataSource)DruidDataSourceFactory.createDataSource(properties);
        
        in.close();
    }
    public static Connection getConnection() throws Exception{
        if( dataSource == null)
        {
            init();
        }
        return dataSource.getConnection();
    }
}

package org.feilong.mysql;

import java.sql.*;

import javax.sql.rowset.CachedRowSet;
import javax.sql.rowset.RowSetFactory;
import javax.sql.rowset.RowSetProvider;

public class SelectTest {
    public static void main(String[] args) {
        Connection conn = null;
        try {
            conn = DruidFactory1.getConnection();
            Statement stmt = conn.createStatement();
            System.out.println("create success");
            ResultSet rs = stmt.executeQuery("SELECT * FROM mysql_test.customer ORDER BY cust_address");
            
                while (rs.next()) {
                    System.out.println(rs.getRow()+", " +rs.getString(1) + ", " + rs.getString(2));
                }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            try {
                if (conn != null)
                    conn.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }
}

properties配置文件

driverClassName=com.mysql.jdbc.Driver
url=jdbc:mysql://127.0.0.1:3306/test
username=root
password=123456
filters=stat
initialSize=2
maxActive=300
maxWait=60000
timeBetweenEvictionRunsMillis=60000
minEvictableIdleTimeMillis=300000
validationQuery=SELECT 1
testWhileIdle=true
testOnBorrow=false
testOnReturn=false
poolPreparedStatements=false
maxPoolPreparedStatementPerConnectionSize=200