JDBC——小结

Posted 2020-12-10 小海_macro

基本代码逻辑

Properties properties = new Properties();
String path = BaseDao.class.getClassLoader().getResource("jdbc.properties").getPath();  //maven工程路径问题

【1】加载配置文件

//加载配置文件
properties.load(new FileInputStream(new File(path)));
DRIVER = properties.getProperty("DRIVER");  //获取驱动器完整包名  com.sql.jdbc.driver
URL = properties.getProperty("URL");
USER = properties.getProperty("USER");
PASSWD = properties.getProperty("PASSWD");

【2】加载驱动

Class.forName(DRIVER);

//其本质：registeredDrivers.addIfAbsent(new DriverInfo(driver, da));

【3】获取连接

connection = DriverManager.getConnection(URL, USER, PASSWD);

=================================================

//两种执行方式

    -Statement

Statement statement = connection.createStatement();

【1】查询操作

ResultSet resultSet = statement.executeQuery("select * from emp"
                     + " where empno = "+empno);

while(resultSet.next()){
                 //支持列明，列位置[从1开始]，列别名
                 int eno = resultSet.getInt("empno");

}

    -PreparedStatement：通过设置占位符，避免sql漏洞

PreparedStatement preState = connection.prepareStatement("select * from emp"
                     + " where deptno = ? and job = ?");

preState.setObject(1, deptno);
preState.setString(2, job);
ResultSet resultSet = preState.executeQuery();

【2】插入数据操作

connection = DriverManager.getConnection(url, user, passwd);
PreparedStatement ps = connection.prepareStatement("insert into `dept` values(?,?,?)");
ps.setObject(1, 60);
ps.setObject(2, "Tech_DA");
ps.setObject(3,"Shenzhen");
int i = ps.executeUpdate();  // 返回值>0:擦入数据成功

【3】删除操作

connection = DriverManager.getConnection(url, user, passwd);
PreparedStatement ps = connection.prepareStatement("delete from `dept` where `deptno` = ?");
ps.setObject(1, 60);
int i = ps.executeUpdate();

【4】更新数据

connection = DriverManager.getConnection(url, user, passwd);
PreparedStatement ps = connection.prepareStatement("update dept set dname = ? where deptno = 60");
ps.setObject(1, "DataCenter");
int i = ps.executeUpdate();

【5】批量添加

PreparedStatement ps = connection.prepareStatement("insert into `dept` values(?,?,?)");
for(int dept=50;dept<100;dept+=10){
     ps.setObject(1, dept);
     ps.setObject(2, "Product");
     ps.setObject(3,"beijing");
    ps.addBatch();
}
int[] flags = ps.executeBatch();

【6】数据提交

connection.setAutoCommit(false);  //设置取消自动提交
PreparedStatement ps = connection.prepareStatement("insert into `dept` values(?,?,?)");
ps.setObject(1, 60);
ps.setObject(2, "Tech_DA");
ps.setObject(3,"Shenzhen");
int i = ps.executeUpdate();  //执行sql语句
System.out.println(i);
if (i==1) {
     int res = 1/0;
     connection.commit();  //提交
}

进一步封装查询

-queryScottBypar()

StringBuilder sql = new StringBuilder();  // 存放操作指令字符串
sql.append("select deptno , dname, loc from dept where 1=1 ");
//动态组装，添加条件
if (dept!=null) {
     if (dept.getDeptno()!=null) {
         sql.append(" and deptno = ?");
     }

}

ps = con.prepareStatement(sql.toString());

if (dept!=null) {
     if (dept.getDeptno()!=null) {
         ps.setObject(++index, dept.getDeptno());
     }

}

添加对应得jar包  &&  maven依赖

<dependency>
     <groupId>mysql</groupId>
     <artifactId>mysql-connector-java</artifactId>
     <version>5.1.48</version>
</dependency>

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