tags: JDBC

1.PreparedStatement对象

PreparedStatement对象继承Statement对象，它比Statement对象更强大，使用起来更简单

1. Statement对象编译SQL语句时，如果SQL语句有变量，就需要使用分隔符来隔开，如果变量非常多，就会使SQL变得非常复杂。PreparedStatement可以使用占位符，简化sql的编写
2. Statement会频繁编译SQL。PreparedStatement可对SQL进行预编译，提高效率，预编译的SQL存储在PreparedStatement对象中
3. PreparedStatement防止SQL注入。【Statement通过分隔符'++',编写永等式，可以不需要密码就进入数据库】

//模拟查询id为2的信息String id = "2";Connection connection = UtilsDemo.getConnection();String sql = "SELECT * FROM users WHERE id = ?";PreparedStatement preparedStatement = connection.preparedStatement(sql);//第一个参数表示第几个占位符【也就是?号】，第二个参数表示值是多少preparedStatement.setString(1,id);ResultSet resultSet = preparedStatement.executeQuery();if (resultSet.next()) {System.out.println(resultSet.getString("name"));}//释放资源UtilsDemo.release(connection, preparedStatement, resultSet);复制代码

2.批处理

当需要向数据库发送一批SQL语句执行时，应避免向数据库一条条发送执行，采用批处理以提升执行效率

批处理有两种方式：

1. Statement
2. PreparedStatement

通过executeBath()方法批量处理执行SQL语句，返回一个int[]数组，该数组代表各句SQL的返回值

以下代码是以Statement方式实现批处理

/** Statement执行批处理** 优点：*       可以向数据库发送不同的SQL语句* 缺点：*       SQL没有预编译*       仅参数不同的SQL，需要重复写多条SQL* */Connection connection = UtilsDemo.getConnection();Statement statement = connection.createStatement();String sql1 = "UPDATE users SET name='zhongfucheng' WHERE id='3'";String sql2 = "INSERT INTO users (id, name, password, email, birthday)" +" VALUES('5','nihao','123','ss@qq.com','1995-12-1')";//将sql添加到批处理statement.addBatch(sql1);statement.addBatch(sql2);//执行批处理statement.executeBatch();//清空批处理的sqlstatement.clearBatch();UtilsDemo.release(connection, statement, null);复制代码

以下方式以PreparedStatement方式实现批处理

/** PreparedStatement批处理*   优点：*       SQL语句预编译了*       对于同一种类型的SQL语句，不用编写很多条*   缺点：*       不能发送不同类型的SQL语句** */Connection connection = UtilsDemo.getConnection();String sql = "INSERT INTO test(id,name) VALUES (?,?)";PreparedStatement preparedStatement = connection.prepareStatement(sql);for (int i = 1; i <= 205; i++) {preparedStatement.setInt(1, i);preparedStatement.setString(2, (i + "zhongfucheng"));//添加到批处理中preparedStatement.addBatch();if (i %2 ==100) {//执行批处理preparedStatement.executeBatch();//清空批处理【如果数据量太大，所有数据存入批处理，内存肯定溢出】preparedStatement.clearBatch();}}//不是所有的%2==100，剩下的再执行一次批处理preparedStatement.executeBatch();//再清空preparedStatement.clearBatch();UtilsDemo.release(connection, preparedStatement, null);复制代码

3.处理大文本和二进制数据

clob和blob

• clob用于存储大文本
• blob用于存储二进制数据

MYSQL

MySQL存储大文本是用Test【代替clob】，Test又分为4类

• TINYTEXT
• TEXT
• MEDIUMTEXT
• LONGTEXT

同理blob也有这4类

下面用JDBC连接MySQL数据库去操作大文本数据和二进制数据

/*
*用JDBC操作MySQL数据库去操作大文本数据
*
*setCharacterStream(int parameterIndex,java.io.Reader reader,long length)
*第二个参数接收的是一个流对象，因为大文本不应该用String来接收，String太大会导致内存溢出
*第三个参数接收的是文件的大小
*
* */
public class Demo5 {@Testpublic void add() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();String sql = "INSERT INTO test2 (bigTest) VALUES(?) ";preparedStatement = connection.prepareStatement(sql);//获取到文件的路径String path = Demo5.class.getClassLoader().getResource("BigTest").getPath();File file = new File(path);FileReader fileReader = new FileReader(file);//第三个参数，由于测试的Mysql版本过低，所以只能用int类型的。高版本的不需要进行强转preparedStatement.setCharacterStream(1, fileReader, (int) file.length());if (preparedStatement.executeUpdate() > 0) {System.out.println("插入成功");}} catch (SQLException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} finally {JdbcUtils.release(connection, preparedStatement, null);}}/** 读取大文本数据，通过ResultSet中的getCharacterStream()获取流对象数据* * */@Testpublic void read() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();String sql = "SELECT * FROM test2";preparedStatement = connection.prepareStatement(sql);resultSet = preparedStatement.executeQuery();if (resultSet.next()) {Reader reader = resultSet.getCharacterStream("bigTest");FileWriter fileWriter = new FileWriter("d:\\abc.txt");char[] chars = new char[1024];int len = 0;while ((len = reader.read(chars)) != -1) {fileWriter.write(chars, 0, len);fileWriter.flush();}fileWriter.close();reader.close();}} catch (SQLException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {JdbcUtils.release(connection, preparedStatement, resultSet);}}复制代码

/*
* 使用JDBC连接MYsql数据库操作二进制数据
* 如果我们要用数据库存储一个大视频的时候，数据库是存储不到的。
* 需要设置max_allowed_packet，一般我们不使用数据库去存储一个视频
* */
public class Demo6 {@Testpublic void add() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();String sql = "INSERT INTO test3 (blobtest) VALUES(?)";preparedStatement = connection.prepareStatement(sql);//获取文件的路径和文件对象String path = Demo6.class.getClassLoader().getResource("1.wmv").getPath();File file = new File(path);//调用方法preparedStatement.setBinaryStream(1, new FileInputStream(path), (int)file.length());if (preparedStatement.executeUpdate() > 0) {System.out.println("添加成功");}} catch (SQLException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} finally {JdbcUtils.release(connection, preparedStatement, null);}}@Testpublic void read() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();String sql = "SELECT * FROM test3";preparedStatement = connection.prepareStatement(sql);resultSet = preparedStatement.executeQuery();//如果读取到数据，就把数据写到磁盘下if (resultSet.next()) {InputStream inputStream = resultSet.getBinaryStream("blobtest");FileOutputStream fileOutputStream = new FileOutputStream("d:\\aa.jpg");int len = 0;byte[] bytes = new byte[1024];while ((len = inputStream.read(bytes)) > 0) {fileOutputStream.write(bytes, 0, len);}fileOutputStream.close();inputStream.close();}} catch (SQLException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {JdbcUtils.release(connection, preparedStatement, null);}}复制代码

Oracle

下面用JDBC连接Oracle数据库去操作大文本数据和二进制数据

//使用JDBC连接Oracle数据库操作二进制数据/*
* 对于Oracle数据库和Mysql数据库是有所不同的。
* 1.Oracle定义了BLOB字段，但是这个字段不是真正地存储二进制数据
* 2.向这个字段存一个BLOB指针，获取到Oracle的BLOB对象,把二进制数据放到这个指针里面,指针指向BLOB字段
* 3.需要事务支持
*
* */
public class Demo7 {@Testpublic void add() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = UtilsDemo.getConnection();//开启事务connection.setAutoCommit(false);//插入一个BLOB指针String sql = "insert into test4(id,image) values(?,empty_blob())";preparedStatement = connection.prepareStatement(sql);preparedStatement.setInt(1, 1);preparedStatement.executeUpdate();//把BLOB指针查询出来,得到BLOB对象String sql2 = "select image from test4 where id= ? for update";preparedStatement = connection.prepareStatement(sql2);preparedStatement.setInt(1, 1);resultSet = preparedStatement.executeQuery();if (resultSet.next()) {//得到Blob对象--当成是Oracle的Blob,不是JDBC的,所以要强转[导的是oracle.sql.BLOB包]BLOB  blob = (BLOB) resultSet.getBlob("image");//写入二进制数据OutputStream outputStream = blob.getBinaryOutputStream();//获取到读取文件读入流InputStream inputStream = Demo7.class.getClassLoader().getResourceAsStream("01.jpg");int len=0;byte[] bytes = new byte[1024];while ((len = inputStream.read(bytes)) > 0) {outputStream.write(bytes, 0, len);}outputStream.close();inputStream.close();connection.setAutoCommit(true);}} catch (SQLException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {UtilsDemo.release(connection, preparedStatement, null);}}@Testpublic void find() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = UtilsDemo.getConnection();String sql = "SELECT * FROM test4 WHERE id=1";preparedStatement = connection.prepareStatement(sql);resultSet = preparedStatement.executeQuery();if (resultSet.next()) {//获取到BLOB对象BLOB blob = (BLOB) resultSet.getBlob("image");//将数据读取到磁盘上InputStream inputStream = blob.getBinaryStream();FileOutputStream fileOutputStream = new FileOutputStream("d:\\zhongfucheng.jpg");int len=0;byte[] bytes = new byte[1024];while ((len = inputStream.read(bytes)) > 0) {fileOutputStream.write(bytes, 0, len);}inputStream.close();fileOutputStream.close();}} catch (SQLException e) {e.printStackTrace();} catch (FileNotFoundException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();} finally {UtilsDemo.release(connection, preparedStatement, null);}}
}复制代码

对于JDBC连接Oracle数据库操作CLOB数据,我就不再重复了,操作跟BLOB几乎相同

4.获取数据库的自动主键列

为什么要获取数据库的自动主键列数据?

应用场景:

有一张老师表，一张学生表。现在来了一个新的老师，学生要跟着新老师上课。

我首先要知道老师的id编号是多少，学生才能知道跟着哪个老师学习【学生外键参照老师主键】。

@Testpublic void test() {Connection connection = null;PreparedStatement preparedStatement = null;ResultSet resultSet = null;try {connection = JdbcUtils.getConnection();String sql = "INSERT INTO test(name) VALUES(?)";preparedStatement = connection.prepareStatement(sql);preparedStatement.setString(1, "ouzicheng");if (preparedStatement.executeUpdate() > 0) {//获取到自动主键列的值resultSet = preparedStatement.getGeneratedKeys();if (resultSet.next()) {int id = resultSet.getInt(1);System.out.println(id);}}} catch (SQLException e) {e.printStackTrace();} finally {JdbcUtils.release(connection, preparedStatement, null);}复制代码

5.调用数据库的存储过程

调用存储过程的语法：

{call <procedure-name>[(<arg1>,<arg2>, ...)]}
复制代码

调用函数的语法：

{?= call <procedure-name>[(<arg1>,<arg2>, ...)]}
复制代码

如果是Output类型的，那么在JDBC调用的时候是要注册的。如下代码所示：

/*jdbc调用存储过程delimiter $$CREATE PROCEDURE demoSp(IN inputParam VARCHAR(255), INOUT inOutParam varchar(255))BEGINSELECT CONCAT('zyxw---', inputParam) into inOutParam;END $$delimiter ;
*/
//我们在JDBC调用存储过程,就像在调用方法一样
public class Demo9 {public static void main(String[] args) {Connection connection = null;CallableStatement callableStatement = null;try {connection = JdbcUtils.getConnection();callableStatement = connection.prepareCall("{call demoSp(?,?)}");callableStatement.setString(1, "nihaoa");//注册第2个参数,类型是VARCHARcallableStatement.registerOutParameter(2, Types.VARCHAR);callableStatement.execute();//获取传出参数[获取存储过程里的值]String result = callableStatement.getString(2);System.out.println(result);} catch (Exception e) {e.printStackTrace();}finally {try {connection.close();callableStatement.close();} catch (SQLException e) {e.printStackTrace();}}}复制代码

参考资料：

----------------------------------------------------------------------------------过程#修改mysql语句的结果符为//
mysql > delimiter //#定义一个过程，获取users表总记录数，将10设置到变量count中
create procedure simpleproc(out count int)
beginselect count(id) into count from users;
end
//#修改mysql语句的结果符为;
mysql > delimiter ;#调用过程，将结果覆给变量a，@是定义变量的符号
call simpleproc(@a);#显示变量a的值
select @a;//以下是Java调用Mysql的过程String sql = "{call simpleproc(?)}";Connection conn = JdbcUtil.getConnection();CallableStatement cstmt = conn.prepareCall(sql);cstmt.registerOutParameter(1,Types.INTEGER);cstmt.execute();Integer count = cstmt.getInt(1);System.out.println("共有" + count + "人");----------------------------------------------------------------------------------函数#修改mysql语句的结果符为//
mysql > delimiter //#定义一个函数，完成字符串拼接
create function hello( s char(20) ) returns char(50)
return concat('hello，',s,'!');
//#修改mysql语句的结果符为;
mysql > delimiter ;#调用函数
select hello('world');//以下是Java调用Mysql的函数String sql = "{? = call hello(?)}";Connection conn = JdbcUtil.getConnection();CallableStatement cstmt = conn.prepareCall(sql);cstmt.registerOutParameter(1,Types.VARCHAR);cstmt.setString(2,"zhaojun");cstmt.execute();String value = cstmt.getString(1);System.out.println(value);JdbcUtil.close(cstmt);JdbcUtil.close(conn);复制代码

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