数据库MySQL（基础六）

15.JDBC (java database connection)

Java数据库连接，（Java Database Connectivity，简称JDBC）是Java语言中用来规范客户端程序如何来访问数据库的应用程序接口，提供了诸如查询和更新数据库中数据的方法。JDBC也是Sun Microsystems的商标。我们通常说的JDBC是面向关系型数据库的。

反射
JDBC的驱动jar包 mysql-connector-java.5.1.49.jar

15.1 Connection （数据库的连接）

A connection (session) with a specific
database. SQL statements are executed and results are returned
within the context of a connection.

数据库连接(会话)，声明数据库连接的信息。连接获取sql语句的执行statement和返回执行的结果。

JDBCUtil.java

package com.shangguan.jdbc.utils;import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;/*** @ClassName: JDBCUtil* @Description: 数据库连接的工具类* @Author: 一尘* @Date: 2020 年 08 月 26 9:27* @Version 1.0*/
public class JDBCUtil {// 数据库连接的驱动private static String  JDBC_DRIVER = "com.mysql.jdbc.Driver";//数据库的urlprivate static String JDBC_URL = "jdbc:mysql://localhost:3306/hello?useSSL=true";//用户名private static String JDBC_USER = "root";//密码private static String JDBC_PASSWORD = "root";//获取数据库连接的方法public static Connection getConnection(){Connection  connection = null;//我们要通过驱动去连接数据库//获取数据库的驱动try {//加载驱动Class.forName(JDBC_DRIVER);//DriverManagerconnection =  DriverManager.getConnection(JDBC_URL,JDBC_USER,JDBC_PASSWORD);//jdk1.7异常链处理} catch (ClassNotFoundException|SQLException e) {e.printStackTrace();}return connection;}public  static  void close(Connection  con, Statement  statement , ResultSet  resultSet){if(con!=null){try {con.close();con=null;} catch (SQLException e) {e.printStackTrace();}}if(statement!=null){try {statement.close();statement=null;} catch (SQLException e) {e.printStackTrace();}}if(resultSet!=null){try {resultSet.close();resultSet=null;} catch (SQLException e) {e.printStackTrace();}}}}

Book.java

package com.shangguan.jdbc.beans;/*** @ClassName: Book* @Description: book* @Author: 一尘* @Date: 2020 年 08 月 26 9:49* @Version 1.0*/
public class Book {//主键private Integer bookId;private String bookName;private String bookAuthor;private double bookPrice;private String bookPublish;private String bookImg;public Book() {}public Book(String bookName, String bookAuthor, double bookPrice, String bookPublish, String bookImg) {this.bookName = bookName;this.bookAuthor = bookAuthor;this.bookPrice = bookPrice;this.bookPublish = bookPublish;this.bookImg = bookImg;}public Book(Integer bookId, String bookName, String bookAuthor, double bookPrice, String bookPublish, String bookImg) {this.bookId = bookId;this.bookName = bookName;this.bookAuthor = bookAuthor;this.bookPrice = bookPrice;this.bookPublish = bookPublish;this.bookImg = bookImg;}public Integer getBookId() {return bookId;}public void setBookId(Integer bookId) {this.bookId = bookId;}public String getBookName() {return bookName;}public void setBookName(String bookName) {this.bookName = bookName;}public String getBookAuthor() {return bookAuthor;}public void setBookAuthor(String bookAuthor) {this.bookAuthor = bookAuthor;}public double getBookPrice() {return bookPrice;}public void setBookPrice(double bookPrice) {this.bookPrice = bookPrice;}public String getBookPublish() {return bookPublish;}public void setBookPublish(String bookPublish) {this.bookPublish = bookPublish;}public String getBookImg() {return bookImg;}public void setBookImg(String bookImg) {this.bookImg = bookImg;}@Overridepublic String toString() {return "Book{" +"bookId=" + bookId +", bookName='" + bookName + '\'' +", bookAuthor='" + bookAuthor + '\'' +", bookPrice=" + bookPrice +", bookPublish='" + bookPublish + '\'' +", bookImg='" + bookImg + '\'' +'}';}
}

BookDao.java

package com.shangguan.jdbc.dao;import com.shangguan.jdbc.beans.Book;import java.util.List;public interface BookDao {//查询所有数据List<Book> queryAll();//根据id查询Book queryById(int bookId);//模糊查询List<Book> queryLikeBookName(String bookName);//添加数据int addBook(Book book);//修改数据int updateBook(Book book);//删除数据int deleteBook(Book book);
}

15.2 Statement

The object used for executing a static SQL statement
and returning the results it produces.

执行静态的Sql语句对象返回结果.静态sql就是定义死的Sql语句。

execute()执行sql语句。

15.3 ResultSet

A table of data representing a database result set, which is usually generated by executing a statement that queries the database.

返回数据库的结果集对象。

package com.shangguan.jdbc.impl;import com.shangguan.jdbc.beans.Book;
import com.shangguan.jdbc.dao.BookDao;
import com.shangguan.jdbc.utils.JDBCUtil;import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;/*** @ClassName: BookDaoImpl* @Description:* @Author: 一尘* @Date: 2020 年 08 月 26 9:56* @Version 1.0*/
public class BookDaoImpl implements BookDao {//获取到数据库的连接Connection  connection = JDBCUtil.getConnection();Statement  statement = null;ResultSet  resultSet = null;@Overridepublic List<Book> queryAll() {List<Book> list = new ArrayList<>();String  sql = "select * from book";try {statement =   connection.createStatement();resultSet = statement.executeQuery(sql);//遍历结果集while(resultSet.next()){Book book = new Book();book.setBookId(resultSet.getInt(1));book.setBookName(resultSet.getString(2));book.setBookAuthor(resultSet.getString(3));book.setBookPrice(resultSet.getDouble(4));book.setBookPublish(resultSet.getString(5));book.setBookImg(resultSet.getString(6));list.add(book);}} catch (SQLException e) {e.printStackTrace();}return list;}@Overridepublic Book queryById(int bookId) {Book  book = null;String sql = "select * from book where bookid = 2 ";try {statement =   connection.createStatement();resultSet = statement.executeQuery(sql);if(resultSet.next()){book = new Book();book.setBookId(resultSet.getInt("bookid"));book.setBookName(resultSet.getString("bookname"));book.setBookAuthor(resultSet.getString("bookauthor"));book.setBookPrice(resultSet.getDouble("bookprice"));book.setBookPublish(resultSet.getString("bookpublish"));book.setBookImg(resultSet.getString("bookimg"));}} catch (SQLException e) {e.printStackTrace();}return book;}@Overridepublic List<Book> queryLikeBookName(String bookName) {List<Book> list = new ArrayList<>();String sql = "select * from book where bookname like concat('%','水浒','%')";try {statement = connection.createStatement();ResultSet resultSet = statement.executeQuery(sql);//遍历结果集while(resultSet.next()){Book book = new Book();book.setBookId(resultSet.getInt(1));book.setBookName(resultSet.getString(2));book.setBookAuthor(resultSet.getString(3));book.setBookPrice(resultSet.getDouble(4));book.setBookPublish(resultSet.getString(5));book.setBookImg(resultSet.getString(6));list.add(book);}} catch (SQLException e) {e.printStackTrace();}return list;}@Overridepublic int addBook(Book book) {int result = 0;String sql = "insert into book values(null,'围城','钱钟书',99.99,'人民出版社','images/1.png')" ;try {statement =  connection.createStatement();result = statement.executeUpdate(sql);} catch (SQLException e) {e.printStackTrace();}return result;}@Overridepublic int updateBook(Book book) {int result = 0;String sql = "update book set bookname = '骆驼祥子',bookauthor='老舍',bookprice=120.00,bookpublish='工业出版社',bookimg='images/2.png' where bookid = 126  ";try {statement =  connection.createStatement();result = statement.executeUpdate(sql);} catch (SQLException e) {e.printStackTrace();}return result;}@Overridepublic int deleteBook(Book book) {int result = 0;String sql = "delete from book where bookid = 126";try {statement = connection.createStatement();result = statement.executeUpdate(sql);} catch (SQLException e) {e.printStackTrace();}return result;}
}

我们发现一些问题:

我们使用的是statement 所以sql语句是静态sql ，数据必须写死不灵活
在resultset中封装数据存在大量重复的代码。在原生的jdbc中必须这样做
封装好的JDBC库,DBUtils

15.4 PreparedStatement(预编译的SQl)

使用?先进行占位
在根据参数的数据类型调用对应的方法设置参数的实际值到参数对应的占位符所在的位置。
参数的下标是从1开始。

package com.shangguan.jdbc.impl;import com.shangguan.jdbc.beans.Book;
import com.shangguan.jdbc.dao.BookDao;
import com.shangguan.jdbc.utils.JDBCUtil;import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;/*** @ClassName: BookDaoImpl2* @Description:* @Author: 一尘* @Date: 2020 年 08 月 26 10:53* @Version 1.0*/
public class BookDaoImpl2 implements BookDao {Connection  connection = JDBCUtil.getConnection();//预编译的SqlPreparedStatement  preparedStatement = null;ResultSet  resultSet = null;@Overridepublic List<Book> queryAll() {List<Book>     list = new ArrayList<>();String sql = "select * from book";try {preparedStatement =   connection.prepareStatement(sql);resultSet =   preparedStatement.executeQuery();while(resultSet.next()){Book     book = new Book();book.setBookId(resultSet.getInt("bookid"));book.setBookName(resultSet.getString("bookname"));book.setBookAuthor(resultSet.getString("bookauthor"));book.setBookPrice(resultSet.getDouble("bookprice"));book.setBookPublish(resultSet.getString("bookpublish"));book.setBookImg(resultSet.getString("bookimg"));list.add(book);}} catch (SQLException e) {e.printStackTrace();}return list;}@Overridepublic Book queryById(int bookId) {Book book = null;//?就是占位符String sql = "select * from book where bookid = ?";try {preparedStatement =     connection.prepareStatement(sql);//将实际的参数设置到坑位上preparedStatement.setInt(1,bookId);resultSet =  preparedStatement.executeQuery();if(resultSet.next()){book = new Book();book.setBookId(resultSet.getInt("bookid"));book.setBookName(resultSet.getString("bookname"));book.setBookAuthor(resultSet.getString("bookauthor"));book.setBookPrice(resultSet.getDouble("bookprice"));book.setBookPublish(resultSet.getString("bookpublish"));book.setBookImg(resultSet.getString("bookimg"));}} catch (SQLException e) {e.printStackTrace();}return book;}@Overridepublic List<Book> queryLikeBookName(String bookName) {List<Book> list = new ArrayList<>();String sql = "select * from book where bookname like concat('%',?,'%')";try {preparedStatement = connection.prepareStatement(sql);preparedStatement.setString(1,bookName);resultSet = preparedStatement.executeQuery();while(resultSet.next()){Book     book = new Book();book.setBookId(resultSet.getInt("bookid"));book.setBookName(resultSet.getString("bookname"));book.setBookAuthor(resultSet.getString("bookauthor"));book.setBookPrice(resultSet.getDouble("bookprice"));book.setBookPublish(resultSet.getString("bookpublish"));book.setBookImg(resultSet.getString("bookimg"));list.add(book);}} catch (SQLException e) {e.printStackTrace();}return list;}@Overridepublic int addBook(Book book) {int  result = 0;String sql = "insert into book values(null,?,?,?,?,?)";try {preparedStatement  = connection.prepareStatement(sql);preparedStatement.setString(1,book.getBookName());preparedStatement.setString(2,book.getBookAuthor());preparedStatement.setDouble(3,book.getBookPrice());preparedStatement.setString(4,book.getBookPublish());preparedStatement.setString(5,book.getBookImg());result  = preparedStatement.executeUpdate();} catch (SQLException e) {e.printStackTrace();}return result;}@Overridepublic int updateBook(Book book) {int result = 0;String sql = "update book set bookname = ?,bookauthor=?,bookprice = ?,bookpublish = ?,bookimg = ? where bookid =  ?";try {preparedStatement  = connection.prepareStatement(sql);preparedStatement.setString(1,book.getBookName());preparedStatement.setString(2,book.getBookAuthor());preparedStatement.setDouble(3,book.getBookPrice());preparedStatement.setString(4,book.getBookPublish());preparedStatement.setString(5,book.getBookImg());preparedStatement.setInt(6,book.getBookId());result = preparedStatement.executeUpdate();} catch (SQLException e) {e.printStackTrace();}return result;}@Overridepublic int deleteBook(Book book) {int result = 0;String sql = "delete from book where bookid = ?";try {preparedStatement = connection.prepareStatement(sql);preparedStatement.setInt(1,book.getBookId());result = preparedStatement.executeUpdate();} catch (SQLException e) {e.printStackTrace();}return result;}
}

15.5 单元测试(JUNIT)

junit 最低是4.12
需要junit的依赖包
- harmcrest-core

package com.shangguan.jdbc.test;import com.shangguan.jdbc.beans.Book;import com.shangguan.jdbc.dao.BookDao;import com.shangguan.jdbc.impl.BookDaoImpl2;import org.junit.Test;import java.util.List;/*** @ClassName: BookTest2* @Description:* @Author: 一尘* @Date: 2020 年 08 月 26 10:57* @Version 1.0*/
public class BookTest2 {BookDao  bookDao = new BookDaoImpl2();@Testpublic  void queryAll(){List<Book> books = bookDao.queryAll();for (Book book : books) {System.out.println(book);}}@Testpublic  void queryById(){System.out.println(bookDao.queryById(11));}@Testpublic  void queryLikeName(){List<Book> list = bookDao.queryLikeBookName("水浒");for (Book book : list) {System.out.println(book);}}@Testpublic  void addBook(){Book book = new Book("被窝是青春的坟墓","七堇年",99.99,"文艺出版社","images/3.jpg");System.out.println(bookDao.addBook(book));}@Testpublic  void updateBook(){Book book = new Book(127,"灯下尘","七堇年",99.99,"文艺出版社","images/3.jpg");System.out.println(bookDao.updateBook(book));}@Testpublic  void deleteBook(){Book book = new Book();book.setBookId(127);System.out.println(bookDao.deleteBook(book));}
}

接口实现类完成以后，里面所有的方法必须先经过单元测试，测试方法的完整性，再在后续的程序中进行调用。

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数据库MySQL（基础六）

15.JDBC (java database connection)

15.1 Connection （数据库的连接）

15.2 Statement

15.3 ResultSet

15.4 PreparedStatement(预编译的SQl)

15.5 单元测试(JUNIT)

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