java jdbc连接和使用
jdbc
导入驱动
//jar是已经打包好的class文件集，可以引用到其他工程中
//Build Path中add external jars导入
连接JDBC
1. 加载驱动
Class.from("com.mysql.jdbc.Driver");
创建连接
//导包使用 java.sql.*； String jdbc="jdbc:mysql://localhost:3306/student?user=root&password=&characterEncoding=utf-8";//student是表名 Connection conn = DriverManager.getConnection(jdbc);
2. 注意 数据库打开之后一定要记得关。
conn.close();
1. 执行SQL语句 （创建表，插入，删除，更新）
使用Statemant
Statemant st = conn.createStatemant(); int row = st.executeUpdate(sql语句);//不能做查询操作。
使用PrepareStatement
可以使用？占位符来代替你需要传递的参数
String sql = "insert into " + TABLENAME + "(name,subject,score) values(?,?,?)"; PrepareStatement pt = conn.prepareStatement(sql); //给每一位占位符设置值,下标从1开始 pt.setString(1,score.getName()); pt.setString(2.score.getSubject()); pt.setDouble(3,score.getScore()); //使用无参的方法 pt.executeUpdate();
1.查询操作
static List<Score> queryScore(Connection pconn, Score pScore)
throws SQLException {
ArrayList<Score> mlist = new ArrayList<>();
String sql = "select * from " + TABLENAME + " where name = ?";
PreparedStatement ps = pconn.prepareStatement(sql);
ps.setString(1, pScore.getName());
ResultSet rs = ps.executeQuery();
while (rs.next()) {
// 这里可以通过rs获取所有结果
String subject = rs.getString("subject");
int id = rs.getInt("id");
double score = rs.getDouble("score");
mlist.add(new Score(id, pScore.getName(), subject, score));
}
return mlist;
}
下面是一个小程序
//建立数据库连接类
public class DAO {
// 放问数据库的链接地址
static String jdbc = "jdbc:mysql://localhost:3306/student?user=root&password=&characterEncoding=utf-8";
// 打开链接
public static Connection connection() {
// 使用JDBC的步骤
// 1. 加载JDBC驱动
try {
// 类的全名 包名+类名
Class.forName("com.mysql.jdbc.Driver");
// 2. 连接数据库
Connection conn = DriverManager.getConnection(jdbc);
return conn;
} catch (Exception e) {
System.out.println("驱动加载失败");
return null;
}
}
}
//分数类
public class Score {
String name;
String id;
String subject;
double score;
public Score(String name, String subject, double score) {
super();
this.name = name;
this.subject = subject;
this.score = score;
}
@Override
public String toString() {
return "Score [name=" + name + ", id=" + id + ", subject=" + subject
+ ", score=" + score + "]";
}
public Score(String name, String id, String subject, double score) {
super();
this.name = name;
this.id = id;
this.subject = subject;
this.score = score;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getSubject() {
return subject;
}
public void setSubject(String subject) {
this.subject = subject;
}
public double getScore() {
return score;
}
public void setScore(double score) {
this.score = score;
}
}
//实现类
public class Test {
public static String TABLENAME = "score";
public static void main(String[] args) {
try {
Connection conn = DAO.connection();
if (conn != null) {
System.out.println("链接上了");
// createTable(conn);
// 插入一条记录
// Score score = new Score("李四 ", "Android", 98);
// System.out.println(addScore2(conn, score));
// deleteScore(conn, score);
// updateScore(conn, score);
List<Score> list = queryScoreByName(conn, "王五"); //queryAllScore(conn);
for (Score score : list) {
System.out.println(score);
}
conn.close();
} else {
System.out.println("链接失败 ");
}
} catch (SQLException e) {
e.printStackTrace();
}
}
// 创建一张表
public static boolean createTable(Connection conn) {
// 开始执行sql语句
String sql = "create table "
+ TABLENAME
+ "(id integer primary key auto_increment,name varchar(3) not null,subject varchar(20) not null,score double)";
// 要执行一条语句，需要一个执行的类 Statement
try {
Statement st = conn.createStatement();
int result = st.executeUpdate(sql);
System.out.println(result);
if (result != -1)
return true;
} catch (SQLException e) {
e.printStackTrace();
}
return false;
}
// 添加一条记录
public static boolean addScore(Connection conn, Score score)
throws SQLException {
String sql = "insert into " + TABLENAME
+ "(name,subject,score) values('" + score.getName() + "','"
+ score.getSubject() + "'," + score.getScore() + ")";
System.out.println(sql);
Statement st = conn.createStatement();
int row = st.executeUpdate(sql);
if (row > 0)
return true;
return false;
}
// 添加一条记录2
public static boolean addScore2(Connection conn, Score score)
throws SQLException {
// 占位符?来代替需要设置的参数
String sql = "insert into " + TABLENAME
+ "(name,subject,score) values(?,?,?)";
PreparedStatement ps = conn.prepareStatement(sql);
// 必须给定？所代表的值
ps.setString(1, score.getName());
ps.setString(2, score.getSubject());
ps.setDouble(3, score.getScore());
// 调用无参的方法
int row = ps.executeUpdate();
if (row > 0)
return true;
return false;
}
public static boolean deleteScore(Connection conn, Score score)
throws SQLException {
String sql = "delete from " + TABLENAME + " where name=? and subject=?";
// 创建PrepareStatement
PreparedStatement ps = conn.prepareStatement(sql);
ps.setString(1, score.getName());
ps.setString(2, score.getSubject());
// ps.setDouble(3, score.getScore());
// 执行
int row = ps.executeUpdate();
System.out.println(row);
if (row > 0)
return true;
return false;
}
public static boolean updateScore(Connection conn, Score score)
throws SQLException {
// 修改 score人他的科目的成绩
String sql = "update " + TABLENAME
+ " set score=? where name=? and subject=?";
PreparedStatement ps = conn.prepareStatement(sql);
ps.setDouble(1, score.getScore());
ps.setString(2, score.getName());
ps.setString(3, score.getSubject());
int row = ps.executeUpdate();
System.out.println(row);
if (row > 0)
return true;
return false;
}
public static List<Score> queryAllScore(Connection conn)
throws SQLException {
String sql = "select * from " + TABLENAME;
// 开始查询
Statement st = conn.createStatement();
ResultSet rs = st.executeQuery(sql);
List<Score> list = new ArrayList<Score>();
while (rs.next()) {
// 这里可以通过rs获取所有结果
String id = rs.getString("id");
String name = rs.getString("name");
String subject = rs.getString("subject");
double score = rs.getDouble("score");
list.add(new Score(name, id, subject, score));
}
// 结束
return list;
}
public static List<Score> queryScoreByName(Connection conn, String name)
throws SQLException {
String sql = "select * from " + TABLENAME + " where name=?";
PreparedStatement pt = conn.prepareStatement(sql);
pt.setString(1, name);
ResultSet rs = pt.executeQuery();
List<Score> list = new ArrayList<>();
while (rs.next()) {
String subject = rs.getString("subject");
String id = rs.getString("id");
double score = rs.getDouble("score");
list.add(new Score(name, id, subject, score));
}
return list;
}
