Detailed introduction to java jdbc connection and use

java jdbc connection and use

jdbc

Import driver

//jar is a packaged set of class files that can be referenced in other projects
//Add external jars import in Build Path

Connect to JDBC

1. Load driver

Class.from("com.mysql.jdbc.Driver");

Create connection

//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. Note that you must remember to close the database after opening it.

conn.close();

1. Execute SQL statements (create table, insert, delete, update)

Use Statemant

Statemant st = conn.createStatemant();
 int row = st.executeUpdate(sql语句);//不能做查询操作。

Use Can PrepareStatement

be used? Placeholders to replace the parameters you need to pass

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. Query operation

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;
  }

The following is a small program

//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(&#39;" + score.getName() + "&#39;,&#39;"
        + score.getSubject() + "&#39;," + 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;
  }

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