java jdbc connection and use details

java jdbc connect and use

jdbc

The import drivers

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

Connection JDBC

1. Load the driver

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

Create a connection

// Guide package use  java.sql.* ; 
String jdbc="jdbc:mysql://localhost:3306/student?user=root&password=&characterEncoding=utf-8";//student Is the name of the table 
Connection conn = DriverManager.getConnection(jdbc);

2. Remember to close 1 after the database is opened.

 conn.close();

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

Using Statemant

Statemant st = conn.createStatemant();
 int row = st.executeUpdate(sql statements );// Cannot do query operation. 

Using PrepareStatement

Can you use it? Placeholders to replace the arguments you need to pass

String sql = "insert into " + TABLENAME
+ "(name,subject,score) values(?,?,?)";
PrepareStatement pt = conn.prepareStatement(sql);
 // For each 1 The bit holder sets the value , The subscript from 1 start 
 pt.setString(1,score.getName());
 pt.setString(2.score.getSubject());
pt.setDouble(3,score.getScore());
 // Use the method without arguments 
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()) {
      //  Here you can go through rs Get all the results 
      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;
  }

Here is a small program

// Create a database connection class 
public class DAO {

  //  Ask the link address of the database 
  static String jdbc = "jdbc:mysql://localhost:3306/student?user=root&password=&characterEncoding=utf-8";

  //  Open the link 
  public static Connection connection() {
    //  use JDBC The steps of 
    // 1.  loading JDBC drive 
    try {
      //  The full name of a class   The package name + The name of the class 
      Class.forName("com.mysql.jdbc.Driver");
      // 2.  Connect to database 
      Connection conn = DriverManager.getConnection(jdbc);
      return conn;
    } catch (Exception e) {
      System.out.println(" Driver load failed ");
      return null;
    }
  }



}


// Grade class 
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;
  }

}


// The implementation class 
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(" Link on the ");
        // createTable(conn);
        //  insert 1 records 
        // Score score = new Score(" li 4 ", "Android", 98);
        // System.out.println(addScore2(conn, score));
        // deleteScore(conn, score);
        // updateScore(conn, score);
        List<Score> list = queryScoreByName(conn, " The king 5"); //queryAllScore(conn);
        for (Score score : list) {
          System.out.println(score);
        }
        conn.close();
      } else {
        System.out.println(" A link failure  ");
      }
    } catch (SQLException e) {
      e.printStackTrace();
    }
  }

  //  create 1 table 
  public static boolean createTable(Connection conn) {
    //  Start to perform sql statements 
    String sql = "create table "
        + TABLENAME
        + "(id integer primary key auto_increment,name varchar(3) not null,subject varchar(20) not null,score double)";
    //  To perform 1 Statement, yes 1 Class for execution  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;
  }

  //  add 1 records 
  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;
  }

  //  add 1 records 2
  public static boolean addScore2(Connection conn, Score score)
      throws SQLException {
    //  A placeholder ? In place of the parameters that need to be set 
    String sql = "insert into " + TABLENAME
        + "(name,subject,score) values(?,?,?)";
    PreparedStatement ps = conn.prepareStatement(sql);
    //  Must be given? The value represented 
    ps.setString(1, score.getName());
    ps.setString(2, score.getSubject());
    ps.setDouble(3, score.getScore());
    //  Calls a method with no arguments 
    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=?";
    //  create PrepareStatement
    PreparedStatement ps = conn.prepareStatement(sql);
    ps.setString(1, score.getName());
    ps.setString(2, score.getSubject());
    // ps.setDouble(3, score.getScore());
    //  perform 
    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 {
    //  Modify the  score He got good grades in his subjects 
    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;
    //  Began to query 
    Statement st = conn.createStatement();
    ResultSet rs = st.executeQuery(sql);
    List<Score> list = new ArrayList<Score>();
    while (rs.next()) {
      //  Here you can go through rs Get all the results 
      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));
    }
    //  The end of the 
    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;
  }