Java知识点总结(JDBC-连接步骤及CRUD)

发布时间:2019-11-19 发布网站:脚本宝典
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Java知识点总结(JDBC-连接步骤及CRUD)

@(Java知识点总结)[Java, JDBC]

连接数据库步骤

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依序关闭使用的对象连接:

  • ResultSet -> Statement -> Connection

CRUD操作

import java.sql.Connection; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException;     public class StudentDao {     private static Connection getConn() {       String driver = "com.mysql.jdbc.Driver";       String url = "jdbc:mysql://localhost:3306/test";       String username = "root";       String password = "123";       Connection conn = null;       try {           Class.forName(driver); //classLoader,加载对应驱动           //建立连接(连接对象内部包含了Socket对象,是一个远程连接。比较耗时!这是Connection对象管理的一个要点!)           //真正开发中,为了提高效率,都会使用连接池来管理连接对象!           conn = (Connection) DriverManager.getConnection(url, username, password);       } catch (ClassNotFoundException e) {           e.printStackTrace();       } catch (SQLException e) {           e.printStackTrace();       }       return conn;   }      private static int insert(User user) {       Connection conn = getConn();       int i = 0;       String sql = "insert into users (Name,Sex,Age) values(?,?,?)";       PreparedStatement pstmt = null;       try {           pstmt = (PreparedStatement) conn.prepareStatement(sql);           pstmt.setString(1, user.getName());           pstmt.setString(2, user.getSex());           pstmt.setInt(3, user.getAge());           i = pstmt.executeUpdate();           pstmt.close();           conn.close();       } catch (SQLException e) {           e.printStackTrace();       }finally {      try {       pstmt.close();      } catch (SQLException e) {       e.printStackTrace();      }      try {       conn.close();      } catch (SQLException e) {       e.printStackTrace();      }    }       return i;   }      private static int update(User user) {       Connection conn = getConn();       int i = 0;       String sql = "update users set Age='" + user.getAge() + "' where Name='" + user.getName() + "'";       PreparedStatement pstmt = null;       try {           pstmt = (PreparedStatement) conn.prepareStatement(sql);           i = pstmt.executeUpdate();           System.out.println("resutl: " + i);           pstmt.close();           conn.close();       } catch (SQLException e) {           e.printStackTrace();       }finally {      try {       pstmt.close();      } catch (SQLException e) {       e.printStackTrace();      }      try {       conn.close();      } catch (SQLException e) {       e.printStackTrace();      }    }       return i;   }      private static Integer getAll() {       Connection conn = getConn();       String sql = "select * from users";       PreparedStatement pstmt =null;       ResultSet  rs = null;       try {           pstmt = (PreparedStatement)conn.prepareStatement(sql);           rs = pstmt.executeQuery();           int col = rs.getMetaData().getColumnCount();           System.out.println("============================");           while (rs.next()) {               for (int i = 1; i <= col; i++) {                   System.out.print(rs.getString(i) + "t");                   if ((i == 2) &amp;& (rs.getString(i).length() < 8)) {                       System.out.print("t");                   }                }               System.out.println("");           }               System.out.println("============================");       } catch (SQLException e) {           e.printStackTrace();       }finally {        try {       rs.close();      } catch (SQLException e1) {       e1.printStackTrace();      }      try {       pstmt.close();      } catch (SQLException e) {       e.printStackTrace();      }      try {       conn.close();      } catch (SQLException e) {       e.printStackTrace();      }    }       return null;   }      private static int delete(String name) {       Connection conn = getConn();       int i = 0;       String sql = "delete from users where Name='" + name + "'";       PreparedStatement pstmt = null;       try {           pstmt = (PreparedStatement) conn.prepareStatement(sql);           i = pstmt.executeUpdate();           System.out.println("resutl: " + i);           pstmt.close();           conn.close();       } catch (SQLException e) {           e.printStackTrace();       }finally {      try {       pstmt.close();      } catch (SQLException e) {       e.printStackTrace();      }      try {       conn.close();      } catch (SQLException e) {       e.printStackTrace();      }    }       return i;   }      public static void main(String[] args) {    getAll();        insert(new User("张柏芝", "女", 43));        getAll();        update(new User("张三", "", 38));        delete("Achilles");        getAll();   } }
public class User {     private int id;   private int age;   private String name ;   private String sex;         public User( String name, String sex,int age) {    this();    this.age = age;    this.name = name;    this.sex = sex;   }   public User() {     }   public int getAge() {    return age;   }   public int getId() {    return id;   }   public String getName() {    return name;   }   public String getSex() {    return sex;   }   public void setAge(int age) {    this.age = age;   }   public void setId(int id) {    this.id = id;   }   public void setName(String name) {    this.name = name;   }   public void setSex(String sex) {    this.sex = sex;   }    }

执行结果:

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