Java泛型与数据库应用实例详解

2021-04-03 我要评论

本文实例讲述了Java泛型与数据库应用。分享给大家供大家参考，具体如下：

一点睛

BaseDao定义了基本的数据库增删查改，之后可以继承该泛型类，实现各自的增删查改，或者使用超类的增删查改，同时每个继承类还能增加自己的操作。

二实战

1 BaseDao.java

import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
public class BaseDao<T> {
  Connection connection;
  PreparedStatement pStatement;
  String urlString = "jdbc:mysql://localhost:3306/student?useUnicode=true&characterEncoding=UTF8";
  String drivString = "com.mysql.jdbc.Driver";
  void OpenDB() {
    try {
      if (connection == null) {
        Class.forName(drivString);
        this.connection = DriverManager.getConnection(urlString, "root", "123456");
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  void CloseDB() {
    try {
      if (pStatement != null) pStatement.close();
      if (connection != null) connection.close();
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
  public void Save( T t ) {
    OpenDB();
    String table = "";
    String sqlString = "insert into ";
    try {
      table = t.getClass().getSimpleName();
      Field[] fields = t.getClass().getDeclaredFields();
      sqlString += table;
      String sqlNameString = "";
      String sqlValString = "";
      for (Field field : fields) {
        sqlNameString += field.getName() + ",";
        sqlValString += "?,";
      }
      sqlNameString = sqlNameString.substring(0, sqlNameString.length() - 1);
      sqlValString = sqlValString.substring(0, sqlValString.length() - 1);
      pStatement = connection.prepareStatement(sqlString + " (" + sqlNameString + ") values (" + sqlValString + ")");
      int n = 1;
      for (Field field : fields) {
        field.setAccessible(true);
        System.out.println(field.get(t).toString());
        pStatement.setString(n, field.get(t).toString());
        n++;
      }
      pStatement.executeUpdate();
      CloseDB();
    } catch (Exception e) {
      e.printStackTrace();
      CloseDB();
    }
  }
  public void Del( T t ) {
  }
  public void Update( T t ) {
  }
  public void Search( T t ) {
  }
}

2 StudentDao.java

public class StudentDao extends BaseDao<Student> {
}

3 TeacherDao.java

public class TeacherDao extends BaseDao<Teacher> {
}

4 Student.java

public class Student {
  public String name;
  public int age;
  public String dept;
  /**
  * @return the name
  */
  public String getName() {
   return name;
  }
  /**
  * @param name the name to set
  */
  public void setName(String name) {
   this.name = name;
  }
  /**
  * @return the age
  */
  public int getAge() {
   return age;
  }
  /**
  * @param age the age to set
  */
  public void setAge(int age) {
   this.age = age;
  }
  /**
  * @return the dept
  */
  public String getDept() {
   return dept;
  }
  /**
  * @param dept the dept to set
  */
  public void setDept(String dept) {
   this.dept = dept;
  }
}

5 Teacher.java

public class Teacher {
}

6 TestDao.java

public class TestDao {
  public static void main(String[] args) {
   System.out.println("ok");
   Student stud=new Student();
   stud.age=20;
   stud.name="zhangsan";
   stud.dept="computer";
   StudentDao sd=new StudentDao();
   sd.Save(stud);
   System.out.println(stud.dept);
  }
}

三运行

ok
zhangsan
20
computer
computer

四怎样在IDEA中导入jar包

可参考附录：IDEA连接数据库（导入jar包）

五另外一种写法

StudentDao.java

public class StudentDao<M> extends BaseDao<M> {    // 这里的M可以是任意合法标识符
}

TestDao.java

public class TestDao {
 public static void main(String[] args) {
 System.out.println("ok");
 Student stud=new Student();
 stud.age=20;
 stud.name="zhangsan2";
 stud.dept="computer";
 StudentDao<Student> sd=new StudentDao<>();  // 这里要说明是Student
 sd.Save(stud);
 System.out.println(stud.dept);
 TeacherDao<Teacher> te= new TeacherDao<>();
 }
}

附：IDEA连接数据库（导入jar包）

Java连接 MySQL 需要驱动包，最新版下载地址为：http://dev.mysql.com/downloads/connector/j/，解压后得到jar库文件，然后在对应的项目中导入该库文件。

IDEA导入jar过程:新建文件夹（名称任意，这里使用Lib）,导入mysql-connector-java-*.*.**-bin.jar如下图