Java泛型与数据库的应用

秒速五厘米 2021-09-20 09:38 270阅读 0赞

**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

![20190623073703639.png][]

**四 怎样在IDEA中导入jar包**

[https://blog.csdn.net/qq\_38000422/article/details/79962314][https_blog.csdn.net_qq_38000422_article_details_79962314]

**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<>();
    	}
    
    }

[20190623073703639.png]: /images/20210724/3c79f5a705ad414185654fd9b1e12793.png
[https_blog.csdn.net_qq_38000422_article_details_79962314]: https://blog.csdn.net/qq_38000422/article/details/79962314