试题分析

一，查询所有学生记录，包含年级名称

   public class BaseDao {
          /**
     * 数据库连接字符串
     */
    private static final String DRIVER = "com.mysql.jdbc.Driver";
    private static final String URL = "jdbc:mysql://localhost:3306/myschool?useUniCode=true&characterEncoding=utf-8";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "root";

    private Connection conn;
    private PreparedStatement statement;
    private ResultSet rs;
    /**
     * 获取连接的方法
     */
    public Connection getConnection() {
        try {
            Class.forName(DRIVER);
            //判断连接对象是否为空或者当前连接对象是否是isClosed()已经关闭的
            if(conn==null||conn.isClosed()){
                conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            }
            
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;

    }

    /**
     * 增删改
     * 
     * @throws Exception
     */
    public int executeUpdate(String sql, Object... obj) throws Exception {
        // 获取连接
        getConnection();
        // 获取PreparedStatement对象
        
        statement = conn.prepareStatement(sql);
        // 循环加载参数
        for (int i = 1; i <= obj.length; i++) {
            statement.setObject(i, obj[i-1]);
        }
        // 执行SQL
        int count = statement.executeUpdate();

        return count;
    }

    /**
     * 查询
     * @throws SQLException 
     */
    public ResultSet executeQuery(String sql, Object... obj) throws Exception {
        // 获取连接
        getConnection();
        // 获取PreparedStatement对象
        statement = conn.prepareStatement(sql);
        // 循环加载参数
        for (int i = 1; i <= obj.length; i++) {
            
            statement.setObject(i, obj[i-1]);
        }
        rs = statement.executeQuery();
        return rs;
    }

    /**
     * 关闭连接
     * @throws Exception 
     */
    public void closeResource() throws Exception {
        if(rs!=null){
            rs.close();
        }
        if(statement!=null){
            statement.close();
        }
        if(conn!=null){
            //关闭连接
            conn.close();
        }
    }
}            

public interface IStudentDao {
    /**
     * 查询所有学生信息，包含年级名称
     * 一个学生对应一个年级
     * 
     */
    public List<Student> getAllStudent() throws Exception;
    
    
}

public class IStudentDaoImpl extends BaseDao implements IStudentDao{

    @Override
    public List<Student> getAllStudent() throws Exception {
        List<Student> list=new ArrayList<Student>();
        String sql="SELECT * FROM Student,Grade WHERE Student.GradeId=Grade.GradeId";
        ResultSet rs = executeQuery(sql);
        if(rs!=null){
            while(rs.next()){
                //获取学生信息
                Student student=new Student();
                student.setGradeId(rs.getInt("gradeId"));
                student.setStudentName(rs.getString("StudentName"));
                student.setStudentNo(rs.getInt("studentNo"));
                //获取的就是当前学生的年级信息
                Grade grade=new Grade();
                grade.setGradeName(rs.getString("gradeName"));
                student.setGrade(grade);
                
                
                list.add(student);
            }
        }
        closeResource();
        return list;
    }
    
    

}

public class Student {
    private int studentNo;
    private String studentName;
    private int gradeId;

    
    //只要拿到学生就能拿到对应学生的年级信息
    private Grade grade;
    
    public Grade getGrade() {
        return grade;
    }
    public void setGrade(Grade grade) {
        this.grade = grade;
    }
    public int getStudentNo() {
        return studentNo;
    }
    public void setStudentNo(int studentNo) {
        this.studentNo = studentNo;
    }
    public String getStudentName() {
        return studentName;
    }
    public void setStudentName(String studentName) {
        this.studentName = studentName;
    }
    public int getGradeId() {
        return gradeId;
    }
    public void setGradeId(int gradeId) {
        this.gradeId = gradeId;
    }
    public Student(int studentNo, String studentName, int gradeId) {
        this.studentNo = studentNo;
        this.studentName = studentName;
        this.gradeId = gradeId;
    }
    public Student() {
        
    }
    
}

public interface IStudentService {
    /**
     * 查询所有学生信息，包含年级名称
     * 
     * 
     */
    public List<Student> getAllStudent() throws Exception;
}

public class IStudentServiceImpl implements IStudentService{
    //创建Dao层对象
    IStudentDao studentDao=new IStudentDaoImpl();
    
    
    @Override
    public List<Student> getAllStudent() throws Exception {
        return studentDao.getAllStudent();
    }

}

public class MyMian {
    //创建Service对象
    static IStudentService studentService=new IStudentServiceImpl();
    static IGradeService gradeService=new IGradeServiceImpl();
    public static void main(String[] args) throws Exception {
        System.out.println("=================查询所有学生信息========================");
        List<Student> allStudent = studentService.getAllStudent();
        for (Student student : allStudent) {
            System.out.println("学生姓名："+student.getStudentName()+"	学生年级："+student.getGradeId()+"	年级名称："+student.getGrade().getGradeName());
            
        }
}

二，查询S1年级下的学生记录

public class BaseDao {
    /**
     * 数据库连接字符串
     */
    private static final String DRIVER = "com.mysql.jdbc.Driver";
    private static final String URL = "jdbc:mysql://localhost:3306/myschool?useUniCode=true&characterEncoding=utf-8";
    private static final String USERNAME = "root";
    private static final String PASSWORD = "root";

    private Connection conn;
    private PreparedStatement statement;
    private ResultSet rs;
    /**
     * 获取连接的方法
     */
    public Connection getConnection() {
        try {
            Class.forName(DRIVER);
            //判断连接对象是否为空或者当前连接对象是否是isClosed()已经关闭的
            if(conn==null||conn.isClosed()){
                conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
            }
            
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;

    }

    /**
     * 增删改
     * 
     * @throws Exception
     */
    public int executeUpdate(String sql, Object... obj) throws Exception {
        // 获取连接
        getConnection();
        // 获取PreparedStatement对象
        
        statement = conn.prepareStatement(sql);
        // 循环加载参数
        for (int i = 1; i <= obj.length; i++) {
            statement.setObject(i, obj[i-1]);
        }
        // 执行SQL
        int count = statement.executeUpdate();

        return count;
    }

    /**
     * 查询
     * @throws SQLException 
     */
    public ResultSet executeQuery(String sql, Object... obj) throws Exception {
        // 获取连接
        getConnection();
        // 获取PreparedStatement对象
        statement = conn.prepareStatement(sql);
        // 循环加载参数
        for (int i = 1; i <= obj.length; i++) {
            
            statement.setObject(i, obj[i-1]);
        }
        rs = statement.executeQuery();
        return rs;
    }

    /**
     * 关闭连接
     * @throws Exception 
     */
    public void closeResource() throws Exception {
        if(rs!=null){
            rs.close();
        }
        if(statement!=null){
            statement.close();
        }
        if(conn!=null){
            //关闭连接
            conn.close();
        }
    }
}

public interface IGradeDao {
    /**
     * 查询年级下的所有学生信息
     * 一个年级有多名学生
     */
    public Grade getStudentByGrade(String gradeName) throws Exception;
}

public class IGradeDaoImpl extends BaseDao implements IGradeDao{

    @Override
    public Grade getStudentByGrade(String gradeName) throws Exception {
        Grade grade=new Grade();
        String sql="SELECT * FROM Student,Grade WHERE Student.GradeId=Grade.GradeId AND GradeName=?";
        ResultSet rs = executeQuery(sql, gradeName);
        if(rs!=null){
            
            while (rs.next()) {
                
                //获取年级信息
                grade.setGradeName(rs.getString("gradeName"));
                //获取学生信息
                Student student=new Student();
                student.setGradeId(rs.getInt("gradeId"));
                student.setStudentName(rs.getString("StudentName"));
                student.setStudentNo(rs.getInt("studentNo"));
                //将查询出来的学生信息添加到集合当中
                grade.getStulist().add(student);
            }
            
        }
        return grade;
    }

}

public class Grade {
    private int gradeId;
    private String gradeName;
    private List<Student> stulist=new ArrayList<Student>();
    public List<Student> getStulist() {
        return stulist;
    }
    public void setStulist(List<Student> stulist) {
        this.stulist = stulist;
    }
    public int getGradeId() {
        return gradeId;
    }
    public void setGradeId(int gradeId) {
        this.gradeId = gradeId;
    }
    public String getGradeName() {
        return gradeName;
    }
    public void setGradeName(String gradeName) {
        this.gradeName = gradeName;
    }
    public Grade(int gradeId, String gradeName) {
        this.gradeId = gradeId;
        this.gradeName = gradeName;
    }
    public Grade() {
        
    }
}

public interface IGradeService {
    /**
     * 查询年级下的所有学生信息
     * 一个年级有多名学生
     */
    public Grade getStudentByGrade(String gradeName) throws Exception;
}

public class IGradeServiceImpl implements IGradeService{
    
    IGradeDao gradeDao=new IGradeDaoImpl();

    @Override
    public Grade getStudentByGrade(String gradeName) throws Exception {
        // TODO Auto-generated method stub
        return gradeDao.getStudentByGrade(gradeName);
    }

}

public class MyMian {
    //创建Service对象
    static IStudentService studentService=new IStudentServiceImpl();
    static IGradeService gradeService=new IGradeServiceImpl();
    public static void main(String[] args) throws Exception {

        Grade grade = gradeService.getStudentByGrade("S1");
        for (Student stu : grade.getStulist()) {
            System.out.println(stu.getStudentName());
        }
    }
}