Java-JDBC-ResultSet及查询记录对象(JavaBean)封装

Java-JDBC-ResultSet及查询记录对象(JavaBean)封装

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目录

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内容

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1、ResultSet

  ResultSet结果集对象，用于封装查询结果。

• boolean next()：游标向下移动一行，判断当前行是否是最后一行（末尾，是否还有数据），有则返回true;否则返回false;

• getXxx(参数）：获取数据

  • Xxx：代码数据类型
  • 参数：
    • int ：代表列的编号，从1开始
    • String：代码列的名称

• 使用步骤

  1. 游标向下移动一行
  2. 判断是否有数据
  3. 获取数据

• 示例：遍历表account并打印

• 代码1-1：

    package cn.gaogzhen.jdbc;
  
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
  
    public class JDBCDemo4 {
    	public static void main(String[] args) {
    		Connection conn = null;
    		Statement statement = null;
    		ResultSet ret = null;
    		 // 2. 注册驱动
    		try {
    			Class.forName("com.mysql.cj.jdbc.Driver");
    			// 3. 获取连接对象Connection
    		   conn = DriverManager.getConnection("jdbc:mysql://127.0.0.1:3306/db2?serverTimezone=Asia/Shanghai", "root", "root");
    			// 4. sql语句
    			String sql = "select * from account";
    			// 5. 获取执行sql语句的对象statement
    			statement = conn.createStatement();
    			// 6. 执行sql操作,获取结果
    			ret = statement.executeQuery(sql);
    			// 7. 解析结果
    			System.out.println("ID\t姓名\t余额");
    		   while(ret.next()) {
    			   int id = ret.getInt("id");
    			   String name = ret.getString("name");
    			   double balance = ret.getDouble("balance");
    			   System.out.println(id + "\t" + name + "\t" + balance);
    		   }
    		} catch (ClassNotFoundException e) {
    			e.printStackTrace();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		} finally {
    			 // 8. 释放资源
    			if (ret != null) {
    				try {
    					ret.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
  
    			if (statement != null) {
    				try {
    					statement.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
  
    			if(conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
    		}
    	 }
    }
  

测试结果：

	ID	姓名	余额
	1	张三	500.0
	2	李四	1000.0

2、JavaBean

  JavaBean 为Java的标准类，即属性为私有，并且提供相应的get和set方法的类。

3、表 -> 对象集合

• 表名：对应类名
• 一条记录：对应一个类对象
• 列名：对应属性名
• 列类型：对应属性类型
• 数据集：对应集合

4、查询表emp数据将其封装为对象，并装入集合返回

• 表emp图示4-1：

• JavaBean Emp类代码4-1：

    package cn.gaogzhen.domain;
  
    import java.util.Date;
  
    /**
     * 员工类
     * @author gaogzhen
     *
     */
    public class Emp {
    	private int id;
    	private String ename;
    	private int job_id;
    	private int mgr;
    	private Date joindate;
    	private double salary;
    	private double bonus;
    	private int dept_id;
  
    	public Emp(int id, String ename, int job_id, int mgr, Date joindate, double salary, double bonus, int dept_id) {
    		super();
    		this.id = id;
    		this.ename = ename;
    		this.job_id = job_id;
    		this.mgr = mgr;
    		this.joindate = joindate;
    		this.salary = salary;
    		this.bonus = bonus;
    		this.dept_id = dept_id;
    	}
    	public int getId() {
    		return id;
    	}
    	public void setId(int id) {
    		this.id = id;
    	}
    	public String getEname() {
    		return ename;
    	}
    	public void setEname(String ename) {
    		this.ename = ename;
    	}
    	public int getJob_id() {
    		return job_id;
    	}
    	public void setJob_id(int job_id) {
    		this.job_id = job_id;
    	}
    	public int getMgr() {
    		return mgr;
    	}
    	public void setMgr(int mgr) {
    		this.mgr = mgr;
    	}
    	public Date getJoindate() {
    		return joindate;
    	}
    	public void setJoindate(Date joindate) {
    		this.joindate = joindate;
    	}
    	public double getSalary() {
    		return salary;
    	}
    	public void setSalary(double salary) {
    		this.salary = salary;
    	}
    	public double getBonus() {
    		return bonus;
    	}
    	public void setBonus(double bonus) {
    		this.bonus = bonus;
    	}
    	public int getDept_id() {
    		return dept_id;
    	}
    	public void setDept_id(int dept_id) {
    		this.dept_id = dept_id;
    	}
    	@Override
    	public String toString() {
    		return "Emp [id=" + id + ", name=" + ename + ", job_id=" + job_id + ", mgr=" + mgr + ", joindate=" + joindate
    				+ ", salary=" + salary + ", bonus=" + bonus + ", dept_id=" + dept_id + "]";
    	}
    }
  

• JDBCDemo05类代码4-2:

    package cn.gaogzhen.jdbc;
  
    import java.sql.Connection;
    import java.sql.DriverManager;
    import java.sql.ResultSet;
    import java.sql.SQLException;
    import java.sql.Statement;
    import java.util.ArrayList;
    import java.util.Date;
    import java.util.List;
  
    import cn.gaogzhen.domain.Emp;
  
    public class JDBCDemo5 {
    	public static void main(String[] args) {
    		List list = new JDBCDemo5().findAll();
    		System.out.println(list);
    	 }
  
    	public List findAll() {
    		Connection conn = null;
    		Statement statement = null;
    		ResultSet ret = null;
    		List list = new ArrayList<>();
    		 // 2. 注册驱动
    		try {
    			Class.forName("com.mysql.cj.jdbc.Driver");
    			// 3. 获取连接对象Connection
    		   conn = DriverManager.getConnection("jdbc:mysql:///db1?serverTimezone=Asia/Shanghai", "root", "root");
    			// 4. sql语句
    			String sql = "select * from emp";
    			// 5. 获取执行sql语句的对象statement
    			statement = conn.createStatement();
    			// 6. 执行sql操作,获取结果
    			ret = statement.executeQuery(sql);
    			// 7. 解析结果
  
    			while(ret.next()) {
    			   int id = ret.getInt("id");
    			   String ename = ret.getString("ename");
    			   int job_id = ret.getInt("job_id");
    			   int mgr = ret.getInt("mgr");
    			   Date joindate = ret.getDate("joindate");
    			   double salary = ret.getDouble("salary");
    			   double bonus = ret.getDouble("bonus");
    			   int dept_id = ret.getInt("dept_id");
    			   list.add(new Emp(id, ename, job_id, mgr, joindate, salary, bonus, dept_id));
    		   }
    		} catch (ClassNotFoundException e) {
    			e.printStackTrace();
    		} catch (SQLException e) {
    			e.printStackTrace();
    		} finally {
    			 // 8. 释放资源
    			if (ret != null) {
    				try {
    					ret.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
  
    			if (statement != null) {
    				try {
    					statement.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
  
    			if(conn != null) {
    				try {
    					conn.close();
    				} catch (SQLException e) {
    					e.printStackTrace();
    				}
    			}
    		}
    		return list;
    	}
    }
  

• 测试结果：

    [Emp [id=1001, name=孙悟空, job_id=4, mgr=1004, joindate=2000-12-17, salary=8000.0, bonus=0.0, dept_id=20], Emp [id=1002, name=卢俊义, job_id=3, mgr=1006, joindate=2001-02-20, salary=16000.0, bonus=3000.0, dept_id=30], Emp [id=1003, name=林冲, job_id=3, mgr=1006, joindate=2001-02-22, salary=12500.0, bonus=5000.0, dept_id=30], Emp [id=1004, name=唐僧, job_id=2, mgr=1009, joindate=2001-04-02, salary=29750.0, bonus=0.0, dept_id=20], Emp [id=1005, name=李逵, job_id=4, mgr=1006, joindate=2001-09-28, salary=12500.0, bonus=14000.0, dept_id=30], Emp [id=1006, name=宋江, job_id=2, mgr=1009, joindate=2001-05-01, salary=28500.0, bonus=0.0, dept_id=30], Emp [id=1007, name=刘备, job_id=2, mgr=1009, joindate=2001-09-01, salary=24500.0, bonus=0.0, dept_id=10], Emp [id=1008, name=猪八戒, job_id=4, mgr=1004, joindate=2007-04-19, salary=30000.0, bonus=0.0, dept_id=20], Emp [id=1009, name=罗贯中, job_id=1, mgr=0, joindate=2001-11-17, salary=50000.0, bonus=0.0, dept_id=10], Emp [id=1010, name=吴用, job_id=3, mgr=1006, joindate=2001-09-08, salary=15000.0, bonus=0.0, dept_id=30], Emp [id=1011, name=沙僧, job_id=4, mgr=1004, joindate=2007-05-23, salary=11000.0, bonus=0.0, dept_id=20], Emp [id=1012, name=李逵, job_id=4, mgr=1006, joindate=2001-12-03, salary=9500.0, bonus=0.0, dept_id=30], Emp [id=1013, name=小白龙, job_id=4, mgr=1004, joindate=2001-12-03, salary=30000.0, bonus=0.0, dept_id=20], Emp [id=1014, name=关羽, job_id=4, mgr=1007, joindate=2002-01-23, salary=13000.0, bonus=0.0, dept_id=10]]
  

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