Java学习-JDBC(三)

JDBC扩展

实体类和ORM

在使用JDBC操作数据库时，会发现数据是零散的，明明在数据库中是一行完整的数据，到了Java中变成一个个变量，不利于维护和管理，Java是面向对象的，一个表对应一个类，一行数据就对应Java中的一个对象，每个列对应对象的属性，所以要将数据以实体类的方式存储
ORM(Object Relational Mapping)对象到关系数据库的映射，把面向对象的概念跟数据库中表的概念对应起来，以面向对象的角度操作数据库数据，即一张表对应一个类，一行数据对应一个对象，一个列对应一个属性

//javabean类
package com.lotus.advance.pojo;
public class Employee {private Integer empId;private String empName;private Double empSalary;private Integer empAge;public Employee(Integer empId, String empName, Double empSalary, Integer empAge) {this.empId = empId;this.empName = empName;this.empSalary = empSalary;this.empAge = empAge;}public Employee() {}public Integer getEmpId() {return empId;}public void setEmpId(Integer empId) {this.empId = empId;}public String getEmpName() {return empName;}public void setEmpName(String empName) {this.empName = empName;}public Double getEmpSalary() {return empSalary;}public void setEmpSalary(Double empSalary) {this.empSalary = empSalary;}public Integer getEmpAge() {return empAge;}public void setEmpAge(Integer empAge) {this.empAge = empAge;}@Overridepublic String toString() {return "Employee{" +"empId=" + empId +", empName='" + empName + '\'' +", empSalary=" + empSalary +", empAge=" + empAge +'}';}
}
//单元测试类，用于测试ORM
package com.lotus.advance;import com.lotus.advance.pojo.Employee;
import org.junit.After;
import org.junit.Before;
import org.junit.Test;import java.sql.*;
import java.util.ArrayList;
import java.util.List;public class JDBCAdvanced {private Connection conn;private PreparedStatement statement;private ResultSet rs;//测试前与数据库建立连接@Beforepublic void init() throws SQLException {String url = "jdbc:mysql://192.168.29.201:3306/jdbc";String username = "root";String password = "123456";conn = DriverManager.getConnection(url, username, password);}/*** 获取单行多列数据* @throws SQLException*/@Testpublic void testORM() throws SQLException {String statement_sql = "select * from jdbc.t_emp where emp_id=?";statement = conn.prepareStatement(statement_sql);statement.setInt(1,2);rs = statement.executeQuery();//处理结果,如确认只有一行数据，需要做一次rs.next()的判断，才能拿到列的结果Employee employee = null;while (rs.next()) {employee = new Employee();int emp_id = rs.getInt("emp_id");String emp_name = rs.getString("emp_name");double emp_salary = rs.getDouble("emp_salary");int emp_age = rs.getInt("emp_age");employee.setEmpAge(emp_age);employee.setEmpName(emp_name);employee.setEmpId(emp_id);employee.setEmpSalary(emp_salary);System.out.println(employee);}}/*** ORM封装多个对象* @throws SQLException*/@Testpublic void testORMList() throws SQLException {String statement_sql = "select * from jdbc.t_emp where emp_age>?";statement = conn.prepareStatement(statement_sql);statement.setInt(1,20);rs = statement.executeQuery();//处理结果,如确认只有一行数据，需要做一次rs.next()的判断，才能拿到列的结果List<Employee> list = new ArrayList<>();Employee employee = null;while (rs.next()) {employee = new Employee();int emp_id = rs.getInt("emp_id");String emp_name = rs.getString("emp_name");double emp_salary = rs.getDouble("emp_salary");int emp_age = rs.getInt("emp_age");employee.setEmpAge(emp_age);employee.setEmpName(emp_name);employee.setEmpId(emp_id);employee.setEmpSalary(emp_salary);list.add(employee);   //将找到的数据存入集合中}for (Employee emp : list) {System.out.println(emp);}}//测试后关闭与数据库的连接，防止内存泄漏@Afterpublic void destory() throws SQLException {//6.释放资源if (rs != null) {rs.close();}if (statement != null) {statement.close();}if (conn != null) {conn.close();}}
}

主键回显

在数据库中，执行新增操作时，主键设置为自动增长，可以在表中直观的看到，但是在Java程序中，执行完新增后，只能得到受影响行数，无法得知当前新增数据的主键值，在Java程序中获取数据中插入新数据后的主键值，并赋值给Java对象，此操作为主键回显。

//连接和释放见上面代码的init和destory@Testpublic void testReturnPK() throws SQLException {//预编译SQL语句String sql = "insert into t_emp(emp_name,emp_salary,emp_age) values (?,?,?)";//Statement.RETURN_GENERATED_KEYS--返回新增数据主键列的值PreparedStatement preparedStatement = conn.prepareStatement(sql,Statement.RETURN_GENERATED_KEYS);Employee jack = new Employee(null, "jack", 123.45, 34);preparedStatement.setString(1,jack.getEmpName());preparedStatement.setDouble(2,jack.getEmpSalary());preparedStatement.setInt(3,jack.getEmpAge());//执行SQL，获取返回结果int result = preparedStatement.executeUpdate();if (result > 0) {System.out.println("Success");//获取当前新增数据的主键列，回显到Java中Employee对象的empId属性上//返回主键值为单行单列结果，存放在ResultSet中ResultSet keys = null;try {keys = preparedStatement.getGeneratedKeys();if (keys.next()) {int empId = keys.getInt(1);jack.setEmpId(empId);}System.out.println(jack);} finally {if (keys != null) {keys.close();}}} else{System.out.println("Failure");}}

批量操作

插入多条数据时，一条一条发送数据库执行，效率低下
通过批量操作，可提升操作效率

public void testMoreInsert() throws SQLException {///*** 1.rewriteBatchedStatements允许批量操作* 2.sql语句中使用values,最后不能加;* 3.调用addBatch(),将SQL语句进行批量添加操作* 4.统一执行批量操作，调用executeBatch()*/String url = "jdbc:mysql://192.168.29.201:3306/jdbc?rewriteBatchedStatements=true";String username = "root";String password = "Lotus!1120";conn = DriverManager.getConnection(url, username, password);//编写SQL语句String sql = "insert into t_emp(emp_name,emp_salary,emp_age) values (?,?,?)";PreparedStatement preparedStatement = conn.prepareStatement(sql);//获取当前代码执行开始时间long start = System.currentTimeMillis();for (int i = 0; i < 10000; i++) {//为占位符赋值preparedStatement.setString(1,"marry" + i);preparedStatement.setDouble(2,100.0 + i);preparedStatement.setInt(3,20 + i);//preparedStatement.executeUpdate();preparedStatement.addBatch();}preparedStatement.executeBatch();long end = System.currentTimeMillis();System.out.println("Time：" + (end - start));}