反射机制什么是反射？
class类概述
一个类的组成部分：
Class:表示类
属性：Field
方法：Method
构造方法：Constructor
Class类的常用方法
String getName():获取类名称，包含包名；
newInstance():创建类的实例
forName(String className):根据类名返回类的对象
三种返回类对象的方式
package com.m.demo;
import static org.junit.jupiter.api.Assertions.*;
import org.junit.jupiter.api.Test;
import com.m.domain.Users;
class test01 {
@Test
void test() throws ClassNotFoundException {
// 方式1：通过类名.class 但是有硬编码
Class uClass=Users.class;
System.out.println(uClass);
// 方式2：通过实例化对象.getclass()
Users u=new Users();
Class uclass1 = u.getClass();
System.out.println(uclass1);
// 方式3：通过class.forName("类的全路径");
Class uclass2=Class.forName("com.m.domain.Users");
System.out.println(uclass2);
}
}
获取Constructor对象
Constructor类常用方法
//使用构造器构建实例化对象 // 无参构造 Constructor con=uclass2.getConstructor(); Object o=con.newInstance(); System.out.println(o); // 有参构造 Constructor con1=uclass2.getConstructor(int.class,String.class,String.class); Object o1=con1.newInstance(1,"abc","123"); System.out.println(o1);
获得Field的方法
需要通过class类实例化对象！
package com.m.demo;
import java.lang.reflect.Field;
public class test {
public static void main(String[] args) throws Exception {
Class uclass2=Class.forName("com.m.domain.Users");
System.out.println(uclass2);
// 获取私有属性
Field field = uclass2.getDeclaredField("id");
System.out.println(field);
field.setAccessible(true);
Object object = uclass2.newInstance();//需要实例化对象！！！
field.set(object, 5);
System.out.println(field.get(object));
}
}
Method类常用方法
getMethod(“方法名称”,方法参数的class类型)
执行方法
package com.m.demo;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class test {
public static void main(String[] args) throws Exception {
Class uclass2=Class.forName("com.m.domain.Users");
System.out.println(uclass2);
Object object = uclass2.newInstance();//需要实例化对象！！！
// 获取公有方法
Method m=uclass2.getMethod("printf");
m.invoke(object);
// 获取私有方法
Method m2= uclass2.getDeclaredMethod("print");
m2.setAccessible(true);
m2.invoke(object);
}
}
数据库连接池
原理图示：
C3P0连接池
root 000000 jdbc:mysql://localhost:3306/emp com.mysql.jdbc.Driver 30000 30 5 30 100 2 200
使用eclipse如果只导一个包是不够的，会报Exception in thread “main” java.lang.NoClassDefFoundError: com/mchange/v2/ser/Indirector。
需要导入mchange包。
一共需要三个包
C3p0Utils.java文件
package com.m.Utils;
import java.io.IOException;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import com.mchange.v2.c3p0.ComboPooledDataSource;
public class C3P0Utils {
//创建连接池对象
private static ComboPooledDataSource dataSource = new ComboPooledDataSource();
//连接
public static Connection getConnection() throws Exception, IOException {
return dataSource.getConnection();
}
//放入连接池
public static void closeAll(ResultSet rs,Statement st,Connection con) {
try {
if(rs!=null) {
rs.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(st!=null) {
st.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(con!=null) {
con.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void closeAll(Statement st,Connection con) {
try {
if(st!=null) {
st.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
try {
if(con!=null) {
con.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
public static void closeAll(Connection con) {
try {
if(con!=null) {
con.close();
}
} catch (SQLException e) {
e.printStackTrace();
}
}
}
测试类
package com.m.demo;
import java.io.IOException;
import java.sql.Connection;
import com.m.Utils.C3P0Utils;
public class test2 {
public static void main(String[] args) throws Exception {
Connection c = C3P0Utils.getConnection();
if(c!=null) {
System.out.println("连接成功");
}
}
}
DBUtils框架使用DBUtils对应的实体类必须提供无参构造
jar包官网下载
package com.m.Utils;
import javax.sql.DataSource;
import com.mchange.v2.c3p0.ComboPooledDataSource;
public class C3P0Utils2 {
private static ComboPooledDataSource dataSource = new ComboPooledDataSource();
public static DataSource getDataSource() {
return dataSource;
}
}
创建数据库实体类->DAO(接口实现类)实现CRUD操作->service (接口实现类)处理事件->测试类（三层结构）
创建数据库实体类
package com.m.domain;
public class Users {
private int id;
private String username;
private String password;
public Users(){
}
public Users(int id, String username, String password) {
super();
this.id = id;
this.username = username;
this.password = password;
}
public Users(String username, String password) {
super();
this.username = username;
this.password = password;
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getUsername() {
return username;
}
public void setUsername(String username) {
this.username = username;
}
public String getPassword() {
return password;
}
public void setPassword(String password) {
this.password = password;
}
public void printf() {
System.out.println(username+" "+password);
}
private void print() {
System.out.println(username);
}
@Override
public String toString() {
return "Users [id=" + id + ", username=" + username + ", password=" + password + "]";
}
}
DAO(接口实现类)实现CRUD操作
package com.m.DAO;
import java.util.List;
import com.m.domain.Users;
public interface usersDAO {
// 插入数据
public Integer insertUsers(Users u) throws Exception;
// 修改密码数据
public Integer updateUserById(int i,String s) throws Exception;
// 删除数据
public Integer deleteUserById(int i) throws Exception;
// 查询所有数据
public List selectUsers() throws Exception;
}
package com.m.DAO;
import java.sql.Connection;
import java.util.List;
import org.apache.commons.dbutils.QueryRunner;
import org.apache.commons.dbutils.handlers.BeanListHandler;
import com.m.Utils.C3P0Utils2;
import com.m.domain.Users;
public class usersDAOImpl implements usersDAO {
//不需要再创建连接！使用queryRunner实现增删改查 需要datasource
QueryRunner qr=new QueryRunner(C3P0Utils2.getDataSource());
@Override
public Integer insertUsers(Users u) throws Exception {
String sql="insert into users values(null,?,?)";
// 创建数组装元素
Object parments[]=new Object[] {u.getUsername(),u.getPassword()};
int i = qr.update(sql, parments);
return i;
}
@Override
public Integer updateUserById(int i,String s) throws Exception {
String sql="update users set password=? where id=?";
// 创建数组装元素
Object parments[]=new Object[] {s,i};
int j = qr.update(sql, parments);
return j;
}
@Override
public Integer deleteUserById(int i) throws Exception {
String sql="delete from users where id=?";
// 创建数组装元素
Object parments[]=new Object[] {i};
int j = qr.update(sql, parments);
return j;
}
@Override
public List selectUsers() throws Exception {
String sql="select * from users";
// BeanListHandler将数据库中的内容封装成一个List 要求：数据库列名和实例化类 属性名完全一致
List list = qr.query(sql, new BeanListHandler(Users.class));
return list;
}
}
service (接口实现类)处理事件
package com.m.service;
import java.util.List;
import com.m.domain.Users;
public interface usersService {
// 插入数据
public Integer insertUsers(Users u) throws Exception;
// 修改密码数据
public Integer updateUserById(int i,String s) throws Exception;
// 删除数据
public Integer deleteUserById(int i) throws Exception;
// 查询所有数据
public List selectUsers() throws Exception;
}
package com.m.service;
import java.util.List;
import com.m.DAO.usersDAO;
import com.m.DAO.usersDAOImpl;
import com.m.domain.Users;
public class usersServiceImpl implements usersService {
usersDAO ud=new usersDAOImpl();
@Override
public Integer insertUsers(Users u) throws Exception {
return ud.insertUsers(u);
}
@Override
public Integer updateUserById(int i,String s) throws Exception {
return ud.updateUserById(i, s);
}
@Override
public Integer deleteUserById(int i) throws Exception {
return ud.deleteUserById(i);
}
@Override
public List selectUsers() throws Exception {
return ud.selectUsers();
}
}
测试类
package com.m.demo;
import java.util.List;
import com.m.domain.Users;
import com.m.service.usersService;
import com.m.service.usersServiceImpl;
public class test3 {
public static void main(String[] args) throws Exception {
usersService us=new usersServiceImpl();
// Integer i = us.insertUsers(new Users("赵六","123"));
// if(i>0) {
// System.out.println("插入成功");
// }else {
// System.out.println("插入失败");
// }
// us.updateUserById(5, "456");
// if(us.deleteUserById(6)>0) {
// System.out.println("修改成功");
// }else {
// System.out.println("修改失败");
// }
List list = us.selectUsers();
list.stream().forEach(a->System.out.println(a));
}
}
