设计模式之 动态代理 - ThreadLocal实现事务管理
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2022-04-16 15:15:41
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动态代理:JDK动态代理只能对实现了接口的类进入代理,采用JDK动态代理必须实现InvocationHandler接口,采用Proxy 类创建相应的代理类.
下面使用Model2(MVC)使用代理事务查询用户基本信息,使用DB2数据库:
建立表: create table T_USER ( USER_ID VARCHAR(10) not null, USER_NAME VARCHAR(30) not null, PASSWORD VARCHAR(20) not null, CONTACT_TEL VARCHAR(30), EMAIL VARCHAR(30), CREATE_DATE DATE, constraint P_KEY_1 primary key (USER_ID) ); 初始化数据: insert into t_user(user_id, user_name, password) values('root', '系统管理员', 'root');
ConnectionManager :数据库连接管理类,实现对数据库连接和事务的管理.
package gd.hz.util; import java.sql.Connection; import java.sql.DriverManager; import java.sql.SQLException; public class ConnectionManager { private ConnectionManager() { } private static ThreadLocal<Connection> threadConn = new ThreadLocal<Connection>(); // 获取数据库连接 public static Connection getConnection() { Connection conn = threadConn.get(); if (conn == null) { try { Class.forName("com.ibm.db2.jcc.DB2Driver"); conn = DriverManager.getConnection( "jdbc:db2://127.0.0.1:50000/DRP", "db2admin", "619100"); } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); } threadConn.set(conn); } return conn; } // 设置事务手动提交 public static void benigTransction(Connection conn) { try { if (conn != null) { if (conn.getAutoCommit()) { conn.setAutoCommit(false); } } } catch (SQLException e) { e.printStackTrace(); } } // 提交事务 public static void endTransction(Connection conn) { try { if (conn != null) { if (!conn.getAutoCommit()) { conn.commit(); } } } catch (SQLException e) { e.printStackTrace(); } } // 设置Connection的原始状态 public static void recoverTransction(Connection conn) { try { if (conn != null) { if (conn.getAutoCommit()) { conn.setAutoCommit(false); } else { conn.setAutoCommit(true); } } } catch (SQLException e) { e.printStackTrace(); } } // 发生异常回滚事务 public static void rollback(Connection conn) { try { if (conn != null) { conn.rollback(); } } catch (SQLException e) { e.printStackTrace(); } } // 关闭连接,并将其从当前线程删除 public static void close() { Connection conn = threadConn.get(); if (conn != null) { try { conn.close(); conn = null; threadConn.remove(); } catch (SQLException e) { e.printStackTrace(); } } } }
Model:
package gd.hz.model; import java.util.Date; //用户实体类 public class User { // 用户ID private String id; // 用户名称 private String name; // 登陆密码 private String password; // 联系电话 private String contact_tel; // 电子邮件 private String email; // 用户创建日期 private Date create_date; public String getId() { return id; } public void setId(String id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getPassword() { return password; } public void setPassword(String password) { this.password = password; } public String getContact_tel() { return contact_tel == null ? "" : contact_tel; } public void setContact_tel(String contact_tel) { this.contact_tel = contact_tel; } public String getEmail() { return email == null ? "" : email; } public void setEmail(String email) { this.email = email; } public Date getCreate_date() { return create_date; } public void setCreate_date(Date create_date) { this.create_date = create_date; } }
DAO接口:
package gd.hz.dao; import gd.hz.model.User; import java.sql.SQLException; public interface UserDAO { public User selUser(String id) throws SQLException; }
DAO实现类:
package gd.hz.dao; import java.sql.Connection; import java.sql.PreparedStatement; import java.sql.ResultSet; import java.sql.SQLException; import gd.hz.model.User; import gd.hz.util.ConnectionManager; public class UserDAOImpl implements UserDAO { // 根据ID查询用户 public User selUser(String id) throws SQLException { ResultSet resu = null; String sql = "SELECT * FROM DB2ADMIN.T_USER WHERE USER_ID = ?"; Connection conn = ConnectionManager.getConnection(); PreparedStatement pstat = conn.prepareStatement(sql); User user = null; try { pstat.setString(1, id); resu = pstat.executeQuery(); if (resu.next()) { user = getUser(resu); } } finally { if (resu != null) { resu.close(); } if (pstat != null) { pstat.close(); } } return user; } // 获取用户 private User getUser(ResultSet resu) throws SQLException { User user = new User(); user.setId(resu.getString("USER_ID")); user.setName(resu.getString("USER_NAME")); user.setPassword(resu.getString("PASSWORD")); user.setContact_tel(resu.getString("CONTACT_TEL")); user.setEmail(resu.getString("EMAIL")); user.setCreate_date(resu.getTimestamp("CREATE_DATE")); return user; } }
Manager接口:
package gd.hz.manager; import gd.hz.model.User; public interface UserManager { public User findUser(String id) throws Exception; }
Manager实现类:
package gd.hz.manager; import java.sql.SQLException; import gd.hz.dao.UserDAO; import gd.hz.dao.UserDAOImpl; import gd.hz.model.User; public class UserManagerImpl implements UserManager { private UserDAO userDAO = null; public UserManagerImpl() { userDAO = new UserDAOImpl(); } public User findUser(String id) throws SQLException { return userDAO.selUser(id); } }
创建代理类:
package gd.hz.util; import java.lang.reflect.InvocationHandler; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; import java.lang.reflect.Proxy; import java.sql.Connection; //Manager代理类 public class TransctionProxy implements InvocationHandler { private Object obj = null; // obj:需要代理的类 public Object newProxyInstance(Object obj) { this.obj = obj; return Proxy.newProxyInstance(this.obj.getClass().getClassLoader(), this.obj.getClass().getInterfaces(), this); } @Override public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { // 用于接收参数 Object param = null; // 如果是以下方法开头,则代理事务 if (method.getName().startsWith("add") || method.getName().startsWith("modify") || method.getName().startsWith("find") || method.getName().startsWith("del")) { Connection conn = ConnectionManager.getConnection(); try { // 手动提交事务 ConnectionManager.benigTransction(conn); param = method.invoke(obj, args); // 提交事务 ConnectionManager.endTransction(conn); } catch (Exception e) { // 回滚事务 ConnectionManager.rollback(conn); if (e instanceof InvocationTargetException) { InvocationTargetException inv = (InvocationTargetException) e; throw inv.getTargetException(); } else { throw new Exception("操作失败!"); } } finally { // 还原状态 ConnectionManager.recoverTransction(conn); ConnectionManager.close(); } } return param; } }
测试:
package gd.hz.util; import gd.hz.manager.UserManager; import gd.hz.manager.UserManagerImpl; import gd.hz.model.User; public class Test { public static void main(String[] args) throws Exception { TransctionProxy transctionProxy = new TransctionProxy(); // //产生代理对象 UserManager userManager = (UserManager) transctionProxy .newProxyInstance(new UserManagerImpl()); User user = userManager.findUser("root"); System.out.println("用户名:" + user.getName()); } }
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