设计模式之 动态代理 - ThreadLocal实现事务管理
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:
Sql代码 
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.
Java代码 
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:
Java代码
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:
Java代码
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:
Java代码
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:
Java代码
package gd.hz.manager;
import gd.hz.model.User;
public interface UserManager {
public User findUser(String id) throws Exception;
}
Manager实现类:
Java代码
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:
Java代码
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:
Java代码
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());
}
}