动手写web框架(9): 事务实现

定义事务注解

@Transaction注解只能用于方法级别。

Transaction

package org.smart4j.framework.annotation;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

/**
 * 定义需要事务控制的方法
 * Created by Roger on 2016/11/30.
 */
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Transaction {
}

事务操作工具

每个线程维护本地变量Connection，提供开启事务、提交事务、回滚事务等操作。

DBUtil

package org.smart4j.framework.util;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.smart4j.framework.helper.ConfigHelper;

import java.sql.Connection;
import java.sql.DriverManager;

/**
 * Created by Roger on 2016/11/30.
 */
public final class DBUtil {
    private static final Logger LOGGER = LoggerFactory.getLogger(DBUtil.class);

    // 用于放置数据库连接的局部线程变量
    private static ThreadLocal<Connection> connContainer = new ThreadLocal<>();

    /**
     * 获取数据库连接
     *
     * @return
     */
    public static Connection getConnection() {
        Connection conn = connContainer.get();
        if (conn == null) {
            try {
                Class.forName(ConfigHelper.getJdbcDriver());
                conn = DriverManager.getConnection(ConfigHelper.getJdbcUrl(), ConfigHelper.getJdbcUsername(), ConfigHelper.getJdbcPassword());
            } catch (Exception e) {
                LOGGER.error("database get connection error", e);
                throw new RuntimeException(e);
            } finally {
                connContainer.set(conn);
            }
        }
        return conn;
    }

    /**
     * 关闭数据库连接
     */
    public static void closeConnection() {
        Connection conn = connContainer.get();
        if (conn != null) {
            try {
                conn.close();
            } catch (Exception e) {
                LOGGER.error("database close connection error", e);
                throw new RuntimeException(e);
            } finally {
                connContainer.remove();
            }
        }
    }

    /**
     * 开启事务
     */
    public static void beginTransaction() {
        Connection conn = getConnection();
        if (conn != null) {
            try {
                conn.setAutoCommit(false);
            } catch (Exception e) {
                LOGGER.error("database begin transaction error", e);
                throw new RuntimeException(e);
            }
        }
    }

    /**
     * 提交事务
     */
    public static void commitTransaction() {
        Connection conn = getConnection();
        if (conn != null) {
            try {
                conn.commit();
            } catch (Exception e) {
                LOGGER.error("database commit transaction error", e);
                throw new RuntimeException(e);
            } finally {
                closeConnection();
            }
        }
    }

    /**
     * 回滚事务
     */
    public static void rollbackTransaction() {
        Connection conn = getConnection();
        if (conn != null) {
            try {
                conn.rollback();
            } catch (Exception e) {
                LOGGER.error("database rolleback transaction error", e);
                throw new RuntimeException(e);
            } finally {
                closeConnection();
            }
        }
    }
}

事务切面类

TransactionProxy类实现Proxy接口，在doProxy()方法中完成事务控制的相关逻辑。

内部定义一个FLAG_HOLDER的本地线程变量，用于保证同一线程中事务控制相关逻辑只会执行一次。

使用@Transaction注解的方法才会执行事务相关逻辑。

TransactionProxy

package org.smart4j.framework.proxy;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.smart4j.framework.annotation.Transaction;
import org.smart4j.framework.util.DBUtil;

import java.lang.reflect.Method;

/**
 * Created by Roger on 2016/11/30.
 */
public class TransactionProxy implements Proxy {

    private static final Logger LOGGER = LoggerFactory.getLogger(TransactionProxy.class);

    // 保证同一线程中事务控制相关逻辑只会执行一次
    private static final ThreadLocal<Boolean> FLAG_HOLDER = new ThreadLocal<Boolean>(){
        @Override
        protected Boolean initialValue() {
            return false;
        }
    };

    @Override
    public Object doProxy(ProxyChain proxyChain) throws Throwable {
        Object result;
        boolean flag = FLAG_HOLDER.get();
        Method method = proxyChain.getTargetMethod();
        if (!flag && method.isAnnotationPresent(Transaction.class)){
            FLAG_HOLDER.set(true);
            try {
                DBUtil.beginTransaction();
                LOGGER.debug("begin transaction");
                result = proxyChain.doProxyChain();
                DBUtil.commitTransaction();
                LOGGER.debug("commit transaction");
            } catch (Exception e) {
                DBUtil.rollbackTransaction();
                LOGGER.debug("rollback transaction");
                throw e;
            } finally {
                FLAG_HOLDER.remove();
            }
        }else {
            result = proxyChain.doProxyChain();
        }
        return result;
    }
}

框架中添加事务机制

在AopHelper类中createProxyMap()方法中添加事务代理机制addTransactionProxy()，之前AOP部分只是添加了普通的切面代理。