JTA 使用 MySQL 分布式事务

假定在MySQL实例1上有表

create table person(
    id int, 
    name varchar(32)
)

MySQL实例2上也有一张同样的表，现在从实例1中的 person 表中删除一条数据，并把这条数据插入到实例2的表中，这两个操作在同一个事务中，因为跨越了数据库实例，涉及到了分布式事务。

MySQL实现了分布式事务，查看数据库是否启用了 XA 事务：

show variables like 'innodb_support_xa';

MySQL 关于xa的命令：

xa start 'a';
sql 语句;
xa end 'a';
xa prepare 'a';
xa commit 'a';

与正常事务相比，XA 命令多了 prepare，询问是否准备好，事务管理器根据 prepare 返回的结果进行操作。

以上命令是分布式事务的操作方法，在一个命令行中输入上述命令，并不是真实的分布式事务。可以使用 JTA 来控制MySQL的 XA：

public class JTA_MySQL {

    public static void main(String[] args) {
        XADataSource xaDs1 = JTA_MySQL.getDataSource(
                "jdbc:mysql://172.30.60.126:3306/db_zhang", "root",
                "root");
        XAConnection xaCon1 = null;
        XAResource xaRes1 = null;
        Connection conn1 = null;
        Statement stmt1 = null;

        XADataSource xaDs2 = JTA_MySQL.getDataSource(
                "jdbc:mysql://172.30.60.124:3306/db_zhang", "root",
                "root");
        XAConnection xaCon2 = null;
        XAResource xaRes2 = null;
        Connection conn2 = null;
        Statement stmt2 = null;

        int ret1 = 0;
        int ret2 = 0;

        Xid xid1 = new MyXid(100, new byte[] { 0x01 }, new byte[] { 0x02 });
        Xid xid2 = new MyXid(100, new byte[] { 0x01 }, new byte[] { 0x03 });
        try {
            xaCon1 = getXAConnetion(xaDs1);
            conn1 = getConnection(xaCon1);
            stmt1 = conn1.createStatement();
            xaRes1 = xaCon1.getXAResource();

            xaCon2 = getXAConnetion(xaDs2);
            conn2 = getConnection(xaCon2);
            stmt2 = conn2.createStatement();
            xaRes2 = xaCon2.getXAResource();

            xaRes1.start(xid1, XAResource.TMNOFLAGS);
            stmt1.execute("delete from person where id=1");
            xaRes1.end(xid1, XAResource.TMSUCCESS);
            
            xaRes2.start(xid2, XAResource.TMNOFLAGS);
            stmt2.execute("insert into person select 1, 'zhang'");
            xaRes2.end(xid2, XAResource.TMSUCCESS);
            
            ret1 = xaRes1.prepare(xid1);
            ret2 = xaRes2.prepare(xid2);
        
            if (XAResource.XA_OK == ret1 && XAResource.XA_OK == ret2) {
                xaRes1.commit(xid1, false);
                xaRes2.commit(xid2, false);
                System.out.println("提交分布式事务");
            } else {
                xaRes1.rollback(xid1);
                xaRes2.rollback(xid2);
                System.out.println("回退分布式事务");
            }
        } catch (SQLException e) {
            e.printStackTrace();
        } catch (XAException e) {
            e.printStackTrace();
        }
    }

    private static XADataSource getDataSource(String url, String user,
            String password) {
        MysqlXADataSource dataSource = new MysqlXADataSource();
        dataSource.setUrl(url);
        dataSource.setUser(user);
        dataSource.setPassword(password);
        return dataSource;
    }

    public static XAConnection getXAConnetion(XADataSource dataSource) {
        XAConnection XAConn = null;
        try {
            XAConn = dataSource.getXAConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return XAConn;
    }

    public static Connection getConnection(XAConnection XAConn) {
        Connection conn = null;
        try {
            conn = XAConn.getConnection();
        } catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }

    public static void closeConnection(Connection conn) {
        try {
            conn.close();
        } catch (SQLException e) {
            System.out.println("连接关闭失败");
        }
    }
}

 MyXid 类：

public class MyXid implements Xid {
    private int formatId;
    private byte[] globalTid;
    private byte[] branchQ;
    
    public MyXid(int formatId, byte[] globalTid, byte[] branchQ) {
        this.formatId = formatId;
        this.globalTid = globalTid;
        this.branchQ = branchQ;
    }
    
    public byte[] getBranchQualifier() {
        return this.branchQ;
    }

    public int getFormatId() {
        return formatId;
    }

    public byte[] getGlobalTransactionId() {
        return this.globalTid;
    }
}