使用动态代理实现用AOP对数据库进行操作

要实现对数据库的操作，离不开数据源（DataSource）或者连接（Connection）,但是通常来说对数据库的操作都应该放在DAO中，而DAO又不应该与应用服务器相关联，所以一般都使用连接（Connection）。现在我们这里就有一个问题了，怎么在拦截器中获得连接。我想可以通过两种方式获得：
在分别讨论这两种方法之前，我们需要先讨论一下在处理数据库的时候的异常的处理。我这里做了一个TransactionException继承至RuntimeException然后在拦截器里面抛出，再又应用框架处理这个异常。下面试这个类的代码：
public class TransactionException extends RuntimeException {
    private Throwable superException;
    private String myMessage;
   
    public TransactionException(Throwable throwable){
        super(throwable);
        this.superException = throwable;
    }
   
    public TransactionException(Throwable throwable,String message){
        super(message,throwable);
        this.superException = throwable;
        this.myMessage = message;
    }

    /**
     * @return Returns the myMessage.
     */
    public String getMessage() {
        return myMessage;
    }

    /**
     * @return Returns the superException.
     */
    public Throwable getSuperException() {
        return superException;
    }

    /**
     * @param myMessage The myMessage to set.
     */
    public void setMyMessage(String message) {
        this.myMessage = message;
    }

    /**
     * @param superException The superException to set.
     */
    public void setSuperException(Throwable superException) {
        this.superException = superException;
    }
   
   
}
1）    通过方法的第一个参数传进去
l    DAO
import java.sql.Connection;

public class TestDao {
    public void insertA(Connection con,String a,String b,……){
        …………………………………………
一系列操作
…………………………………………
    }
   
    public String queryA(Connection con,…….){
    …………………………………………
一系列操作
…………………………………………
}

    public void updateA(Connection con,…….){
        …………………………………………
一系列操作
…………………………………………
}
}

l    拦截器
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class TransactionInterceptor implements Interceptor {

    public void before(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = (Connection) invInfo.getArgs()[0];
            try {
                conn.setAutoCommit(false);
            } catch (SQLException e) {
                throw new TransactionException(e);
            }
        }
    }

    public void after(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = (Connection) invInfo.getArgs()[0];
            try {
                conn.commit();
            } catch (SQLException e) {
                throw new TransactionException(e);
            }finally{
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        throw new TransactionException(e,"Close Connection is failure!");
                    }
                }
            }
        }
    }

    public void exceptionThrow(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = (Connection) invInfo.getArgs()[0];
            try {
                conn.rollback();
            } catch (SQLException e) {
                throw new TransactionException(e);
            }finally{
                if(conn != null){
                    try {
                        conn.close();
                    } catch (SQLException e) {
                        throw new TransactionException(e,"Close Connection is failure!");
                    }
                }
            }
        }
    }
   
    private List getNeedTransaction(){
        List needTransactions = new ArrayList();
        needTransactions.add("insert");
        needTransactions.add("update");
        return needTransactions;
    }
   
    private boolean isNeedTransactions(InvokeJniInfo invInfo){
        String needTransaction = "";
        List needTransactions = getNeedTransaction();
        for(int i = 0;i            needTransaction = (String)needTransactions.get(i);
            if(invInfo.getMethod().getName().startsWith(needTransaction)){
                return true;
            }
        }
        return false;
    }
}

需要注意的是：getNeedTransaction就是需要进行事务处理的方法的开头，这个方法可以写成一个从配置文件里面去读，这里我就写死在里面了。只是对insert和update开头的方法进行事务控制。
2）    将Connection对象放在ThreadLocal中
l    ConnectionUtil类：
import java.sql.Connection;

public final class ConnectionUtil {
    private static ThreadLocal connections = new ThreadLocal();
    public static Connection getConnection(){
        Connection conn = null;
        conn = (Connection) connections.get();
        if(conn == null){
            conn = getRealConnection();
            connections.set(conn);
        }
        return conn;
    }
    public static void realseConnection(Connection conn){
        connections.set(null);
    }
    private static Connection getRealConnection() {
        实现自己获取连接的代码
        return null;
    }
}
l    DAO类
public class TestDao {
    public void insertA(String a,String b){
        Connection conn = getConnection();
        …………………………………………
一系列操作
…………………………………………
    }
        public String queryA(Connection con,…….){
        Connection conn = getConnection();
    …………………………………………
一系列操作
…………………………………………
}

    public void updateA(Connection con,…….){
Connection conn = getConnection();
        …………………………………………
一系列操作
…………………………………………
}

    private Connection getConnection(){
        return ConnectionUtil.getConnection();
    }
   
}
l    拦截器
import java.sql.Connection;
import java.sql.SQLException;
import java.util.ArrayList;
import java.util.List;

public class TransactionInterceptor implements Interceptor {

    public void before(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = getConnection();
            try {
                conn.setAutoCommit(false);
            } catch (SQLException e) {
                throw new TransactionException(e);
            }
        }
    }

    public void after(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = getConnection();
            try {
                conn.commit();
            } catch (SQLException e) {
                throw new TransactionException(e);
            }finally{
                if(conn != null){
                    try {
                        conn.close();
                        releaseConnection(conn);
                    } catch (SQLException e) {
                        throw new TransactionException(e,"Close Connection is failure!");
                    }
                }
            }
        }
    }

    public void exceptionThrow(InvokeJniInfo invInfo) {
        if(isNeedTransactions(invInfo)){
            Connection conn = getConnection();
            try {
                conn.rollback();
            } catch (SQLException e) {
                throw new TransactionException(e);
            }finally{
                if(conn != null){
                    try {
                        conn.close();
                        releaseConnection(conn);
                    } catch (SQLException e) {
                        throw new TransactionException(e,"Close Connection is failure!");
                    }
                }
            }
        }
    }
   
    private Connection getConnection(){
        return ConnectionUtil.getConnection();
    }
   
    private void releaseConnection(Connection conn){
        ConnectionUtil.releaseConnection(conn);
    }
    private List getNeedTransaction(){
        List needTransactions = new ArrayList();
        needTransactions.add("insert");
        needTransactions.add("update");
        return needTransactions;
    }
   
    private boolean isNeedTransactions(InvokeJniInfo invInfo){
        String needTransaction = "";
        List needTransactions = getNeedTransaction();
        for(int i = 0;i            needTransaction = (String)needTransactions.get(i);
            if(invInfo.getMethod().getName().startsWith(needTransaction)){
                return true;
            }
        }
        return false;
    }
}
    最后将这个拦截器添加到AOP拦截框架中去，InterceptorHandler类中的getIntercetors方法中添加一个：

    private synchronized List getIntercetors(){
        if(null == interceptors){
            interceptors = new ArrayList();
            ……………………………………
interceptors.add(new TransactionInterceptor ());
            ……………………………………
        }
        return interceptors;
}

到此全部ok！

• Java源码分析：深入探讨Iterator模式
• Java入门－－漫谈Java程序的性能优化
• ICONIX 统一建模起步之二：在开始进入设计之前
• Google小组研发模式分析
• 测试管理最佳实践