Filter和ThreadLocal实现事务管理

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ThreadLocal将自身和Collection绑定，在Tread的Map中以ThreadLocal为建，Collection为值，在读取时可以获取唯一的Connection链接 避免出错。

单例模式：

package com.bookStore.web;

import java.sql.Connection;

public class ConnectionContext {

    private ThreadLocal<Connection> threadLocal = new ThreadLocal<>();

    private ConnectionContext(){}

    private static ConnectionContext connectionContext = new ConnectionContext();


    public static ConnectionContext getInstance(){
        return connectionContext;
    }

    public void bind(Connection connection){
        threadLocal.set(connection);
    }

    public Connection get(){
        return threadLocal.get();
    }

    public void remove(){
        threadLocal.remove();
    }
}

Filter代码：

public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {

        Connection connection = null;

        try {
            connection = JDBCUtils.getConnection();

            connection.setAutoCommit(false);

            ConnectionContext.getInstance().bind(connection);

            chain.doFilter(request, response);

            connection.commit();

        } catch (Exception e) {
            e.printStackTrace();
            System.out.println("捕获成功！");
            try {
                connection.rollback();
                System.out.println("回滚成功");
            } catch (SQLException e1) {
                System.out.println("回滚失败。");
                // TODO Auto-generated catch block
                e1.printStackTrace();
            }

            HttpServletRequest req = (HttpServletRequest) request;
            HttpServletResponse res = (HttpServletResponse) response;


            res.sendRedirect(req.getContextPath()+"/error-1.jsp");
            return;
        }   finally {
            ConnectionContext.getInstance().remove();
            JDBCUtils.release(connection);
        }


    }

注意: StringBuffer 使用 equals 时 要转成 String
stringBuffer.toString().equals();