文件存入MYSql表的blob

向MYSql的数据表中存入文件，这看似没有什么大问题，只要把文件存入longblob字段就行了。但是最近的实践发现看似简单的背后其实有很多陷阱。下面就来分享一下我遇到的问题及我的解决办法。

先介绍一下我的应用，只有两个页面upload.jsp和download.jsp。upload.jsp使用common file upload来上传文件，并将文件存入mysql的数据表的longblob字段。download.jsp则是从数据库中取出该longblob字段的内容，并写到浏览器客户端。数据库的连接我选用tomcat的连接池，url为jdbc:mysql://localhost:3306/test?characterEncoding=gbk。jsp页面的编码都为gbk。数据表的结构如下

CREATE TABLE `file` (
		`id` int(11) NOT NULL AUTO_INCREMENT,
		`filename` varchar(255) CHARACTER SET utf8 NOT NULL,
		`content` longblob,
		`filetype` varchar(255) CHARACTER SET utf8 NOT NULL,
		`size` int(11) DEFAULT NULL,
		`ip` varchar(255) CHARACTER SET utf8 NOT NULL,
		`date` timestamp NOT NULL DEFAULT '0000-00-00 00:00:00' ON UPDATE 			CURRENT_TIMESTAMP,
		PRIMARY KEY (`id`)
	) ENGINE=InnoDB AUTO_INCREMENT=15 DEFAULT CHARSET=gbk

  上传文件的java代码如下

request.setCharacterEncoding("gbk");
	if("POST".equalsIgnoreCase(request.getMethod())){
		DiskFileUpload upload = new DiskFileUpload();
		upload.setHeaderEncoding("gbk");
		List<FileItem> list = upload.parseRequest(request);
		
		for(FileItem fileItem : list){
			if(!fileItem.isFormField()){
				String filename = fileItem.getName().replace("\\", "/");
				filename = filename.substring(filename.lastIndexOf("/") + 1);
				
				Context envContext = (Context)new InitialContext().lookup("java:/comp/env");
				DataSource ds = (DataSource) envContext.lookup("mysqlTest");
				Connection conn = ds.getConnection();
				PreparedStatement preStmt = conn.prepareStatement("insert into file (filename, filetype, size, content, ip, date) values (?,?,?,?,?,?)");
				preStmt.setString(1, filename);
				preStmt.setString(2, fileItem.getContentType());
				preStmt.setInt(3, (int)fileItem.getSize());
				preStmt.setString(5, request.getRemoteAddr());
				preStmt.setTimestamp(6, new Timestamp(System.currentTimeMillis()));
				preStmt.setBinaryStream(4, fileItem.getInputStream(),(int)fileItem.getSize());
				
				preStmt.executeUpdate();
				preStmt.close();
				conn.close();
			}
		}
	}

 下载文件的代码如下

Context envContext = (Context)new InitialContext().lookup("java:/comp/env");
		DataSource ds = (DataSource) envContext.lookup("mysqlTest");
		conn = ds.getConnection();
		preStmt = conn.prepareStatement("select * from file where id = ?");
		preStmt.setInt(1, id);
		
		rs = preStmt.executeQuery();
		
		if(rs.next()){
			response.reset();
			response.setContentType(rs.getString("filetype"));
			response.setContentLength(rs.getInt("size"));
			
			InputStream ins = null;
			OutputStream ous = null;
			
			try{
				ins = rs.getBinaryStream("content");
				ous = response.getOutputStream();
				byte[] b = new byte[1024];
				int len = 0;
				while((len = ins.read(b))!= -1){
					ous.write(b, 0, len);
				}
			}finally{
				if(ous != null) ous.close();
				if(ins != null) ins.close();
			}

 开始上传一些文本文件没问题，但是当上传的文件大于1M时就报出如下异常

com.mysql.jdbc.PacketTooBigException: Packet for query is too large (5553258 > 1048576). You can change this value on the server by setting the max_allowed_packet' variable.
	com.mysql.jdbc.MysqlIO.send(MysqlIO.java:3279)
	com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1971)
	com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2151)
	com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2625)
	com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2119)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2415)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2333)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2318)
	org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:105)
	org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:105)
	org.apache.jsp.saveFile2Mysql_jsp._jspService(saveFile2Mysql_jsp.java:111)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

 为了解决这个问题，没少废了周折。在网上看到一些解决办法，但是在我这都不起作用。在Mysql的安装装目录的my.ini文件的【mysqld】节点下添加max_allowed_packet=100M，重启mysql服务后（可用net stop/start mysql），在mysql客户端查看时show variables llike “%packet%”，显示max_allowed_packet 的大小依然是1M。用mysqld --max_allowed_packet=100M结果依然如此。经过不断尝试发现了一个问题mysqld启动后会成为一个后台运行的进程，当已经有一个mysqld进程在运行时，再次调用mysqld将会被忽略。所以正确的做法是，首先关闭mysql服务，然后查看windows的任务管理器，关闭正在运行的mysqld进程（如果存在），然后再用mysqld --max_allowed_packet=100M来启动就没有问题了。然而这个办法在机器重启之后就没有效果了，开机启动所使用的max_allowed_packet如何改没有找到解决办法。

解决了上个问题，在上传MP3文件时又遇到了一个异常，同样让人头痛，异常信息如下

com.mysql.jdbc.exceptions.jdbc4.MySQLSyntaxErrorException: You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for
the right syntax to use near '焲拲è¬�?鞱覑?Y:r8閧釥\"R㈧?^薇覆皟箧统廜矻剭愦;äº é‚ªè¶‘t>' at line 1
	sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
	sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
	java.lang.reflect.Constructor.newInstance(Constructor.java:513)
	com.mysql.jdbc.Util.handleNewInstance(Util.java:411)
	com.mysql.jdbc.Util.getInstance(Util.java:386)
	com.mysql.jdbc.SQLError.createSQLException(SQLError.java:1052)
	com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3597)
	com.mysql.jdbc.MysqlIO.checkErrorPacket(MysqlIO.java:3529)
	com.mysql.jdbc.MysqlIO.sendCommand(MysqlIO.java:1990)
	com.mysql.jdbc.MysqlIO.sqlQueryDirect(MysqlIO.java:2151)
	com.mysql.jdbc.ConnectionImpl.execSQL(ConnectionImpl.java:2625)
	com.mysql.jdbc.PreparedStatement.executeInternal(PreparedStatement.java:2119)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2415)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2333)
	com.mysql.jdbc.PreparedStatement.executeUpdate(PreparedStatement.java:2318)
	org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:105)
	org.apache.tomcat.dbcp.dbcp.DelegatingPreparedStatement.executeUpdate(DelegatingPreparedStatement.java:105)
	org.apache.jsp.saveFile2Mysql_jsp._jspService(saveFile2Mysql_jsp.java:111)
	org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)

 查资料发现问题的根源在连接数据库时使用的字符编码，将url由 jdbc:mysql://localhost:3306/test?characterEncoding=gbk改成url为jdbc:mysql://localhost:3306/test?characterEncoding=utf8问题就解决了。