resultSet.last(); // 游标移到最后, 获得rs长度
			int length = resultSet.getRow();
			resultSet.first(); // 还原游标到rs开头

原因: 执行的数据库查询没有查询到任何结果，却调用了resultSet.next().

2. java.sql.SQLException: 对只转发结果集的无效操作:

如果conn在创建时, 若不给定参数，预设是ResultSet.TYPE_FORWARD_ONLY、 ResultSet.CONCUR_READ_ONL, 此时不可进行游标操作, 会报错: java.sql.SQLException: 对只转发结果集的无效操作.
欲操作游标, 则应使用stmt=conn.createStatement(ResultSet.TYPE_SCROLL_INSENSITIVE, ResultSet.CONCUR_READ_ONLY);

1. Java – JDBC – MySql

1. 装好MySql, 启动服务.

2. 将mysql-connector-java-5.1.7-bin.jar 拖入WEB-INF/lib下.

搞定.

2. Java端BlazeDS配置

1. Java端:

将BlazeDS压缩包内的WEB-INF里面的东西拷贝工程内的WEB-INF下的相应位置中.[ Flex目录下有四个xml配置文件, lib下是需要使用的jar] 包括web.xm

2. 配置services-config.xml中channels标签中的内容:

                false

true
4

其中, http://localhost:8080/DepartmentManagement/ 是该Web工程的地址 [可在web-content下建立一空index.html, 运行后查看地址便可]

3. 编写Java类, 并配置remoting-config.xml文件的<service>标签下, 增加服务, 如下:

         com.insprise.guoliang.DepartmentManagement

3. Flex端建立工程

1. 建立 Flex与Java通信载体RemoteObject

为方便在整个工程中使用, 可建立一个Singleton – 关于AS中的Singleton可见: http://liguoliang.com/2008/10/128/

在该类中建立RemoteObject.

首先需要确定RemoteObject的destination, 在本例中 为”DepartmentManagement”; – 在remoting-config.xml中已配置.

其次需要确定ro的channel – 本例中为:”http://localhost:8080/DepartmentManagement/messagebroker/amf＂； － 在services-config.xml中已配置

代码:

	public static const DEFAULT_DEST:String = "DepartmentManagement";
	public static const DEFAULT_CHANNEL_URL:String = "http://localhost:8080/DepartmentManagement/messagebroker/amf";
	private static var _ro:RemoteObject;

	/**
	 * Constractor - Singleton
	 */
	 public function AppContext():void {
	 	throw new Error("AppContext is Singleton!");
	 }

	/**
	 * Get RemoteObject
	 */
	public static function getRemoteObject():RemoteObject {
		if(_ro == null) {
			_ro = createRemoteObject(DEFAULT_DEST, DEFAULT_CHANNEL_URL);
		}
		return _ro;
	}

	/**
	 * Constructs a new remote object with new channel.
	 * @param roDestination Destination of the RemoteObject; should match a destination name in the services-config.xml file.
	 * @param channelURI the URI used to create the whole endpoint URI for this channel; this uri can be relative uri (to the folder containing the SWF).
	 * @param channelId the id of the channel, if set to null, a random Id will be assigned.
	 */
	protected static function createRemoteObject(roDestination:String, channelURI:String, channelId:String = null):RemoteObject {
		var channelSet:ChannelSet = new ChannelSet();
		var channel:AMFChannel = new AMFChannel(channelId == null ? "channel-" : channelId, channelURI);	//Create new Channel
		channelSet.addChannel(channel);	

		var ro:RemoteObject = new RemoteObject(roDestination);
		ro.channelSet = channelSet;

		return ro;
	}

4 配置完成,.

在Java端建立相关的Class,

启动服务器.

在Flex端通过 Appcontext.getRemoteObject.getOperation(“方法名称”)来调用服务器端方法.

具体实例:

Java端的Class – 通过JDBC 读取 MySql中数据:

	/**
	 * Load all Department and return an ArrayList
	 * @return
	 */
	public ArrayList loadDepartments() {
		ArrayList departmentsAL = new ArrayList();
		log.info("Loading Departments...");
		try {
			//Get Connection
			Connection conn = JdbcUtilities.getConnection();
			//Create statement
			String sql = " SELECT * FROM Department d ORDER BY d.Department_ID";
			PreparedStatement ps = conn.prepareStatement(sql);

			ResultSet res = ps.executeQuery();
			log.debug("Exectuing: " + sql);
			while (res.next()) {
				int id = res.getInt("Department_ID");
				String name = res.getString("name");

				Department dp = new Department();
				dp.setId(id);
				dp.setName(name);
				departmentsAL.add(dp);
				log.debug("从数据库获得部门:  " + dp);
			}
			JdbcUtilities.closeConn(res, ps, conn);
			log.info("加载部门信息结束, 共加载部门: " + departmentsAL.size());
		} catch (Exception e) {
			log.error("SQL Error", e);
			throw new Error(e);
		}
		return departmentsAL;

	}

Flex端的代码:

		/**
	 * Load the Department's Employee
	 */

	private var op:AbstractOperation;
	public function loadEmployees():void {
		op = AppContext.getRemoteObject().getOperation("loadEmployees");	//获得Operation
		 op.arguments = [id];	//设定参数
		 var at:AsyncToken = op.send();	//Send
		 at.addResponder(this);	//为本实例增加responder

      }

Flex端responder剩余代码见:http://liguoliang.com/2009/02/777/

运行Flex工程, Flex取得RemoteObject, 然后通过channel建立到destination的连接,由Java读取数据库中信息, 并返回给Flex.

下面是恐怖的SQL:

			Statement statement = (Statement) conn.createStatement();
			String sql = "INSERT INTO `DEP`.`employee` " +
					"( `name` , `age` , `address` , `isMale` , `level` , `Department_ID` ) " +
					"VALUES (" +
					"'" + emp.getName() + "', " +
					emp.getAge()  + ", " +
					 JdbcUtilities.getSqlForString(emp.getAddress()) + ", " +
					emp.getIsMale() + ", "  +
					emp.getLevel() + ", " +
					emp.getDepartment_ID() + ");"
					;

			log.debug("Executing sql :" + sql);
			statement.executeUpdate(sql);

			ResultSet rs = statement.executeQuery("SELECT last_insert_id();");// .execute("SELECT last_insert_id();");
			if(rs.next()) {
				System.out.println(rs.getInt("1"));
			}

这里是使用PreparedStatement后的语句:

			String psql = "INSERT INTO Employee (name, age, address, isMale, level, Department_ID) VALUES (?, ?, ?, ?, ?, ?)";
			PreparedStatement ps  = conn.prepareStatement(psql,Statement.RETURN_GENERATED_KEYS);

			ps.setString(1, emp.getName());
			ps.setInt(2, emp.getAge());
			ps.setString(3, emp.getAddress());
			ps.setInt(4, emp.getIsMale());
			ps.setInt(5, emp.getLevel());
			ps.setInt(6, emp.getDepartment_ID());

			ps.executeUpdate();

			ResultSet keys = ps.getGeneratedKeys(); // equivalent to "SELECT last_insert_id();"

			if(keys.next()) {
				System.out.println(keys.getInt(1));
			}

PreparedStatement的使用步骤:

1. 声明 PreparedStatement。

   PreparedStatement prepStmt;

2. 将一条 SQL 语句指派给 PreparedStatement 对象。

   prepStmt = conn.prepareStatement(
      "INSERT INTO MyTable(MyColumn) values (?)");

3. 为该语句指派输入参数值。

   以下代码显示一个字符串参数。

   String newValue;
   // assign value
   prepStmt.setStringParameter(1, newValue);

4. 执行该语句。

   返回值表示受该语句影响的行数。

   long rowsInserted = prepStmt.executeStatement();

5. 如果禁用了 [自动提交]，请提交更改。

   conn.commit();

参考地址

获得组后插入的ID, 在上面代码中已经包括.

con.setAutoCommit(false); //关闭自动Commit
PreparedStatement updateSales = con.prepareStatement(
    "UPDATE COFFEES SET SALES = ? WHERE COF_NAME LIKE ?");
updateSales.setInt(1, 50);
updateSales.setString(2, "Colombian");
updateSales.executeUpdate();//执行Update Sales操作
PreparedStatement updateTotal = con.prepareStatement(
    "UPDATE COFFEES SET TOTAL = TOTAL + ? WHERE COF_NAME LIKE ?");
updateTotal.setInt(1, 50);
updateTotal.setString(2, "Colombian");
updateTotal.executeUpdate();//执行Update Total操作, 注意, 此二者必须同时执行成功 或同时失败.
con.commit(); //commit以上两个操作, 同时成功或失败
con.setAutoCommit(true); //将AutoCommit恢复为true

2. 务必牢记重写toString方法

3. Flex: 在跨越幅度较大, 设计Obj较多时, 使用weakreference的 Event Listener

4. 关于weakreference, 相对普通reference来说, weakreference像一个棉线, 牵着Obj – 但不妨碍garage Collection, 而普通reference则像铁链一样牢牢绑着obj, 会阻止进行garage Collection. 如果一个Object只有weak reference指向他, 则基本可以视为已经被garage Collection,

5. 可以在每个Class中加入一个Object_ID Filed, 在构造函数中使用randomNumber填充 – 便于分辨对象

6. JDBC 的 traction不是线程安全的

7. 谨慎使用ArrayCollection, Array的sort, filter功能 – 因为这会打乱其自身. 在使用其作为DataProvider时, 应使用ListCollectionView, 这样在进行操作时则其本身不会有任何改变