WebLogicRMI与JMS的深入解析

### WebLogic RMI与JMS的深入解析 #### 1. WebLogic RMI的应用与特性 在证券系统中，我们有不同的客户端和服务器协同工作。`MarketMakerClient` 负责设置价格，`QuoteClient` 用于获取报价，`PriceServerImpl` 作为RMI服务器处理客户端请求。以下是 `QuoteClient` 和 `PriceServerImpl` 的输出示例： **QuoteClient输出示例** ```plaintext QuoteClient started. QuoteClient getting quotes. Quote time: Mon Apr 30 13:33:44 PDT 2001 Security: SUNW Price: 20.25 Security: INTC Price: 30.5 Security: BEAS Price: 39.75 QuoteClient getting quotes. Quote time: Mon Apr 30 13:34:04 PDT 2001 Security: SUNW Price: 20.5 Security: INTC Price: 30.25 Security: BEAS Price: 40 ``` **PriceServerImpl输出示例** ```plaintext PriceServer: Call to setPrice for SUNW to 20.25 PriceServer: Call to setPrice for INTC to 30.5 PriceServer: Call to setPrice for BEAS to 39.75 PriceServer: Call to getPrice for symbol : SUNW PriceServer: Call to getPrice for symbol : INTC PriceServer: Call to getPrice for symbol : BEAS PriceServer: Call to setPrice for SUNW to 20.5 PriceServer: Call to setPrice for INTC to 30.25 PriceServer: Call to setPrice for BEAS to 40 PriceServer: Call to getPrice for symbol : SUNW PriceServer: Call to getPrice for symbol : INTC PriceServer: Call to getPrice for symbol : BEAS ``` ##### 1.1 单向通信的局限与双向通信的引入 当前的架构中，客户端到服务器的通信是单向的。这种架构在大多数情况下可行，但存在一些弱点。例如，当客户端调用服务器上的长时间运行方法时，如果是同步调用，客户端线程会被阻塞直到服务器方法返回；如果是异步调用，客户端无法得知服务器方法何时完成。 为了解决这个问题，引入了 `TradingClient`。`TradingClient` 会异步地向 `PriceServerImpl` 下达股票市场订单。`PriceServerImpl` 在人为延迟后执行订单，并通知 `TradingClient` 订单执行情况，这就需要 `PriceServerImpl` 和 `TradingClient` 之间进行双向通信。 ```mermaid graph LR classDef startend fill:#F5EBFF,stroke:#BE8FED,stroke-width:2px; classDef process fill:#E5F6FF,stroke:#73A6FF,stroke-width:2px; A([TradingClient]):::startend -->|异步下订单| B([PriceServerImpl]):::startend B -->|通知订单执行情况| A ``` ##### 1.2 订单和执行信息的传输 为了实现双向通信，创建了 `Order` 和 `Execution` 两个类，它们需要实现 `java.io.Serializable` 接口，以便通过RMI传输。 ```java public class Order implements java.io.Serializable { private int number; // unique order number private String symbol; // ticker symbol private int shares; // number of shares to purchase // plus method definitions } public class Execution implements java.io.Serializable { private int number; // copied from order number private String symbol; // ticker symbol private int shares; // number of shares purchased private float price; // price per share at execution // plus method definitions } ``` ##### 1.3 TradingClient的实现 `TradingClient` 继承自 `java.util.TimerTask`，每30秒提交一个新订单。以下是提交订单的代码： ```java // Get the list of securities managed by the server. String securities[] = server.getSecurities(); // Create a new Order instance Order order = new Order(); Random rand = new Random(); // Increment the order number order.setNumber(++orderNumber); // Choose one of the available securities at random order.setSymbol(securities[rand.nextInt(securities.length)]); // Choose a random number of shares order.setShares(rand.nextInt(1000) + 1); // Enter the order via a remote call to the server. // Pass a reference to ourselves so the server can call back. server.enterMarketOrder(order, this); ``` ##### 1.4 PriceServerImpl的实现 `PriceServerImpl` 的 `enterMarketOrder` 方法异步处理订单，它会启动一个新线程来执行订单。 ```java public void enterMarketOrder(Order order, ExecutionAlert clientRef) { // Receives an order from a client, and also a // reference to the client. Spawns a new thread // to execute the trade (which may take some time), // then returns. System.out.println("A client has placed an order!"); System.out.println("Time: " + new Date()); System.out.println(order + "\n"); DoExecution exec = new DoExecution(order, clientRef); new Thread(exec).start(); } // Inner class to handle order executions. private class DoExecution implements Runnable { private Order order; private ExecutionAlert client; public DoExecution(Order ord, ExecutionAlert clientRef) { order = ord; client = clientRef; } public void run() { try { // Wait 10 seconds to simulate submission of the order // to a stock exchange. Thread.currentThread().sleep(10000); // Create an Execution instance and execute the order. Execution execution = new Execution(); // Copy order data into the execution. execution.setNumber(order.getNumber()); execution.setSymbol(order.getSymbol()); execution.setShares(order.getShares()); // Execute at the stock’s current price and write a // status message to standard output. execution.setPrice(getPrice(order.getSymbol())); System.out.println("An order has been executed!"); System.out.println("Time: " + new Date()); System.out.println(execution + "\n"); // Make a remote call to the client to notify them // of the execution. client.notifyOfExecution(execution); } catch (Exception e) { e.printStackTrace(); } } } ``` #### 2. 客户端方法的调用与注册 `TradingClient` 的 `notifyOfExecution` 方法只是简单地将订单执行信息输出到标准输出。 ```java public void notifyOfExecution(Execution exec) { System.out.println("An order has been executed!"); System.out.println("Time: " + new Date()); System.out.println(exec + "\n"); } ``` 客户端可以实现扩展 `weblogic.rmi.remote` 的接口，并在WebLogic的类路径中提供客户端远程方法的存根，这样客户端之间或服务器就可以调用这些方法。 也可以将 `TradingClient` 注册到RMI注册表中： ```java TradingClient client = new TradingClient(); Context ctx = Environment.getInitialContext(); ctx.bind("TradingClient", client); System.out.println("TradingClient was started and bound " + "in the registry to the name " + "TradingClient"); ``` 从另一个客户端调用 `TradingClient` 的远程方法： ```java InitialContext ctx = Environment.getInitialContext(); ExecutionAlert tc = (ExecutionAlert) ctx.lookup("TradingClient"); Execution exec = new Execution(); tc.notifyOfExecution(exec); ``` #### 3. 从RMI服务器调用EJB 在设计中引入了会话EJB `ExecuteTrade`，将执行代码从 `PriceServerImpl` 移到 `ExecuteTrade` 中。 ```java public void enterMarketOrder(Order order, ExecutionAlert client) { try { // Create a context with which to lookup ```