java热部署的简单例子

本文纯粹就是将一篇英文文章的一个段落翻译一下，并将例子跑通。

原文出处：http://java.sun.com/developer/TechTips/2000/tt1027.html

我的目录结构是

d://hotdeploy//Client.java

d://hotdeploy//ServerItf.java

d://hotdeploy//server//ServerImpl.java

文件内容依次为：

//file Client.java
import java.net.URL;
import java.net.URLClassLoader;
import java.io.BufferedReader;
import java.io.InputStreamReader;

public class Client {
static ClassLoader cl;

static ServerItf server;

public static void loadNewVersionOfServer() throws Exception {
URL[] serverURLs = new URL[] { new URL("file://d:/hotdeploy/server/") };
cl = new URLClassLoader(serverURLs);
server = (ServerItf) cl.loadClass("ServerImpl").newInstance();
}

public static void test() throws Exception {
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
loadNewVersionOfServer();
while (true) {
System.out.print("Enter QUOTE, RELOAD, GC, or QUIT: ");
String cmdRead = br.readLine();
String cmd = cmdRead.toUpperCase();
if (cmd.equals("QUIT")) {
return;
} else if (cmd.equals("QUOTE")) {
System.out.println(server.getQuote());
} else if (cmd.equals("RELOAD")) {
loadNewVersionOfServer();
} else if (cmd.equals("GC")) {
System.gc();
System.runFinalization();
}
}
}

public static void main(String[] args) {
try {
test();
} catch (Exception e) {
e.printStackTrace();
}
}
}

-------------------------------------------------------------------------

public interface ServerItf {
public String getQuote();
}

-------------------------------------------------------------------------

public class ServerImpl implements ServerItf {

// catch the class being unloaded from the VM
static Object reporter = new Reporter(ServerImpl.class);

public String getQuote() {
return "i love you";
}
}

// file ServerImpl.java. Place this file
// in a subdirectory named 'server'.
class Reporter {
Class cls;

Reporter(Class cls) {
this.cls = cls;
System.out.println("ServerImpl class " + cls.hashCode()
+ " loaded into VM");
}

protected void finalize() {
System.out.println("ServerImpl class " + cls.hashCode()
+ " unloaded from VM");
}
}

-------------------------------------------------------------------------

运行的命令依次为：

D:/hotdeploy>javac Client.java

D:/hotdeploy>javac ServerItf.java

D:/hotdeploy>javac -cp d:/hotdeploy d:/hotdeploy/server/ServerImpl.java

D:/hotdeploy>java Client
ServerImpl class 1641745 loaded into VM
Enter QUOTE, RELOAD, GC, or QUIT: quote
i love you
Enter QUOTE, RELOAD, GC, or QUIT:

-------------------------------------------------------------------------

编辑ServerImpl.java为：

public class ServerImpl implements ServerItf {

// catch the class being unloaded from the VM
static Object reporter = new Reporter(ServerImpl.class);

public String getQuote() {
return "you love me";
}
}

// file ServerImpl.java. Place this file
// in a subdirectory named 'server'.
class Reporter {
Class cls;

Reporter(Class cls) {
this.cls = cls;
System.out.println("ServerImpl class " + cls.hashCode()
+ " loaded into VM");
}

protected void finalize() {
System.out.println("ServerImpl class " + cls.hashCode()
+ " unloaded from VM");
}
}

-------------------------------------------------------------------------

打开另外一个dos窗口，运行javac -cp d:/hotdeploy d:/hotdeploy/server/ServerImpl.java

-------------------------------------------------------------------------

回到原先的doc窗口，依次运行

Enter QUOTE, RELOAD, GC, or QUIT: reload
ServerImpl class 12677476 loaded into VM
Enter QUOTE, RELOAD, GC, or QUIT: quote
you love me
Enter QUOTE, RELOAD, GC, or QUIT:

可以看到效果。