释义所谓热部署,就是在应用正在运行的时候升级软件,却不需要重新启动应用。
对于Java应用程序来说,热部署就是在运行时更新Java类文件。在基于Java的应用服务器实现热部署的过程中,类装入器扮演着重要的角色。大多数基于Java的应用服务器,包括EJB服务器和Servlet容器,都支持热部署。类装入器不能重新装入一个已经装入的类,但只要使用一个新的类装入器实例,就可以将类再次装入一个正在运行的应用程序。Tomcat的热部署Tomcat的热部署(以后就不用重启了)
没有热部署和有热部署的开发效率是天差地别的。这个问题还受很多第三方软件包(Struts,Spring,Hibernate)的限制。本来可以热部署,加入了第三方的包就不可以了。所以,先说明详细的软件环境,和程序配置是非常必要的。
虚拟机:java version "1.5.0_06"
Servlet Engine:Apache Tomcat/5.0.27
Eclipse:3.0.1
Myeclipse:3.8.3
应用程序情况:纯正的sertlet+jsp+javabean,数据库连接使用JDBC-ODBC桥连接Access数据库。没有使用任何第三方软件包,没有使用Struts,Spring,Hibernate。WebRootWEB-INFlib下是空的。
配置方法:
ie登陆http://Tomcat所在的服务器IP:8080/ -> 点超连接“Tomcat Administration”-> 输入用户名密码登陆 ->在左侧的功能树中 -> Tomcat Server -> Service(Catalina) -> Host(localhost) -> Context(/要修改的web项目) ->右侧新出现的页面中 ->Reloadable设置为true -> Save按钮 -> Commit Changes。
然后Tomcat日志显示:
debugging -- changes saved to conf/server.xml
- Removing web application at context path /test
- Processing Context configuration file URL file:D:Program FilesTomcat 5.0confCatalinalocalhostest.xml
- Removing web application at context path /admin
- unregistering logger Catalina:type=Logger,path=/admin,host=localhost
- Processing Context configuration file URL file:D:Program FilesTomcat 5.0confCatalinalocalhostadmin.xml
- Initializing, config='org.apache.struts.util.LocalStrings', returnNull=true
- Initializing, config='org.apache.struts.action.ActionResources', returnNull=true
- Initializing, config='org.apache.webapp.admin.ApplicationResources', returnNull=true
- Removing web application at context path /webdav
- Processing Context configuration file URL file:D:Program FilesTomcat 5.0confCatalinalocalhostwebdav.xml
- Removing web application at context path /test
- Processing Context configuration file URL file:D:Program FilesTomcat 5.0confCatalinalocalhostest.xml
……
这样,设置就生效了。
开发时,修改.java文件后,调用这个类时日志提示:
- Reloading this Context has started
这是正在重新加载修改后的.class文件。
如果没有进行这个设置,修改.java文件后,不抛出异常。系统使用没有修改的.java文件继续运行。
不同版本的Tomcat的配置方法是不同的。这里使用的是5.0.27
j2ee开发插件(这里使用Myeclipse),也可能导致热部署失效。因为插件必须要把编译好的.class文件从工作空间复制到Tomcatwebapps下的项目里。才能使Tomcat得到需要热部署的文件。
注意:如果项目中加入了Struts,Hibernate,Spring只类的第三方软件,可能导致热部署失效。java热部署的简单例子我的目录结构是
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:hotdeployserverServerImpl.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:hotdeployserverServerImpl.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。