热部署 重新部署应用
热加载 重新加载class

热加载 

context.xml
< Context reloadable="true"/>

监听 class 文件改变，包括WEB-INFO/classe,WEB-INFO/lib,WEB-INFO/web.xml等文件，
若发生更改，则局部进行加载，不清空session ，不释放内存。开发中用的多，但要考虑内存溢出的情况。

监听class文件变化

Context 启动时 启动后台线程 定时运行 Loader 的  backgroundProcess

StandardContext
// The Loader implementation with which this Container is associated.
// public class WebappLoader extends LifecycleMBeanBase implements Loader, PropertyChangeListener
private Loader loader = null;

A Loader represents a Java ClassLoader implementation 
that can be used by a Container to load class files (within a repository associated with the Loader) 
that are designed to be reloaded upon request, 
as well as a mechanism to detect whether changes have occurred in the underlying repository.
 
public interface Loader {
    // Execute a periodic task, such as reloading, etc. 
    // This method will be invoked inside the classloading context of this container. 
    public void backgroundProcess();

    public ClassLoader getClassLoader();
    public Context getContext();
    
... 



    
    public void backgroundProcess() {
        if (reloadable && modified()) {
            try {
                Thread.currentThread().setContextClassLoader
                    (WebappLoader.class.getClassLoader());
                if (context != null) {
                    context.reload();
                }
            } finally {
                if (context != null && context.getLoader() != null) {
                    Thread.currentThread().setContextClassLoader
                        (context.getLoader().getClassLoader());
                }
            }
        }
    }
    
    


热部署
server.xml 
< Context docBase="xxx" path="/xxx" autoDeploy="true"/>  


< Host name="localhost"  appBase="webapps"  
            unpackWARs="true" autoDeploy="true"  
            xmlValidation="false" xmlNamespaceAware="false">  
            
整个项目重新部署，会清空session ，释放内存。 

周期事件监听器 HostConfig
public class HostConfig implements LifecycleListener 

父类 backgroundProcess
public void backgroundProcess() {
        ...
        fireLifecycleEvent(Lifecycle.PERIODIC_EVENT, null);
    }


 @Override
    public void lifecycleEvent(LifecycleEvent event) {

        // Identify the host we are associated with
        try {
            host = (Host) event.getLifecycle();
            if (host instanceof StandardHost) {
                setCopyXML(((StandardHost) host).isCopyXML());
                setDeployXML(((StandardHost) host).isDeployXML());
                setUnpackWARs(((StandardHost) host).isUnpackWARs());
                setContextClass(((StandardHost) host).getContextClass());
            }
        } catch (ClassCastException e) {
            log.error(sm.getString("hostConfig.cce", event.getLifecycle()), e);
            return;
        }

        // Process the event that has occurred
        if (event.getType().equals(Lifecycle.PERIODIC_EVENT)) {
            check();
        } else if (event.getType().equals(Lifecycle.BEFORE_START_EVENT)) {
            beforeStart();
        } else if (event.getType().equals(Lifecycle.START_EVENT)) {
            start();
        } else if (event.getType().equals(Lifecycle.STOP_EVENT)) {
            stop();
        }
    }
    
    
    /**
     * Check status of all webapps.
     */
    protected void check() {

        if (host.getAutoDeploy()) {
            // Check for resources modification to trigger redeployment
            DeployedApplication[] apps =
                deployed.values().toArray(new DeployedApplication[0]);
            for (int i = 0; i < apps.length; i++) {
                if (!isServiced(apps[i].name))
                    checkResources(apps[i], false);
            }

            // Check for old versions of applications that can now be undeployed
            if (host.getUndeployOldVersions()) {
                checkUndeploy();
            }

            // Hotdeploy applications
            deployApps();
        }
    }
   

    public void check(String name) {
        DeployedApplication app = deployed.get(name);
        if (app != null) {
            checkResources(app, true);
        }
        deployApps(name);
    }



jsp热部署

JspServlet
JspServletWrapper
JspCompilationContext
JDTCompiler
JasperLoader


public class JspServlet extends HttpServlet implements PeriodicEventListener {


public class JasperLoader extends URLClassLoader


EmbeddedServletOptions
private int modificationTestInterval = 4;


JDTCompiler 
public class JDTCompiler extends org.apache.jasper.compiler.Compiler 
isOutDated