Ò»¡¢Ê²Ã´ÊÇClassLoader?
´ó¼Ò¶¼ÖªµÀ£¬µ±ÎÒÃÇдºÃÒ»¸öJava³ÌÐòÖ®ºó£¬²»ÊǹÜÊÇCS»¹ÊÇBSÓ¦Ó㬶¼ÊÇÓÉÈô¸É¸ö.classÎļþ×éÖ¯¶ø³ÉµÄÒ»¸öÍêÕûµÄJavaÓ¦ÓóÌÐò£¬µ±³ÌÐòÔÚÔËÐÐʱ£¬¼´»áµ÷ÓøóÌÐòµÄÒ»¸öÈë¿Úº¯ÊýÀ´µ÷ÓÃϵͳµÄÏà¹Ø¹¦ÄÜ£¬¶øÕâЩ¹¦Äܶ¼±»·â×°ÔÚ²»Í¬µÄclassÎļþµ±ÖУ¬ËùÒÔ¾³£Òª´ÓÕâ¸öclassÎļþÖÐÒªµ÷ÓÃÁíÍâÒ»¸öclassÎļþÖеķ½·¨£¬Èç¹ûÁíÍâÒ»¸öÎļþ²»´æÔڵģ¬Ôò»áÒý·¢ÏµÍ³Òì³£¡£¶ø³ÌÐòÔÚÆô¶¯µÄʱºò£¬²¢²»»áÒ»´ÎÐÔ¼ÓÔØ³ÌÐòËùÒªÓõÄËùÓÐclassÎļþ£¬¶øÊǸù¾Ý³ÌÐòµÄÐèÒª£¬Í¨¹ýJavaµÄÀà¼ÓÔØ»úÖÆ£¨ClassLoader£©À´¶¯Ì¬¼ÓÔØÄ³¸öclassÎļþµ½ÄÚ´æµ±Öе쬴ӶøÖ»ÓÐclassÎļþ±»ÔØÈëµ½ÁËÄÚ´æÖ®ºó£¬²ÅÄܱ»ÆäËüclassËùÒýÓá£ËùÒÔClassLoader¾ÍÊÇÓÃÀ´¶¯Ì¬¼ÓÔØclassÎļþµ½ÄÚ´æµ±ÖÐÓõġ£
¶þ¡¢JavaĬÈÏÌṩµÄÈý¸öClassLoader
BootStrap ClassLoader£º³ÆÎªÆô¶¯Àà¼ÓÔØÆ÷£¬ÊÇJavaÀà¼ÓÔØ²ã´ÎÖÐ×î¶¥²ãµÄÀà¼ÓÔØÆ÷£¬¸ºÔð¼ÓÔØJDKÖеĺËÐÄÀà¿â£¬È磺rt.jar¡¢resources.jar¡¢charsets.jarµÈ£¬¿Éͨ¹ýÈçϳÌÐò»ñµÃ¸ÃÀà¼ÓÔØÆ÷´ÓÄÄЩµØ·½¼ÓÔØÁËÏà¹ØµÄjar»òclassÎļþ£º
URL[] urls = sun.misc.Launcher.getBootstrapClassPath().getURLs(); for (int i = 0; i < urls.length; i++) { System.out.println(urls[i].toExternalForm()); } |
ÒÔÏÂÄÚÈÝÊÇÉÏÊö³ÌÐò´Ó±¾»úJDK»·¾³Ëù»ñµÃµÄ½á¹û£º
file: /C:/Program%20Files/ Java/jdk1.6.0_22/jre/lib/resources.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/rt.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/sunrsasign.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/jsse.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/jce.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/lib/charsets.jar
file: /C:/Program%20Files/Java/jdk1.6.0_22/jre/classes/ |
ÆäʵÉÏÊö½á¹ûÒ²ÊÇͨ¹ý²éÕÒsun.boot.class.pathÕâ¸öϵͳÊôÐÔËùµÃÖªµÄ¡£
System.out.println(System.getProperty ("sun.boot.class.path"));
|
´òÓ¡½á¹û£º
C:\Program Files\Java\jdk1.6.0_22\jre\lib\resources.jar; C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar; C:\Program Files\Java\jdk1.6.0_22\jre\lib\sunrsasign. <>jar;C:\Program Files\Java\jdk1.6.0_22\jre\lib\jsse.jar; C:\Program Files\Java\jdk1.6.0_22\jre\lib\jce.jar; C:\Program Files\Java\jdk1.6.0_22\jre\lib\charsets.jar; C:\Program Files\Java\jdk1.6.0_22\jre\classes
|
Extension ClassLoader£º³ÆÎªÀ©Õ¹Àà¼ÓÔØÆ÷£¬¸ºÔð¼ÓÔØJavaµÄÀ©Õ¹Àà¿â£¬Ä¬ÈϼÓÔØJAVA_HOME/jre/lib/ext/ĿϵÄËùÓÐjar¡£
App ClassLoader£º³ÆÎªÏµÍ³Àà¼ÓÔØÆ÷£¬¸ºÔð¼ÓÔØÓ¦ÓóÌÐòclasspathĿ¼ÏµÄËùÓÐjarºÍclassÎļþ¡£
×¢Ò⣺ ³ýÁËJavaĬÈÏÌṩµÄÈý¸öClassLoaderÖ®Í⣬Óû§»¹¿ÉÒÔ¸ù¾ÝÐèÒª¶¨Òå×ÔÒѵÄClassLoader£¬¶øÕâЩ×Ô¶¨ÒåµÄClassLoader¶¼±ØÐë¼Ì³Ð×Ôjava.lang.ClassLoaderÀ࣬Ҳ°üÀ¨JavaÌṩµÄÁíÍâ¶þ¸öClassLoader£¨Extension
ClassLoaderºÍApp ClassLoader£©ÔÚÄÚ£¬µ«ÊÇBootstrap ClassLoader²»¼Ì³Ð×ÔClassLoader£¬ÒòΪËü²»ÊÇÒ»¸öÆÕͨµÄJavaÀ࣬µ×²ãÓÉC++±àд£¬ÒÑǶÈëµ½ÁËJVMÄں˵±ÖУ¬µ±JVMÆô¶¯ºó£¬Bootstrap
ClassLoaderÒ²Ëæ×ÅÆô¶¯£¬¸ºÔð¼ÓÔØÍêºËÐÄÀà¿âºó£¬²¢¹¹ÔìExtension ClassLoaderºÍApp
ClassLoaderÀà¼ÓÔØÆ÷¡£
Èý¡¢ClassLoader¼ÓÔØÀàµÄÔÀí
1¡¢ÔÀí½éÉÜ
ClassLoaderʹÓõÄÊÇË«Ç×ίÍÐÄ£ÐÍÀ´ËÑË÷ÀàµÄ£¬Ã¿¸öClassLoaderʵÀý¶¼ÓÐÒ»¸ö¸¸Àà¼ÓÔØÆ÷µÄÒýÓ㨲»ÊǼ̳еĹØÏµ£¬ÊÇÒ»¸ö°üº¬µÄ¹ØÏµ£©£¬ÐéÄâ»úÄÚÖõÄÀà¼ÓÔØÆ÷£¨Bootstrap
ClassLoader£©±¾ÉíûÓи¸Àà¼ÓÔØÆ÷£¬µ«¿ÉÒÔÓÃ×÷ÆäËüClassLoaderʵÀýµÄµÄ¸¸Àà¼ÓÔØÆ÷¡£µ±Ò»¸öClassLoaderʵÀýÐèÒª¼ÓÔØÄ³¸öÀàʱ£¬Ëü»áÊÔͼÇ××ÔËÑË÷ij¸öÀà֮ǰ£¬ÏȰÑÕâ¸öÈÎÎñίÍиøËüµÄ¸¸Àà¼ÓÔØÆ÷£¬Õâ¸ö¹ý³ÌÊÇÓÉÉÏÖÁÏÂÒÀ´Î¼ì²éµÄ£¬Ê×ÏÈÓÉ×î¶¥²ãµÄÀà¼ÓÔØÆ÷Bootstrap
ClassLoaderÊÔͼ¼ÓÔØ£¬Èç¹ûû¼ÓÔØµ½£¬Ôò°ÑÈÎÎñת½»¸øExtension ClassLoaderÊÔͼ¼ÓÔØ£¬Èç¹ûҲû¼ÓÔØµ½£¬Ôòת½»¸øApp
ClassLoader ½øÐмÓÔØ£¬Èç¹ûËüҲûÓмÓÔØµÃµ½µÄ»°£¬Ôò·µ»Ø¸øÎ¯Íеķ¢ÆðÕߣ¬ÓÉËüµ½Ö¸¶¨µÄÎļþϵͳ»òÍøÂçµÈURLÖмÓÔØ¸ÃÀà¡£Èç¹ûËüÃǶ¼Ã»ÓмÓÔØµ½Õâ¸öÀàʱ£¬ÔòÅ׳öClassNotFoundExceptionÒì³£¡£·ñÔò½«Õâ¸öÕÒµ½µÄÀàÉú³ÉÒ»¸öÀàµÄ¶¨Ò壬²¢½«Ëü¼ÓÔØµ½ÄÚ´æµ±ÖУ¬×îºó·µ»ØÕâ¸öÀàÔÚÄÚ´æÖеÄClassʵÀý¶ÔÏó¡£
2¡¢ÎªÊ²Ã´ÒªÊ¹ÓÃË«Ç×ίÍÐÕâÖÖÄ£ÐÍÄØ£¿
ÒòΪÕâÑù¿ÉÒÔ±ÜÃâÖØ¸´¼ÓÔØ£¬µ±¸¸Ç×ÒѾ¼ÓÔØÁ˸ÃÀàµÄʱºò£¬¾ÍûÓбØÒª×ÓClassLoaderÔÙ¼ÓÔØÒ»´Î¡£¿¼Âǵ½°²È«ÒòËØ£¬ÎÒÃÇÊÔÏëһϣ¬Èç¹û²»Ê¹ÓÃÕâÖÖίÍÐģʽ£¬ÄÇÎÒÃǾͿÉÒÔËæÊ±Ê¹ÓÃ×Ô¶¨ÒåµÄStringÀ´¶¯Ì¬Ìæ´újavaºËÐÄapiÖж¨ÒåµÄÀàÐÍ£¬ÕâÑù»á´æÔڷdz£´óµÄ°²È«Òþ»¼£¬¶øË«Ç×ίÍеķ½Ê½£¬¾Í¿ÉÒÔ±ÜÃâÕâÖÖÇé¿ö£¬ÒòΪStringÒѾÔÚÆô¶¯Ê±¾Í±»Òýµ¼Àà¼ÓÔØÆ÷£¨Bootstrcp
ClassLoader£©¼ÓÔØ£¬ËùÒÔÓû§×Ô¶¨ÒåµÄClassLoaderÓÀÔ¶Ò²ÎÞ·¨¼ÓÔØÒ»¸ö×Ô¼ºÐ´µÄString£¬³ý·ÇÄã¸Ä±äJDKÖÐClassLoaderËÑË÷ÀàµÄĬÈÏËã·¨¡£
3¡¢ µ«ÊÇJVMÔÚËÑË÷ÀàµÄʱºò£¬ÓÖÊÇÈçºÎÅж¨Á½¸öclassÊÇÏàͬµÄÄØ£¿
JVMÔÚÅж¨Á½¸öclassÊÇ·ñÏàͬʱ£¬²»½öÒªÅжÏÁ½¸öÀàÃûÊÇ·ñÏàͬ£¬¶øÇÒÒªÅжÏÊÇ·ñÓÉͬһ¸öÀà¼ÓÔØÆ÷ʵÀý¼ÓÔØµÄ¡£Ö»ÓÐÁ½ÕßͬʱÂú×ãµÄÇé¿öÏ£¬JVM²ÅÈÏΪÕâÁ½¸öclassÊÇÏàͬµÄ¡£¾ÍËãÁ½¸öclassÊÇͬһ·Ýclass×Ö½ÚÂ룬Èç¹û±»Á½¸ö²»Í¬µÄClassLoaderʵÀýËù¼ÓÔØ£¬JVMÒ²»áÈÏΪËüÃÇÊÇÁ½¸ö²»Í¬class¡£±ÈÈçÍøÂçÉϵÄÒ»¸öJavaÀàorg.classloader.simple.NetClassLoaderSimple£¬javac±àÒëÖ®ºóÉú³É×Ö½ÚÂëÎļþNetClassLoaderSimple.class£¬ClassLoaderAºÍClassLoaderBÕâÁ½¸öÀà¼ÓÔØÆ÷²¢¶ÁÈ¡ÁËNetClassLoaderSimple.classÎļþ£¬²¢·Ö±ð¶¨Òå³öÁËjava.lang.ClassʵÀýÀ´±íʾÕâ¸öÀ࣬¶ÔÓÚJVMÀ´Ëµ£¬ËüÃÇÊÇÁ½¸ö²»Í¬µÄʵÀý¶ÔÏ󣬵«ËüÃÇȷʵÊÇͬһ·Ý×Ö½ÚÂëÎļþ£¬Èç¹ûÊÔͼ½«Õâ¸öClassʵÀýÉú³É¾ßÌåµÄ¶ÔÏó½øÐÐת»»Ê±£¬¾Í»áÅ×ÔËÐÐʱÒì³£java.lang.ClassCaseException£¬ÌáʾÕâÊÇÁ½¸ö²»Í¬µÄÀàÐÍ¡£ÏÖÔÚͨ¹ýʵÀýÀ´ÑéÖ¤ÉÏÊöËùÃèÊöµÄÊÇ·ñÕýÈ·£º
1£©¡¢ÔÚweb·þÎñÆ÷ÉϽ¨Ò»¸öorg.classloader.simple.NetClassLoaderSimple.javaÀà
package org.classloader.simple;
public class NetClassLoaderSimple {
private NetClassLoaderSimple instance;
public void setNetClassLoaderSimple(Object
obj) {
this.instance = (NetClassLoaderSimple)obj;
}
}
org.classloader.simple.NetClassLoaderSimpleÀàµÄsetNetClassLoaderSimple·½·¨½ÓÊÕÒ»¸öObjectÀàÐͲÎÊý£¬²¢½«ËüÇ¿ÖÆ×ª»»³Éorg.classloader.simple.NetClassLoaderSimpleÀàÐÍ¡£
|
2£©¡¢²âÊÔÁ½¸öclassÊÇ·ñÏàͬ£¨NetWorkClassLoader.java£©
package classloader;
public class NewworkClassLoaderTest {
public static void main(String[] args) {
try {
//²âÊÔ¼ÓÔØÍøÂçÖеÄclassÎļþ
String rootUrl = "http://localhost:8080/httpweb/classes";
String className = "org.classloader.simple.NetClassLoaderSimple";
NetworkClassLoader ncl1 = new NetworkClassLoader(rootUrl);
NetworkClassLoader ncl2 = new NetworkClassLoader(rootUrl);
Class<?> clazz1 = ncl1.loadClass(className);
Class<?> clazz2 = ncl2.loadClass(className);
Object obj1 = clazz1.newInstance();
Object obj2 = clazz2.newInstance();
clazz1.getMethod("setNetClassLoaderSimple",
Object.class).invoke(obj1, obj2);
} catch (Exception e) {
e.printStackTrace();
}
}
} |
Ê×ÏÈ»ñµÃÍøÂçÉÏÒ»¸öclassÎļþµÄ¶þ½øÖÆÃû³Æ£¬È»ºóͨ¹ý×Ô¶¨ÒåµÄÀà¼ÓÔØÆ÷NetworkClassLoader´´½¨Á½¸öʵÀý£¬²¢¸ù¾ÝÍøÂçµØÖ··Ö±ð¼ÓÔØÕâ·Ýclass£¬²¢µÃµ½ÕâÁ½¸öClassLoaderʵÀý¼ÓÔØºóÉú³ÉµÄClassʵÀýclazz1ºÍclazz2£¬×îºó½«ÕâÁ½¸öClassʵÀý·Ö±ðÉú³É¾ßÌåµÄʵÀý¶ÔÏóobj1ºÍobj2£¬ÔÙͨ¹ý·´Éäµ÷ÓÃclazz1ÖеÄsetNetClassLoaderSimple·½·¨¡£
3£©¡¢²é¿´²âÊÔ½á¹û

½áÂÛ£º´Ó½á¹ûÖпÉÒÔ¿´³ö£¬ËäÈ»ÊÇͬһ·Ýclass×Ö½ÚÂëÎļþ£¬µ«ÊÇÓÉÓÚ±»Á½¸ö²»Í¬µÄClassLoaderʵÀýËù¼ÓÔØ£¬ËùÒÔJVMÈÏΪËüÃǾÍÊÇÁ½¸ö²»Í¬µÄÀà¡£
4¡¢ClassLoaderµÄÌåϵ¼Ü¹¹£º

ÑéÖ¤ClassLoader¼ÓÔØÀàµÄÔÀí£º
²âÊÔ1£º´òÓ¡ClassLoaderÀàµÄ²ã´Î½á¹¹£¬Çë¿´ÏÂÃæÕâ¶Î´úÂ룺
ClassLoader loader =
ClassLoaderTest.class.getClassLoader();
//»ñµÃ¼ÓÔØClassLoaderTest.classÕâ¸öÀàµÄÀà¼ÓÔØÆ÷
while(loader != null) {
System.out.println(loader);
loader = loader.getParent(); //»ñµÃ¸¸Àà¼ÓÔØÆ÷µÄÒýÓÃ
}
System.out.println(loader); |
´òÓ¡½á¹û£º

µÚÒ»Ðнá¹û˵Ã÷£ºClassLoaderTestµÄÀà¼ÓÔØÆ÷ÊÇAppClassLoader¡£
µÚ¶þÐнá¹û˵Ã÷£ºAppClassLoaderµÄÀà¼ÓÆ÷ÊÇExtClassLoader£¬¼´parent=ExtClassLoader¡£
µÚÈýÐнá¹û˵Ã÷£ºExtClassLoaderµÄÀà¼ÓÆ÷ÊÇBootstrap ClassLoader£¬ÒòΪBootstrap
ClassLoader²»ÊÇÒ»¸öÆÕͨµÄJavaÀ࣬ËùÒÔExtClassLoaderµÄparent=null£¬ËùÒÔµÚÈýÐеĴòÓ¡½á¹ûΪnull¾ÍÊÇÕâ¸öÔÒò¡£
²âÊÔ2£º½«ClassLoaderTest.class´ò°ü³ÉClassLoaderTest.jar£¬·Åµ½Extension
ClassLoaderµÄ¼ÓÔØÄ¿Â¼Ï£¨JAVA_HOME/jre/lib/ext£©£¬È»ºóÖØÐÂÔËÐÐÕâ¸ö³ÌÐò£¬µÃµ½µÄ½á¹û»áÊÇʲôÑùÄØ£¿

´òÓ¡½á¹û£º

´òÓ¡½á¹û·ÖÎö£º
ΪʲôµÚÒ»ÐеĽá¹ûÊÇExtClassLoaderÄØ£¿
ÒòΪClassLoaderµÄίÍÐÄ£ÐÍ»úÖÆ£¬µ±ÎÒÃÇÒªÓÃClassLoaderTest.classÕâ¸öÀàµÄʱºò£¬AppClassLoaderÔÚÊÔͼ¼ÓÔØÖ®Ç°£¬ÏÈίÍиøBootstrcp
ClassLoader£¬Bootstracp ClassLoader·¢ÏÖ×Ô¼ºÃ»ÕÒµ½£¬Ëü¾Í¸æËßExtClassLoader£¬Ðֵܣ¬ÎÒÕâÀïûÓÐÕâ¸öÀ࣬ÄãÈ¥¼ÓÔØ¿´¿´£¬È»ºóExtension
ClassLoaderÄÃ×ÅÕâ¸öÀàÈ¥ËüÖ¸¶¨µÄÀà·¾¶£¨JAVA_HOME/jre/lib/ext£©ÊÔͼ¼ÓÔØ£¬°¦£¬Ëü·¢ÏÖÔÚClassLoaderTest.jarÕâÑùÒ»¸öÎļþÖаüº¬ClassLoaderTest.classÕâÑùµÄÒ»¸öÎļþ£¬È»ºóËü°ÑÕÒµ½µÄÕâ¸öÀà¼ÓÔØµ½ÄÚ´æµ±ÖУ¬²¢Éú³ÉÕâ¸öÀàµÄClassʵÀý¶ÔÏó£¬×îºó°ÑÕâ¸öʵÀý·µ»Ø¡£ËùÒÔClassLoaderTest.classµÄÀà¼ÓÔØÆ÷ÊÇExtClassLoader¡£
µÚ¶þÐеĽá¹ûΪnull£¬ÊÇÒòΪExtClassLoaderµÄ¸¸Àà¼ÓÔØÆ÷ÊÇBootstrap ClassLoader¡£
²âÊÔ3£ºÓÃBootstrcp ClassLoaderÀ´¼ÓÔØClassLoaderTest.class£¬ÓÐÁ½ÖÖ·½Ê½£º
1¡¢ÔÚjvmÖÐÌí¼Ó-Xbootclasspath²ÎÊý£¬Ö¸¶¨Bootstrcp ClassLoader¼ÓÔØÀàµÄ·¾¶£¬²¢×·¼ÓÎÒÃÇ×ÔÒѵÄjar£¨ClassTestLoader.jar£©
2¡¢½«classÎļþ·Åµ½JAVA_HOME/jre/classes/Ŀ¼Ï£¨ÉÏÃæÓÐÌáµ½£©
·½Ê½1£º£¨ÎÒÓõÄÊÇEclipse¿ª·¢¹¤¾ß£¬ÓÃÃüÁîÐÐÊÇÔÚjavaÃüÁîºóÃæÌí¼Ó-Xbootclasspath²ÎÊý£©
´ò¿ªRunÅäÖöԻ°¿ò£º

ÅäÖúÃÈçͼÖÐËùÊöµÄ²ÎÊýºó£¬ÖØÐÂÔËÐгÌÐò£¬²úµÄ½á¹ûÈçÏÂËùʾ£º£¨Àà¼ÓÔØµÄ¹ý³Ì£¬Ö»ÕªÏÂÁËÒ»²¿·Ý£©
´òÓ¡½á¹û£º
[Loaded java.io.FileReader from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar] [Loaded sun.nio.cs.StreamDecoder from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar] [Loaded java.util.ArrayList from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar] [Loaded java.lang.reflect.Array from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util.Locale from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.ConcurrentMap from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.ConcurrentHashMap
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.Lock from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.ReentrantLock
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.ConcurrentHashMap$Segment
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.AbstractOwnableSynchronizer
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.AbstractQueuedSynchronizer
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.ReentrantLock$Sync
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.ReentrantLock$NonfairSync
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.locks.AbstractQueuedSynchronizer$Node
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util .concurrent.ConcurrentHashMap$HashEntry
from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.lang .CharacterDataLatin1 from C:\Program
Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.io. ObjectStreamClass from C:\Program
Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded sun.net. www.ParseUtil from C:\Program
Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util.BitSet from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.net.Parts from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar] [Loaded java.net.URLStreamHandler from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded sun.net.www.protocol.file.Handler from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.util.HashSet from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded sun.net.www.protocol.jar.Handler from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded sun.misc.Launcher$AppClassLoader from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded sun.misc.Launcher$AppClassLoader$1 from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.lang .SystemClassLoaderAction from
C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Path C:\Program Files\Java\jdk1.6.0_22\jre\classes]
[Loaded classloader. ClassLoaderTest from C:\Program
Files\Java\jdk1.6.0_22\jre\classes]
null //ÕâÊÇ´òÓ¡µÄ½á¹û C:\Program Files\Java\jdk1.6.0_22\jre\lib\resources.jar; C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar;
C:\Program Files\Java\jdk1.6.0_22\jre\lib\sunrsasign.jar;
C:\Program Files\Java\jdk1.6.0_22\jre\lib\jsse.jar;
C:\Program Files\Java\jdk1.6.0_22\jre\lib\jce.jar;
C:\Program Files\Java\jdk1.6.0_22\jre\lib\charsets.jar;
C:\Program Files\Java\jdk1.6.0_22\jre\classes;
c:\ClassLoaderTest.jar
//ÕâÒ»¶ÎÊÇSystem.out.println (System.getProperty("sun.boot.class.path"));
´òÓ¡³öÀ´µÄ¡£Õâ¸ö·¾¶¾ÍÊÇBootstrcp ClassLoaderĬÈÏËÑË÷ÀàµÄ·¾¶
[Loaded java.lang.Shutdown from C:\Program Files\Java\jdk1.6.0_22\jre\lib\rt.jar]
[Loaded java.lang.Shutdown$Lock from C:\Program
Files\Java\jdk1.6.0_22\jre\lib\rt.jar] |
·½Ê½2£º½«ClassLoaderTest.jar½âѹºó£¬·Åµ½JAVA_HOME/jre/classesĿ¼Ï£¬ÈçÏÂͼËùʾ£º
Ìáʾ£ºjreĿ¼ÏÂĬÈÏûÓÐclassesĿ¼£¬ÐèÒª×Ô¼ºÊÖ¶¯´´½¨Ò»¸ö

´òÓ¡½á¹û£º

´Ó½á¹ûÖпÉÒÔ¿´³ö£¬Á½ÖÖ·½Ê½¶¼ÊµÏÖÁ˽«ClassLoaderTest.classÓÉBootstrcp
ClassLoader¼ÓÔØ³É¹¦ÁË¡£
ËÄ¡¢¶¨Òå×ÔÒѵÄClassLoader
¼ÈÈ»JVMÒѾÌṩÁËĬÈϵÄÀà¼ÓÔØÆ÷£¬ÎªÊ²Ã´»¹Òª¶¨Òå×ÔÒѵÄÀà¼ÓÔØÆ÷ÄØ£¿
ÒòΪJavaÖÐÌṩµÄĬÈÏClassLoader£¬Ö»¼ÓÔØÖ¸¶¨Ä¿Â¼ÏµÄjarºÍclass£¬Èç¹ûÎÒÃÇÏë¼ÓÔØÆäËüλÖõÄÀà»òjarʱ£¬±ÈÈ磺ÎÒÒª¼ÓÔØÍøÂçÉϵÄÒ»¸öclassÎļþ£¬Í¨¹ý¶¯Ì¬¼ÓÔØµ½ÄÚ´æÖ®ºó£¬Òªµ÷ÓÃÕâ¸öÀàÖеķ½·¨ÊµÏÖÎÒµÄÒµÎñÂß¼¡£ÔÚÕâÑùµÄÇé¿öÏ£¬Ä¬ÈϵÄClassLoader¾Í²»ÄÜÂú×ãÎÒÃǵÄÐèÇóÁË£¬ËùÒÔÐèÒª¶¨Òå×Ô¼ºµÄClassLoader¡£
¶¨Òå×ÔÒѵÄÀà¼ÓÔØÆ÷·ÖΪÁ½²½£º
1¡¢¼Ì³Ðjava.lang.ClassLoader
2¡¢ÖØÐ´¸¸ÀàµÄfindClass·½·¨
¶ÁÕß¿ÉÄÜÔÚÕâÀïÓÐÒÉÎÊ£¬¸¸ÀàÓÐÄÇô¶à·½·¨£¬ÎªÊ²Ã´Æ«Æ«Ö»ÖØÐ´findClass·½·¨£¿
ÒòΪJDKÒѾÔÚloadClass·½·¨ÖаïÎÒÃÇʵÏÖÁËClassLoaderËÑË÷ÀàµÄËã·¨£¬µ±ÔÚloadClass·½·¨ÖÐËÑË÷²»µ½Ààʱ£¬loadClass·½·¨¾Í»áµ÷ÓÃfindClass·½·¨À´ËÑË÷À࣬ËùÒÔÎÒÃÇÖ»ÐèÖØÐ´¸Ã·½·¨¼´¿É¡£ÈçûÓÐÌØÊâµÄÒªÇó£¬Ò»°ã²»½¨ÒéÖØÐ´loadClassËÑË÷ÀàµÄËã·¨¡£ÏÂͼÊÇAPIÖÐClassLoaderµÄloadClass·½·¨£º

ʾÀý£º×Ô¶¨ÒåÒ»¸öNetworkClassLoader£¬ÓÃÓÚ¼ÓÔØÍøÂçÉϵÄclassÎļþ
package classloader;
import java.io.ByteArrayOutputStream;
import java.io.InputStream;
import java.net.URL;
/**
* ¼ÓÔØÍøÂçclassµÄClassLoader
*/
public class NetworkClassLoader extends ClassLoader
{
private String rootUrl;
public NetworkClassLoader(String rootUrl)
{
this.rootUrl = rootUrl;
}
@Override
protected Class<?> findClass(String name)
throws ClassNotFoundException {
Class clazz = null;//this.findLoadedClass(name);
// ¸¸ÀàÒѼÓÔØ
//if (clazz == null) { //¼ì²é¸ÃÀàÊÇ·ñÒѱ»¼ÓÔØ¹ý
byte[] classData = getClassData(name); //¸ù¾ÝÀàµÄ¶þ½øÖÆÃû³Æ,»ñµÃ¸ÃclassÎļþµÄ×Ö½ÚÂëÊý×é
if (classData == null) {
throw new ClassNotFoundException();
}
clazz = defineClass(name, classData, 0, classData.length);
//½«classµÄ×Ö½ÚÂëÊý×éת»»³ÉClassÀàµÄʵÀý
//}
return clazz;
}
private byte[] getClassData(String name) {
InputStream is = null;
try {
String path = classNameToPath(name);
URL url = new URL(path);
byte[] buff = new byte[1024*4];
int len = -1;
is = url.openStream();
ByteArrayOutputStream baos = new ByteArrayOutputStream();
while((len = is.read(buff)) != -1) {
baos.write(buff,0,len);
}
return baos.toByteArray();
} catch (Exception e) {
e.printStackTrace();
} finally {
if (is != null) {
try {
is.close();
} catch(IOException e) {
e.printStackTrace();
}
}
}
return null;
}
private String classNameToPath(String name)
{
return rootUrl + "/" + name.replace(".",
"/") + ".class";
}
} |
²âÊÔÀࣺ
package classloader;
public class ClassLoaderTest {
public static void main(String[] args) {
try {
/*ClassLoader loader = ClassLoaderTest.class.getClassLoader();
//»ñµÃClassLoaderTestÕâ¸öÀàµÄÀà¼ÓÔØÆ÷
while(loader != null) {
System.out.println(loader);
loader = loader.getParent(); //»ñµÃ¸¸¼ÓÔØÆ÷µÄÒýÓÃ
}
System.out.println(loader);*/
String rootUrl = "http://localhost:8080/httpweb/classes";
NetworkClassLoader networkClassLoader = new
NetworkClassLoader(rootUrl);
String classname = "org.classloader.simple.NetClassLoaderTest";
Class clazz = networkClassLoader.loadClass(classname);
System.out.println(clazz.getClassLoader());
} catch (Exception e) {
e.printStackTrace();
}
}
} |
´òÓ¡½á¹û£º

ÏÂͼÊÇÎÒ»úÆ÷ÉÏweb·þÎñÆ÷µÄĿ¼½á¹¹£º

Ŀǰ³£ÓÃweb·þÎñÆ÷Öж¼¶¨ÒåÁË×Ô¼ºµÄÀà¼ÓÔØÆ÷£¬ÓÃÓÚ¼ÓÔØwebÓ¦ÓÃÖ¸¶¨Ä¿Â¼ÏµÄÀà¿â£¨jar»òclass£©£¬È磺Weblogic¡¢Jboss¡¢tomcatµÈ£¬ÏÂÃæÎÒÒÔTomcatΪÀý£¬Õ¹Ê¾¸ÃwebÈÝÆ÷¶¼¶¨ÒåÁËÄÄЩ¸öÀà¼ÓÔØÆ÷£º
1¡¢Ð½¨Ò»¸öweb¹¤³Ìhttpweb
2¡¢Ð½¨Ò»¸öClassLoaderServletTest£¬ÓÃÓÚ´òÓ¡webÈÝÆ÷ÖеÄClassLoader²ã´Î½á¹¹
import java.io.IOException; import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ClassLoaderServletTest extends
HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
response.setContentType("text/html");
PrintWriter out = response.getWriter();
ClassLoader loader = this.getClass().getClassLoader();
while(loader != null) {
out.write(loader.getClass().getName()+"<br/>");
loader = loader.getParent();
}
out.write(String.valueOf(loader));
out.flush();
out.close();
}
public void doPost(HttpServletRequest request,
HttpServletResponse response)
throws ServletException, IOException {
this.doGet(request, response);
}
} |
3¡¢ÅäÖÃServlet£¬²¢Æô¶¯·þÎñ
4¡¢·ÃÎÊServlet£¬»ñµÃÏÔʾ½á¹û

|