引子
事件描述
开发环境：Mac， dea，Spring boot 1.5.3.RELEASE
在开发微信小程序客服消息的时候，需要针对context为1的内容回复一张图片。
因为，微信小程序相关的配置都是写在Common模板下的，所以就把图片放在Common模块下的resource中。
IDEA中，使用以下代码都能拿到图片对象。
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| InputStream is = ClassLoader.getSystemResourceAsStream("qrcode_for_gh_ac1de8498046_258.jpg");
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| InputStream is = WxMaServiceConfiguration.class.getResourceAsStream("/qrcode_for_gh_ac1de8498046_258.jpg");
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当项目部署到服务器上的tomcat的时候，以上两个方法就都找不到图片对象了。
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| -webroot
-WEB-INF
-classes
-application.properties
......
-lib
-xxx-common-1.0.0-SNAPSHOT.jar(jarz中包含了图片)
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为什么开发环境可以加载，部署到服务器上就加载不了了呢？
分析
ClassLoader.getSystemResourceAsStream
java.lang.ClassLoader
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| public abstract class ClassLoader {
public static InputStream getSystemResourceAsStream(String name) {
URL url = getSystemResource(name);
try {
return url != null ? url.openStream() : null;
} catch (IOException e) {
return null;
}
}
public static URL getSystemResource(String name) {
ClassLoader system = getSystemClassLoader();
if (system == null) {
return getBootstrapResource(name);
}
return system.getResource(name);
}
@CallerSensitive
public static ClassLoader getSystemClassLoader() {
initSystemClassLoader();
if (scl == null) {
return null;
}
SecurityManager sm = System.getSecurityManager();
if (sm != null) {
checkClassLoaderPermission(scl, Reflection.getCallerClass());
}
return scl;
}
private static synchronized void initSystemClassLoader() {
if (!sclSet) {
if (scl != null)
throw new IllegalStateException("recursive invocation");
sun.misc.Launcher l = sun.misc.Launcher.getLauncher();
if (l != null) {
Throwable oops = null;
scl = l.getClassLoader();
try {
scl = AccessController.doPrivileged(
new SystemClassLoaderAction(scl));
} catch (PrivilegedActionException pae) {
oops = pae.getCause();
if (oops instanceof InvocationTargetException) {
oops = oops.getCause();
}
}
if (oops != null) {
if (oops instanceof Error) {
throw (Error) oops;
} else {
throw new Error(oops);
}
}
}
sclSet = true;
}
}
private static URL getBootstrapResource(String name) {
URLClassPath ucp = getBootstrapClassPath();
Resource res = ucp.getResource(name);
return res != null ? res.getURL() : null;
}
static URLClassPath getBootstrapClassPath() {
return sun.misc.Launcher.getBootstrapClassPath();
}
......
}
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sun.misc.Launcher
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public class Launcher {
private static URLStreamHandlerFactory factory = new Launcher.Factory();
private static Launcher launcher = new Launcher();
private static String bootClassPath = System.getProperty("sun.boot.class.path");
private ClassLoader loader;
......
public Launcher() {
Launcher.ExtClassLoader var1;
try {
var1 = Launcher.ExtClassLoader.getExtClassLoader();
} catch (IOException var10) {
throw new InternalError("Could not create extension class loader", var10);
}
try {
this.loader = Launcher.AppClassLoader.getAppClassLoader(var1);
} catch (IOException var9) {
throw new InternalError("Could not create application class loader", var9);
}
Thread.currentThread().setContextClassLoader(this.loader);
......
}
public static URLClassPath getBootstrapClassPath() {
return Launcher.BootClassPathHolder.bcp;
}
......
private static class BootClassPathHolder {
static final URLClassPath bcp;
private BootClassPathHolder() {}
static {
URL[] var0;
if (Launcher.bootClassPath != null) {
var0 = (URL[])AccessController.doPrivileged(new PrivilegedAction<URL[]>() {
public URL[] run() {
File[] var1 = Launcher.getClassPath(Launcher.bootClassPath);
int var2 = var1.length;
HashSet var3 = new HashSet();
for(int var4 = 0; var4 < var2; ++var4) {
File var5 = var1[var4];
if (!var5.isDirectory()) {
var5 = var5.getParentFile();
}
if (var5 != null && var3.add(var5)) {
MetaIndex.registerDirectory(var5);
}
}
return Launcher.pathToURLs(var1);
}
});
} else {
var0 = new URL[0];
}
bcp = new URLClassPath(var0, Launcher.factory, (AccessControlContext)null);
bcp.initLookupCache((ClassLoader)null);
}
}
static class AppClassLoader extends URLClassLoader {
public static ClassLoader getAppClassLoader(final ClassLoader var0) throws IOException {
final String var1 = System.getProperty("java.class.path");
final File[] var2 = var1 == null ? new File[0] : Launcher.getClassPath(var1);
return (ClassLoader)AccessController.doPrivileged(new PrivilegedAction<Launcher.AppClassLoader>() {
public Launcher.AppClassLoader run() {
URL[] var1x = var1 == null ? new URL[0] : Launcher.pathToURLs(var2);
return new Launcher.AppClassLoader(var1x, var0);
}
});
}
......
}
}
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从上面代码可以知道，java.lang.ClassLoader#getSystemClassLoader 获取是 sun.misc.Launcher.AppClassLoader。
java.lang.ClassLoader#getBootstrapResource 方法，返回的是 sun.misc.URLClassPath 对象。这个对象是在rt.jar包中的。
https://blog.csdn.net/briblue/article/details/54973413 详细看下 这里的classloader内容。
XXX.class.getResourceAsStream
WebappClassLoader 可以加载 jar中的资源文件
WebappClassLoader
context:
delegate: false
repositories:
/WEB-INF/classes/
———-> Parent Classloader:
org.apache.catalina.loader.StandardClassLoader@2145b572
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| ClassLoader.getSystemClassLoader().getClass()
class sun.misc.Launcher$AppClassLoader
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原文链接: https://adeng-wc.github.io/2019/05/22/Resource/
版权声明: 转载请注明出处.