//查詢所有被啟動(dòng)類加載器加載的類
URL[] urls = sun.misc.Launcher.getBootstrapClassPath().getURLs();
for (URL url : urls) {
    System.out.println(url);
}

//查詢到的結(jié)果
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/resources.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/rt.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/sunrsasign.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/jsse.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/jce.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/charsets.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/jfr.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/classes

URL[] urls = ((URLClassLoader) ClassLoader.getSystemClassLoader().getParent()).getURLs();
for (URL url : urls) {
    System.out.println(url);
}

file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/access-bridge-64.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/cldrdata.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/dnsns.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/dns_sd.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/jaccess.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/jfxrt.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/localedata.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/nashorn.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/sunec.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/sunjce_provider.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/sunmscapi.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/sunpkcs11.jar
file:/C:/Program%20Files/Java/jre1.8.0_131/lib/ext/zipfs.jar

URL[] urls = ((URLClassLoader) ClassLoader.getSystemClassLoader()).getURLs();
for (URL url : urls) {
    System.out.println(url);
}

file:/{項(xiàng)目工程目錄}/bin/

protected Class<?> loadClass(String name, boolean resolve)
    throws ClassNotFoundException
{
    synchronized (getClassLoadingLock(name)) {
        // 首先查找該類是否已經(jīng)被該類加載器加載過了
        Class<?> c = findLoadedClass(name);
        //如果沒有被加載過
        if (c == null) {
            long t0 = System.nanoTime();
            try {
                //看是否被它的上級(jí)加載器加載過了 Extension的上級(jí)是Bootstarp，但它顯示為null
                if (parent != null) {
                    c = parent.loadClass(name, false);
                } else {
                    //看是否被啟動(dòng)類加載器加載過
                    c = findBootstrapClassOrNull(name);
                }
            } catch (ClassNotFoundException e) {
                // ClassNotFoundException thrown if class not found
                // from the non-null parent class loader
                //捕獲異常，但不做任何處理
            }
            if (c == null) {
                //如果還是沒有找到，先讓拓展類加載器調(diào)用findClass方法去找到該類，如果還是沒找到，就拋出異常
                //然后讓應(yīng)用類加載器去找classpath下找該類
                long t1 = System.nanoTime();
                c = findClass(name);
                // 記錄時(shí)間
                sun.misc.PerfCounter.getParentDelegationTime().addTime(t1 - t0);
                sun.misc.PerfCounter.getFindClassTime().addElapsedTimeFrom(t1);
                sun.misc.PerfCounter.getFindClasses().increment();
            }
        }
        if (resolve) {
            resolveClass(c);
        }
        return c;
    }
}

protected Class<?> findClass(final String name) throws ClassNotFoundException {
    // 1、安全檢查
    // 2、根據(jù)絕對(duì)路徑把硬盤上class文件讀入內(nèi)存
    byte[] raw = getBytes(name); 
    // 3、將二進(jìn)制數(shù)據(jù)轉(zhuǎn)換成class對(duì)象
    return defineClass(raw);
}