/** Determine JDK level of an applet. */
private void findAppletJDKLevel(Applet applet) {
// To determine the JDK level of an applet, the
// most reliable way is to check the major version
// of the applet class file.
// synchronized on applet class object, so calling from
// different instances of the same applet will be
// serialized.
Class<?> appletClass = applet.getClass();
synchronized (appletClass) {
// Determine if the JDK level of an applet has been
// checked before.
Boolean jdk11Target = loader.isJDK11Target(appletClass);
Boolean jdk12Target = loader.isJDK12Target(appletClass);
// if applet JDK level has been checked before, retrieve
// value and return.
if (jdk11Target != null || jdk12Target != null) {
jdk11Applet = (jdk11Target == null) ? false : jdk11Target.booleanValue();
jdk12Applet = (jdk12Target == null) ? false : jdk12Target.booleanValue();
return;
}
String name = appletClass.getName();
// first convert any '.' to '/'
name = name.replace('.', '/');
// append .class
final String resourceName = name + ".class";
byte[] classHeader = new byte[8];
try (InputStream is =
AccessController.doPrivileged(
(PrivilegedAction<InputStream>) () -> loader.getResourceAsStream(resourceName))) {
// Read the first 8 bytes of the class file
int byteRead = is.read(classHeader, 0, 8);
// return if the header is not read in entirely
// for some reasons.
if (byteRead != 8) return;
} catch (IOException e) {
return;
}
// Check major version in class file header
int major_version = readShort(classHeader, 6);
// Major version in class file is as follows:
// 45 - JDK 1.1
// 46 - JDK 1.2
// 47 - JDK 1.3
// 48 - JDK 1.4
// 49 - JDK 1.5
if (major_version < 46) jdk11Applet = true;
else if (major_version == 46) jdk12Applet = true;
// Store applet JDK level in AppContext for later lookup,
// e.g. page switch.
loader.setJDK11Target(appletClass, jdk11Applet);
loader.setJDK12Target(appletClass, jdk12Applet);
}
}
