Android Xposed Hook PackageManagerService Didn't find class "com.android.server.pm.PackageManagerService"

Question

Suppressed: java.lang.ClassNotFoundException: Didn't find class "com.android.server.pm.PackageManagerService"

public class HookAPM_6 implements IXposedHookLoadPackage {

@Override
public void handleLoadPackage(XC_LoadPackage.LoadPackageParam lpparam) throws Throwable {

    Class<?> packageManagerService = XposedHelpers.findClass("com.android.server.pm.PackageManagerService",
            lpparam.classLoader);

    XposedHelpers.findAndHookMethod(packageManagerService, "installPackageLI",
            "com.android.server.pm.PackageManagerService.InstallArgs",
            "com.android.server.pm.PackageManagerService.PackageInstalledInfo",
            new XC_MethodHook() {
                @Override
                protected void beforeHookedMethod(MethodHookParam param) throws Throwable {
                    super.beforeHookedMethod(param);
                }
            });

please~

When I use the above code to hook the system service (packagemanagerservice), it will report an error. The specific error is: "caused by: java.lang.classnotfoundexception: com.android.server.pm. PackageManagerService"

what's wrong please? and How should I write it？

The device is running Android 6.0.1.