问题出现的原因是Android 9对网络请求做了一些限制，需要通过在AndroidManifest.xml文件中配置请求权限来解决。

解决方法： 在AndroidManifest.xml文件中添加以下代码：

示例代码：

public class MainActivity extends AppCompatActivity {

    private static final int REQUEST_CODE_SIGN_IN = 1;
    private GoogleSignInClient mGoogleSignInClient;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // Configure Google Sign In
        GoogleSignInOptions gso = new GoogleSignInOptions.Builder(GoogleSignInOptions.DEFAULT_SIGN_IN)
                .requestEmail()
                .build();
        mGoogleSignInClient = GoogleSignIn.getClient(this, gso);

        SignInButton signInButton = findViewById(R.id.sign_in_button);
        signInButton.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Intent signInIntent = mGoogleSignInClient.getSignInIntent();
                startActivityForResult(signInIntent, REQUEST_CODE_SIGN_IN);
            }
        });
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, @Nullable Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        // Result returned from launching the Intent from GoogleSignInApi.getSignInIntent(...);
        if (requestCode == REQUEST_CODE_SIGN_IN) {
            Task task = GoogleSignIn.getSignedInAccountFromIntent(data);
            handleSignInResult(task);
        }
    }

    private void handleSignInResult(Task completedTask) {
        try {
            GoogleSignInAccount account = completedTask.getResult(ApiException.class);

            // Signed in successfully, show authenticated UI.
            Toast.makeText(this, "Signed in as " + account.getDisplayName(), Toast.LENGTH_SHORT).show();

        } catch (ApiException e) {
            // The ApiException status code indicates the detailed failure reason.
            // Please refer to the GoogleSignInStatusCodes class reference for more information.
            Log.w("TAG", "signInResult:failed code=" + e.getStatusCode());
            Toast.makeText(this, "SignIn Failed", Toast.LENGTH_SHORT).show();
        }
    }
}