WIkipedia rest api pdf下载NullPointerException

Question

我正在尝试使用新的Wikipedia rest api {https://en.wikipedia.org/api/rest_v1/#!/Page_content/generatePDF）get为Wikipedia文章创建pdf文件。

我正在通过此链接（http://www.benchresources.net/resteasy-jax-rs-web-service-for-uploadingdownloading-pdf-file-java-client/）使用类TestDownloadFileService.java。这是我的课程：

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import org.glassfish.jersey.client.*;
import javax.ws.rs.client.Client;
import javax.ws.rs.client.ClientBuilder;
import javax.ws.rs.client.Invocation.Builder;
import javax.ws.rs.client.WebTarget;
import javax.ws.rs.core.Response;


    public class TestDownloadFileService {

        public static final String DOWNLOAD_FILE_LOCATION = "/home/Downloads";

        public static void main(String []args) throws IOException {

            String httpURL = "https://en.wikipedia.org/api/rest_v1/page/pdf/Forest";
            String responseString =  testDownloadService(httpURL);
            System.out.println("responseString : " + responseString);
        }

        /**
         * using Client, WebTarget from core JAX-RS classes javax.ws.rs.client
         * @param url
         */
        public static String testDownloadService(String httpURL) throws IOException {

            // local variables
            Client client = null;
            WebTarget webTarget = null;
            Builder builder = null;
            Response response = null;
            InputStream inputStream = null;
            OutputStream outputStream = null;
            int responseCode;
            String responseMessageFromServer = null;
            String responseString = null;
            String qualifiedDownloadFilePath = null;

            try {
                // invoke service after setting necessary parameters
                client = ClientBuilder.newClient();
                webTarget = client.target(httpURL);
                client.property("accept", "application/pdf");
                builder = webTarget.request();
                response = builder.get();

                // get response code
                responseCode = response.getStatus();
                System.out.println("Response code: " + responseCode);

                if (response.getStatus() != 200) {
                    throw new RuntimeException("Failed with HTTP error code : " + responseCode);
                }

                // get response message
                responseMessageFromServer = response.getStatusInfo().getReasonPhrase();
                System.out.println("ResponseMessageFromServer: " + responseMessageFromServer);

                // read response string
                inputStream = response.readEntity(InputStream.class);
                qualifiedDownloadFilePath = DOWNLOAD_FILE_LOCATION + "MyPdfFile.pdf";
                outputStream = new FileOutputStream(qualifiedDownloadFilePath);
                byte[] buffer = new byte[1024];
                int bytesRead;
                while ((bytesRead = inputStream.read(buffer)) != -1) {
                    outputStream.write(buffer, 0, bytesRead);
                }

                // set download SUCCES message to return
                responseString = "downloaded successfully at " + qualifiedDownloadFilePath;
            }
            catch(Exception ex) {
                ex.printStackTrace();
            }
            finally{
                // release resources, if any
               outputStream.close();
              client.close();
            }
            return responseString;
        }
    }

但是我在第87行和第26行分别得到了NullPointerException：

client.close();
String responseString =  testDownloadService(httpURL);

在此先感谢您指出原因和解决方案。