我对谷歌文档有疑问。我想使用 OAuth 2.0 检索您的所有文件。问题是，一旦你这样做了，尝试下载文件时的授权会给我这个错误：
Exception in thread "main" java.lang.NullPointerException
at GoogleBlack.readUrl(GoogleBlack.java:95)
at GoogleBlack.getDocument(GoogleBlack.java:87)
at GoogleBlack.go(GoogleBlack.java:187)
at GoogleBlack.main(GoogleBlack.java:222)
这是我使用的代码
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.net.URL;
import java.util.Arrays;
import java.util.List;
import com.google.api.client.auth.oauth2.Credential;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeRequestUrl;
import com.google.api.client.googleapis.auth.oauth2.GoogleAuthorizationCodeTokenRequest;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.googleapis.auth.oauth2.GoogleTokenResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.json.jackson.JacksonFactory;
import com.google.gdata.client.GoogleService;
import com.google.gdata.client.GoogleAuthTokenFactory.UserToken;
import com.google.gdata.client.docs.DocsService;
import com.google.gdata.data.MediaContent;
import com.google.gdata.data.docs.DocumentListEntry;
import com.google.gdata.data.docs.DocumentListFeed;
import com.google.gdata.data.media.MediaSource;
import com.google.gdata.util.ServiceException;
public class GoogleBlack {
private static final String APPLICATION_NAME = "Homework";
public DocsService service;
public GoogleService spreadsheetsService;
static String CLIENT_ID = "***********";
static String CLIENT_SECRET = "**************";
static String REDIRECT_URI = "urn:ietf:wg:oauth:2.0:oob";
static List<String> SCOPES = Arrays.asList("https://docs.google.com/feeds");
public void getSpreadSheet(String id, String i, String ids, String type) throws Exception {
UserToken docsToken = (UserToken) service.getAuthTokenFactory()
.getAuthToken();
UserToken spreadsheetsToken = (UserToken) spreadsheetsService
.getAuthTokenFactory().getAuthToken();
service.setUserToken(spreadsheetsToken.getValue());
URL url = null;
if(type.equals("doc"))
{
url = new URL("https://docs.google.com/feeds/download/documents/Export?id="+ ids);
}
else
{
url = new URL("https://docs.google.com/feeds/download/spreadsheets/Export?key="+ ids +"&exportFormat="+ type + "&gid=0");
i += ".xls";
}
System.out.println("Spred = " + url.toString());
readUrl1(url.toString(), i, type);
service.setUserToken(docsToken.getValue());
}
public void readUrl1(String url, String i, String type) throws IOException, ServiceException
{
MediaContent mc = new MediaContent();
mc.setUri(url);
MediaSource ms = service.getMedia(mc);
System.out.println("Name: "+i);
BufferedInputStream bin = new BufferedInputStream(ms.getInputStream());
OutputStream out = new FileOutputStream(i);
BufferedOutputStream bout = new BufferedOutputStream(out);
while (true) {
int datum = bin.read();
if (datum == -1)
break;
bout.write(datum);
}
bout.flush();
}
public void getDocument(String id, String i) throws Exception {
URL url = new URL(id);
readUrl(url,i);
}
public void readUrl(URL url, String i) throws Exception {
MediaContent mc = new MediaContent();
mc.setUri(url.toString());
System.out.println("Url "+ url.toString());
System.out.println("MC: " + mc.toString());
MediaSource ms = service.getMedia(mc);
System.out.println("Name: "+i);
BufferedInputStream bin = new BufferedInputStream(ms.getInputStream());
OutputStream out = new FileOutputStream(i);
BufferedOutputStream bout = new BufferedOutputStream(out);
while (true) {
int datum = bin.read();
if (datum == -1)
break;
bout.write(datum);
}
bout.flush();
// FileOutputStream fout = null;
// fout = new FileOutputStream(i);
// fout.write(cbuf.);
// fout.close();
}
static Credential getCredentials() {
HttpTransport transport = new NetHttpTransport();
JacksonFactory jsonFactory = new JacksonFactory();
// Step 1: Authorize -->
String authorizationUrl =
new GoogleAuthorizationCodeRequestUrl(CLIENT_ID, REDIRECT_URI, SCOPES).build();
// Point or redirect your user to the authorizationUrl.
System.out.println("Go to the following link in your browser:");
System.out.println(authorizationUrl);
// Read the authorization code from the standard input stream.
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What is the authorization code?");
String code = null;
try {
code = in.readLine();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// End of Step 1 <--
// Step 2: Exchange -->
GoogleTokenResponse response = null;
try {
response = new GoogleAuthorizationCodeTokenRequest(transport, jsonFactory, CLIENT_ID, CLIENT_SECRET,
code, REDIRECT_URI).execute();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
// End of Step 2 <--
// Build a new GoogleCredential instance and return it.
return new GoogleCredential.Builder().setClientSecrets(CLIENT_ID, CLIENT_SECRET)
.setJsonFactory(jsonFactory).setTransport(transport).build()
.setAccessToken(response.getAccessToken()).setRefreshToken(response.getRefreshToken());
}
public void go() throws Exception {
DocsService service = new DocsService(APPLICATION_NAME);
service.setOAuth2Credentials(getCredentials());
URL feedUrl = new URL("https://docs.google.com/feeds/default/private/full/");
DocumentListFeed feed = service.getFeed(feedUrl, DocumentListFeed.class);
System.out.println("Feed " + feed.getEntries().size());
for(int i = 0; i < feed.getEntries().size(); i++)
{
DocumentListEntry entry = feed.getEntries().get(i);
if(entry.getType().equals("file"))
{
MediaContent mc1 = (MediaContent) entry.getContent();
String UrlForDownload = mc1.getUri();
System.out.println("Type is: " + entry.getType());
System.out.println("File Name is: " + entry.getTitle().getPlainText());
System.out.println("URL "+ UrlForDownload);
getDocument(UrlForDownload, entry.getFilename());
}
else
{
MediaContent mc1 = (MediaContent) entry.getContent();
String UrlForDownload = mc1.getUri();
System.out.println("URL "+ UrlForDownload);
System.out.println("Type is: " + entry.getType());
System.out.println("File Name is: " + entry.getTitle().getPlainText());
if(entry.getTitle().getPlainText().equals("Web Design 2011/2012 - Материали"))
{
continue;
}
if(entry.getType().equals("spreadsheet"))
{
String name = entry.getTitle().getPlainText().replaceAll(" ", "");
System.out.println("name: " + name);
getSpreadSheet(UrlForDownload, name, entry.getDocId(),"xls");
}
else
{
String name = entry.getTitle().getPlainText().replaceAll(" ", "");
System.out.println("name: " + name);
getSpreadSheet(UrlForDownload, name, entry.getDocId(),"doc");
}
}
}
}
public static void main(String[] args) throws Exception {
new GoogleBlack().go();
}
}
第 95 行 - MediaSource ms = service.getMedia(mc);
87 行 - readUrl(url,i);
第187行-getDocument（UrlForDownload，entry.getFilename（））；
222 行 - 新的 GoogleBlack().go();
如果我没有得到很好的解释，我深表歉意！！！