如何使用Gmail API检索电子邮件正文内容？

我正在研究Gmail API。假设我有兴趣查看哪个邮件包含字符串“ foobar2000”。

到目前为止，这是我的代码：

Main.java

package manhattan.email.bot;

import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport; import com.google.api.services.gmail.model.Message; import com.google.api.services.gmail.model.MessagePart; import java.io.IOException; import java.io.UnsupportedEncodingException; import java.nio.charset.StandardCharsets; import java.security.GeneralSecurityException; import java.util.List; import java.util.Properties;

import manhattan.email.bot.google.GmailCredentials; import manhattan.email.bot.google.GmailService; import manhattan.email.bot.google.GmailServiceImpl; import org.apache.commons.codec.binary.Base64; import org.apache.commons.codec.binary.StringUtils;

public class Main {

static final String MY_EMAIL = "xxxxx@gmail.com";
static final String MY_CLIENT_ID = "xxxxxapps.googleusercontent.com";    
static final String MY_CLIENT_SECRET = "xxxxx";
static final String MY_ACCESS_TOKEN = "xxxxx";
static final String MY_REFRESH_TOKEN = "xxxxx";

public static void main(String[] args) {
    try {
        GmailService gmailService = new GmailServiceImpl(GoogleNetHttpTransport.newTrustedTransport());
        gmailService.setGmailCredentials(GmailCredentials.builder()
                .userEmail(MY_EMAIL)
                .clientId(MY_CLIENT_ID)
                .clientSecret(MY_CLIENT_SECRET)
                .accessToken(MY_ACCESS_TOKEN)
                .refreshToken(MY_REFRESH_TOKEN)
                .build());

       List<com.google.api.services.gmail.model.Message> messageList = gmailService.listMessagesMatchingQuery(MY_EMAIL,"foobar2000");
       System.out.println("Search result: ");

       for (Message m:messageList){
           System.out.println(m.toPrettyString());
        }

    }
    catch (GeneralSecurityException gse){
        System.err.println(">>> GSE: "+gse.getMessage());
    }
    catch (IOException ioe){
        System.err.println(">>> IOE: "+ioe.getMessage());
    }
}

} GmailCredentials.java

package manhattan.email.bot.google;

import lombok.Builder; import lombok.Data;

@Builder @Data public class GmailCredentials { private final String userEmail; private final String clientId; private final String clientSecret; private final String accessToken; private final String refreshToken; } GmailService.java

package manhattan.email.bot.google;

import com.google.api.services.gmail.model.Message; import java.io.IOException; import java.util.List; import javax.mail.MessagingException;

public interface GmailService {

void setGmailCredentials(GmailCredentials credentials);
boolean sendMessage(String recipientAddress, String subject, String body) throws MessagingException, IOException;
List<Message> listMessagesMatchingQuery(String userId, String query) throws IOException; 

} GmailServiceImpl.java

package manhattan.email.bot.google;

import com.google.api.client.auth.oauth2.Credential; import com.google.api.client.googleapis.auth.oauth2.GoogleCredential; import com.google.api.client.http.HttpTransport; import com.google.api.client.json.JsonFactory; import com.google.api.client.json.jackson2.JacksonFactory; import com.google.api.client.util.Base64; import com.google.api.services.gmail.Gmail; import com.google.api.services.gmail.model.ListMessagesResponse; import com.google.api.services.gmail.model.Message; import java.io.ByteArrayOutputStream; import java.io.IOException; import java.util.ArrayList; import java.util.List; import java.util.Properties; import javax.mail.MessagingException; import javax.mail.Session; import javax.mail.internet.InternetAddress; import javax.mail.internet.MimeMessage;

/** * * @author OCIN */ public class GmailServiceImpl implements GmailService {

private static final String APPLICATION_NAME = "mail-bot";
private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();

private final HttpTransport httpTransport;
private GmailCredentials gmailCredentials;

public GmailServiceImpl(HttpTransport transport){
    this.httpTransport = transport;
}

private Gmail createGmail() {
    Credential credential = authorize();
    return new Gmail.Builder(httpTransport, JSON_FACTORY, credential)
            .setApplicationName(APPLICATION_NAME)
            .build();
}

 private Credential authorize() {
    return new GoogleCredential.Builder()
            .setTransport(httpTransport)
            .setJsonFactory(JSON_FACTORY)
            .setClientSecrets(gmailCredentials.getClientId(), gmailCredentials.getClientSecret())
            .build()
            .setAccessToken(gmailCredentials.getAccessToken())
            .setRefreshToken(gmailCredentials.getRefreshToken());
}

@Override
public void setGmailCredentials(GmailCredentials credentials) {
    this.gmailCredentials = credentials;
}

 private MimeMessage createEmail(String to, String from, String subject, String bodyText) throws MessagingException {
    MimeMessage email = new MimeMessage(Session.getDefaultInstance(new Properties(), null));
    email.setFrom(new InternetAddress(from));
    email.addRecipient(javax.mail.Message.RecipientType.TO, new InternetAddress(to));
    email.setSubject(subject);
    email.setText(bodyText);
    return email;
}

private Message createMessageWithEmail(MimeMessage emailContent) throws MessagingException, IOException {
    ByteArrayOutputStream buffer = new ByteArrayOutputStream();
    emailContent.writeTo(buffer);

    return new Message().setRaw(Base64.encodeBase64URLSafeString(buffer.toByteArray()));
}

@Override
public boolean sendMessage(String recipientAddress, String subject, String body) throws MessagingException, IOException {
    Message message = createMessageWithEmail(
        createEmail(recipientAddress, gmailCredentials.getUserEmail(), subject, body));

    return createGmail().users()
        .messages()
        .send(gmailCredentials.getUserEmail(), message)
        .execute()
        .getLabelIds().contains("SENT");
}

public List<Message> listMessagesMatchingQuery(String userId, String query) throws IOException {
    ListMessagesResponse response = createGmail().users().messages().list(userId).setQ(query).execute();
    List<Message> messages = new ArrayList<Message>();

    while (response.getMessages() != null) {
        messages.addAll(response.getMessages());
        if (response.getNextPageToken() != null) {
            String pageToken = response.getNextPageToken();
            response = createGmail().users().messages().list(userId).setQ(query).setPageToken(pageToken).execute();
        } 
        else {
            break;
        }
    }

   // for (Message message : messages) {
   //     System.out.println(message.toPrettyString());
   // }

    return messages;
}

} 我的代码的输出是：

搜索结果：{“ id”：“ 16d929a8524a6bbd”，“ threadId”：“ 16d929a8524a6bbd”}

的确如此，因为体内只有1个带有“ foobar2000”的邮件。全文如下：

bla bla bla foobar2000你好世界

如何获得？我试过在循环中使用它：

System.out.println(StringUtils.newStringUtf8(Base64.decodeBase64(m.getPayload().getParts().get(0).getBody().getData()))); 给了我一个NullPointerException ...