Blogger

Developer's Guide: Java

The Blogger Data API allows client applications to view and update Blogger content in the form of Google Data API feeds.

Your client application can use the Blogger Data API to create new blog posts, edit or delete existing blog posts, and query for blog posts that match particular criteria.

In addition to providing some background on the capabilities of the Blogger Data API, this document provides examples of basic Data API interactions using the Java client library. If you're interested in understanding more about the underlying protocol that the library uses, see the Protocol section of this developer's guide.

Contents

Audience

This document is intended for programmers who want to write Java client applications that can interact with Blogger.

This document assumes that you understand the general ideas behind the Google Data APIs protocol.

For reference information about the classes and methods provided by the client library, see the Java client library API reference. For general Blogger Data API reference information, see the Protocol reference guide.

Getting started

For help setting up the client library, see the Getting Started Guide.

The Java client library requires Java 1.5. After downloading the client library, you'll find the classes you need to get started in the java/lib/gdataclient-1.0.jar file.

Creating a Blogger account

You may want to sign up for a Blogger account for testing purposes. Blogger uses Google Accounts, so if you already have a Google account, you're all set.

Running the sample code

A full working sample client, containing all the sample code shown in this document, is available in the Java client library distribution, under the directory gdata/java/sample/blogger/BloggerClient.java. Build and execution instructions are included in the same directory in the README.txt file.

The sample client performs several operations on the provided blog to demonstrate the use of the Blogger Data API.

To compile the examples in this document into your own code, you'll need the following import statements:

import com.google.gdata.client.*;
import com.google.gdata.data.*;
import com.google.gdata.util.*;
import java.io.IOException;
import java.net.URL;

Authenticating to the Blogger service

You can access both public and private feeds using the Blogger Data API. Public feeds don't require any authentication, but they are read-only. If you want to modify blogs, then your client needs to authenticate before requesting private feeds. It can authenticate using any of three approaches: OAuth authentication, AuthSub proxy authentication or ClientLogin username/password authentication.

For more information about authentication with Google Data APIs in general, see the authentication documentation.

Most of the samples in subsequent sections of this document assume you have an authenticated GoogleService object.

OAuth authentication

For documentation about OAuth authentication using the Java GData library, please see OAuth in the Google Data Protocol Client Libraries.

AuthSub proxy authentication

AuthSub proxy authentication is used by web applications that need to authenticate their users to Google Accounts. The website operator and the client code don't have access to the username and password for the Blogger user; instead, the client obtains special AuthSub tokens that allow the client to act on a particular user's behalf. For more detailed information, see the AuthSub documentation.

When a user first visits your application, they have not yet been authenticated. In this case, you need to display some information and a link directing the user to a Google page to authenticate your request for access to their blogs. The Java client library provides a function to generate the Google page's URL. The code below retrieves the URL of the AuthSubRequest page:

String next = "http://www.example.com/welcome.html";
String scope = "http://www.blogger.com/feeds/";
boolean secure = false;
boolean session = true;
String authSubLogin = AuthSubUtil.getRequestUrl(next, scope, secure, session);

The getRequestUrl method takes the following parameters (corresponding to the query parameters used by the AuthSubRequest handler):

next
The URL of the page that Google should redirect the user to after authentication.
scope
Indicates that the application is requesting a token to access Blogger feeds. The scope string to use is http://www.blogger.com/feeds/ (URL-encoded, of course).
secure
Indicates whether the client is requesting a secure token.
session
Indicates whether the token returned can be exchanged for a multi-use (session) token.

The above example shows a call that doesn't request a secure token (the value of secure is false). The resulting request URL might look like this:

https://www.google.com/accounts/AuthSubRequest?scope=http%3A%2F%2Fwww.blogger.com%2Ffeeds%2F&session=1&secure=0&next=http%3A%2F%2Fwww.example.com%2Fwelcome.html

The user follows the link to Google's site and authenticates to their Google Account.

After the user authenticates, the AuthSub system redirects them to the URL you specified in the next query parameter of the AuthSubRequest URL. The AuthSub system appends an authentication token to that URL, as the value of the token query parameter. For example:

http://www.example.com/welcome.html?token=yourAuthToken

This token value represents a single-use AuthSub token. In this example, since session = true was specified, this token can be exchanged for an AuthSub session token by calling the AuthSubSessionToken service, as follows, where urlFromAuthSub is the URL that AuthSub appended the token to:

String token = AuthSubUtil.getTokenFromReply(urlFromAuthSub);
String sessionToken = AuthSubUtil.exchangeForSessionToken(token, null);

That is, you pass your one-time-use token to the exchangeForSessionToken method, along with either null (for unregistered mode) or a private key (for registered mode), and the AuthSub interface returns a session token. For more information about registered applications and private keys, see the "Signing requests" section of the AuthSub documentation.

Your application can then use the session token in subsequent interactions with Blogger. To tell the Java client library to automatically send the session token with each request, call the GoogleService object's setAuthSubToken method:

GoogleService.setAuthSubToken(sessionToken, null);

After that, the client library automatically sends the token along with every request.

ClientLogin username/password authentication

Use ClientLogin authentication if your client is a standalone, single-user "installed" client (such as a desktop application). Just call the setUserCredentials method on your GoogleService object and all subsequent interactions with Blogger will be authenticated:

GoogleService myService = new GoogleService("blogger", "exampleCo-exampleApp-1");
myService.setUserCredentials("user@example.com", "secretPassword");

In the snippet above, we pass two parameters to the GoogleService constructor. The first parameter is the name of the service we want to interact with. The second parameter is the name of our application in the form companyName-applicationName-versionID.

For more information about ClientLogin authentication, including sample requests and responses, see the Authentication for Installed Applications documentation.

Note: Use the same token for all requests in a given session; don't acquire a new token for each Blogger request.

Note: As described in the ClientLogin documentation, the authentication request may fail and request a CAPTCHA challenge. If you want Google to issue and handle the CAPTCHA challenge, then send the user to https://www.google.com/accounts/DisplayUnlockCaptcha?service=blogger (rather than to the CAPTCHA-handling URL given in the ClientLogin documentation).

Retrieving a list of blogs

The Blogger Data API provides a feed that lists the blogs for a particular user; that feed is known as a "metafeed."

The following sample code uses an authenticated GoogleService object to retrieve the metafeed and then prints each blog's title.

public static void printUserBlogs(GoogleService myService)
    throws ServiceException, IOException {

  // Request the feed
  final URL feedUrl = new URL("http://www.blogger.com/feeds/default/blogs");
  Feed resultFeed = myService.getFeed(feedUrl, Feed.class);

  // Print the results
  System.out.println(resultFeed.getTitle().getPlainText());
  for (int i = 0; i < resultFeed.getEntries().size(); i++) {
    Entry entry = resultFeed.getEntries().get(i);
    System.out.println("\t" + entry.getTitle().getPlainText());
  }
}

Note the URL used by the getFeed method. This is the default metafeed URL; it returns a list of blogs for the currently authenticated user. To access a feed for a different user, you can put the user's ID in place of default in the metafeed URL. The user's ID is the string of digits at the end of the user's profile URL.

Creating posts

The Blogger Data API allows you to create and publish new blog entries, as well as creating drafts of entries.

Note: Setting a custom author for posts is currently not supported. All new posts will appear as if they were created by the currently authenticated user.

Publishing a blog post

You can use the Java client library to publish new blog entries.

First, create an Entry object to represent the blog post. Then you can set the title, content and other attributes of the blog post. Finally, use the GoogleService object to insert the post. Here's an example of how to publish a new blog post:

public static Entry createPost(
    GoogleService myService, String blogID, String title,
    String content, String userName)
    throws ServiceException, IOException {
  // Create the entry to insert
  Entry myEntry = new Entry();
  myEntry.setTitle(new PlainTextConstruct(title));
  myEntry.setContent(new PlainTextConstruct(content));

  // Ask the service to insert the new entry
  URL postUrl = new URL("http://www.blogger.com/feeds/" + blogID + "/posts/default");
  return myService.insert(postUrl, myEntry);
}

The insert method takes the service's post URL as a parameter. Then the method returns the entry as it was stored by Blogger. The entry returned is the same one you sent, but it also contains various elements added by Blogger, such as a post ID.

If your request fails for some reason, Blogger may return a different status code. For information about the status codes, see the Google Data API protocol reference document.

Creating a draft blog post

Draft posts are created in the same way as public posts, but you need to set the draft attribute of the Entry object. You can create a blog post like the one above as a draft by adding the highlighted line:

public static Entry createPost(GoogleService myService, String blogId,
    String title, String content, String userName,
    Boolean isDraft)
    throws ServiceException, IOException {
  // Create the entry to insert
  Entry myEntry = new Entry();
  myEntry.setTitle(new PlainTextConstruct(title));
  myEntry.setContent(new PlainTextConstruct(content));
  myEntry.setDraft(isDraft);

  // Ask the service to insert the new entry
  URL postUrl = new URL("http://www.blogger.com/feeds/" + blogID + "/posts/default");
  return myService.insert(postUrl, myEntry);
}

You can turn an existing draft blog post into a published post by retrieving the draft post, setting the draft attribute to false, and then updating the post. We'll cover retrieving and updating posts in the next two sections.

Retrieving posts

The following sections describe how to retrieve a list of blog posts, with and without query parameters.

You can query a Blogger public feed without authentication. Therefore, you don't need to call the setUserCredentials method or do AuthSub authentication before retrieving posts from a public blog.

Retrieving all blog posts

To retrieve the user's posts, call the same getFeed method used to retrieve the blogs metafeed, but this time send the blog-post feed URL:

public static void printAllPosts(
    GoogleService myService, String blogId)
    throws ServiceException, IOException {
  // Request the feed
  URL feedUrl = new URL("http://www.blogger.com/feeds/" + blogID + "/posts/default");
  Feed resultFeed = myService.getFeed(feedUrl, Feed.class);

  // Print the results
  System.out.println(resultFeed.getTitle().getPlainText());
  for (int i = 0; i < resultFeed.getEntries().size(); i++) {
    Entry entry = resultFeed.getEntries().get(i);
    System.out.println("\t" + entry.getTitle().getPlainText());
  }
  System.out.println();
}

Retrieving posts using query parameters

The Blogger Data API lets you request a set of entries that match specified criteria, such as requesting blog posts published or updated in a given date range. To do this, you create a Query object and pass it to the GoogleService.getQuery method.

For example, to send a date-range query, use the setPublishedMin and setPublishedMax methods of the Query object. The following code snippet prints the title of each blog post published between the given start time and end time:

public static void printDateRangeQueryResults(
    GoogleService myService, String blogId,
    DateTime startTime, DateTime endTime)
    throws ServiceException, IOException {
  // Create query and submit a request
  URL feedUrl = new URL("http://www.blogger.com/feeds/" + blogID + "/posts/default");
  Query myQuery = new Query(feedUrl);
  myQuery.setPublishedMin(startTime);
  myQuery.setPublishedMax(endTime);
  Feed resultFeed = myService.query(myQuery, Feed.class);

  // Print the results
  System.out.println(resultFeed.getTitle().getPlainText() +
      " posts between " + startTime + " and " + endTime);
  for (int i = 0; i < resultFeed.getEntries().size(); i++) {
    Entry entry = resultFeed.getEntries().get(i);
    System.out.println("\t" + entry.getTitle().getPlainText());
    System.out.println("\t" + entry.getUpdated().toStringRfc822());
  }
  System.out.println();
}

Notice that the Query object is constructed using the same post feed URL used to retrieve posts.

The Blogger Data API supports the following Query methods:

addCategoryFilter
Specify categories (also known as labels) to filter the feed results. For example, http://www.blogger.com/feeds/blogID/posts/default/-/Fritz/Laurie returns entries with both the labels Fritz and Laurie.
setMaxResults
Set the maximum number of entries to return.
setPublishedMin, setPublishedMax
Set the bounds on entry publication dates.
setStartIndex
Set the 1-based index of the first result to be retrieved (for paging).
setUpdatedMin, setUpdatedMax
Set the bounds on entry update dates. These query parameters are ignored unless the orderby parameter is set to updated.

Note: There are currently no setters for the orderby query parameter. However, you can still use the Query.addCustomParameter() method if you need to set this.

For more information about query parameters, see the Blogger Data API Reference Guide and the Google Data APIs Reference Guide.

Updating posts

To update an existing blog post, first you retrieve the entry you want to update, then you modify it, and then you send it to Blogger using the update method. The following code snippet modifies the title of a blog entry, assuming that you've already retrieved the entry from the server.

public static Entry updatePostTitle(
    GoogleService myService, Entry entryToUpdate, String newTitle)
    throws ServiceException, IOException {
  entryToUpdate.setTitle(new PlainTextConstruct(newTitle));
  URL editUrl = new URL(entryToUpdate.getEditLink().getHref());
  return myService.update(editUrl, entryToUpdate);
}

The above code returns an Entry containing the entire newly-updated post. To update any other properties, simply set them in the Entry object before calling update.

Note: Modifying the author data associated with posts is currently not supported.

Deleting posts

To delete a post, pass the post's edit URL to the delete method on your GoogleService object, like this:

public static void deletePost(
    GoogleService myService, String editLinkHref)
    throws ServiceException, IOException {
  URL deleteUrl = new URL(editLinkHref);
  myService.delete(deleteUrl);
}

Comments

The Blogger Data API allows for creating, retrieving, and deleting comments. Updating comments is not supported (nor is it available in the web interface).

Creating comments

To post a comment, create an Entry object and insert it as follows:

public static Entry createComment(
    GoogleService myService, String blogID, String postId,
    String commentText)
    throws ServiceException, IOException {
  // Build the comment feed URI
  String commentsFeedUri = "http://www.blogger.com/feeds/" + blogID + "/" + postId + "/comments/default";
  URL feedUrl = new URL(commentsFeedUri);

  // Create a new entry for the comment and submit it to the GoogleService
  Entry myEntry = new Entry();
  myEntry.setContent(new PlainTextConstruct(commentText));
  return myService.insert(feedUrl, myEntry);
}

Note: Currently, you can only post comments to a blog owned by the authenticated user.

Note: Setting a custom author for comments is currently not supported. All new comments will appear as if they were created by the currently authenticated user.

Retrieving comments

You can retrieve the comments for a particular post from the post's comments feed URL:

public static void printAllComments(
    GoogleService myService, String blogID, String postId)
    throws ServiceException, IOException {
  // Build comment feed URI and request comments on the specified post
  String commentsFeedUri = "http://www.blogger.com/feeds/" + blogID + "/" + postId + "/comments/default";
  URL feedUrl = new URL(commentsFeedUri);
  Feed resultFeed = myService.getFeed(feedUrl, Feed.class);

  // Display the results
  System.out.println(resultFeed.getTitle().getPlainText());
  for (int i = 0; i < resultFeed.getEntries().size(); i++) {
    Entry entry = resultFeed.getEntries().get(i);
    System.out.println("\t" +
        ((TextContent) entry.getContent()).getContent().getPlainText());
    System.out.println("\t" + entry.getUpdated().toStringRfc822());
  }
  System.out.println();
}

Or you can get the comments from all posts by using the blog's comments feed URL:

http://www.blogger.com/feeds/blogID/comments/default

Deleting comments

To delete a comment, pass the comment's edit URL to the delete method on your GoogleService object like this:

public static void deleteComment(GoogleService myService, String editLinkHref)
    throws ServiceException, IOException {
  URL deleteUrl = new URL(editLinkHref);
  myService.delete(deleteUrl);
}

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