Java Cursor类代码示例

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
/**
 * List all entities.
 *
 * @param cursor used for pagination to determine which page to return
 * @param limit  the maximum number of entries to return
 * @return a response that encapsulates the result list and the next page token/cursor
 */
@ApiMethod(
        name = "list",
        path = "user",
        httpMethod = ApiMethod.HttpMethod.GET)
public CollectionResponse<User> list(@Nullable @Named("cursor") String cursor, @Nullable @Named("limit") Integer limit) {
    limit = limit == null ? DEFAULT_LIST_LIMIT : limit;
    Query<User> query = ofy().load().type(User.class).limit(limit);
    if (cursor != null) {
        query = query.startAt(Cursor.fromWebSafeString(cursor));
    }
    QueryResultIterator<User> queryIterator = query.iterator();
    List<User> userList = new ArrayList<User>(limit);
    while (queryIterator.hasNext()) {
        userList.add(queryIterator.next());
    }
    return CollectionResponse.<User>builder().setItems(userList).setNextPageToken(queryIterator.getCursor().toWebSafeString()).build();
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
/**
 * List all entities.
 *
 * @param cursor used for pagination to determine which page to return
 * @param limit  the maximum number of entries to return
 * @return a response that encapsulates the result list and the next page token/cursor
 */
@ApiMethod(
        name = "list",
        path = "joke",
        httpMethod = ApiMethod.HttpMethod.GET)
public CollectionResponse<Joke> list(@Nullable @Named("cursor") String cursor, @Nullable @Named("limit") Integer limit) {
    Integer limitParam = limit == null ? DEFAULT_LIST_LIMIT : limit;
    Query<Joke> query = ofy().load().type(Joke.class).limit(limitParam);
    if (cursor != null) {
        query = query.startAt(Cursor.fromWebSafeString(cursor));
    }
    QueryResultIterator<Joke> queryIterator = query.iterator();
    List<Joke> jokeList = new ArrayList<>(limitParam);
    while (queryIterator.hasNext()) {
        jokeList.add(queryIterator.next());
    }
    return CollectionResponse.<Joke>builder().setItems(jokeList).setNextPageToken(queryIterator.getCursor().toWebSafeString()).build();
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
/**
 * List all entities.
 *
 * @param cursor used for pagination to determine which page to return
 * @param limit  the maximum number of entries to return
 * @return a response that encapsulates the result list and the next page token/cursor
 */
@ApiMethod(
        name = "list",
        path = "orders",
        httpMethod = ApiMethod.HttpMethod.GET)
public CollectionResponse<Orders> list(@Nullable @Named("cursor") String cursor, @Nullable @Named("limit") Integer limit) {
    limit = limit == null ? DEFAULT_LIST_LIMIT : limit;
    Query<Orders> query = ofy().load().type(Orders.class).limit(limit);
    if (cursor != null) {
        query = query.startAt(Cursor.fromWebSafeString(cursor));
    }
    QueryResultIterator<Orders> queryIterator = query.iterator();
    List<Orders> ordersList = new ArrayList<Orders>(limit);
    while (queryIterator.hasNext()) {
        ordersList.add(queryIterator.next());
    }
    return CollectionResponse.<Orders>builder().setItems(ordersList).setNextPageToken(queryIterator.getCursor().toWebSafeString()).build();
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
/**
 * List all entities.
 *
 * @param cursor used for pagination to determine which page to return
 * @param limit  the maximum number of entries to return
 * @return a response that encapsulates the result list and the next page token/cursor
 */
@ApiMethod(
        name = "list",
        path = "users",
        httpMethod = ApiMethod.HttpMethod.GET)
public CollectionResponse<Users> list(@Nullable @Named("cursor") String cursor, @Nullable @Named("limit") Integer limit) {
    limit = limit == null ? DEFAULT_LIST_LIMIT : limit;
    Query<Users> query = ofy().load().type(Users.class).limit(limit);
    if (cursor != null) {
        query = query.startAt(Cursor.fromWebSafeString(cursor));
    }
    QueryResultIterator<Users> queryIterator = query.iterator();
    List<Users> usersList = new ArrayList<Users>(limit);
    while (queryIterator.hasNext()) {
        usersList.add(queryIterator.next());
    }
    return CollectionResponse.<Users>builder().setItems(usersList).setNextPageToken(queryIterator.getCursor().toWebSafeString()).build();
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Override
public Result<Book> listBooks(String startCursorString) {
  FetchOptions fetchOptions = FetchOptions.Builder.withLimit(10); // Only show 10 at a time
  if (startCursorString != null && !startCursorString.equals("")) {
    fetchOptions.startCursor(Cursor.fromWebSafeString(startCursorString)); // Where we left off
  }
  Query query = new Query(BOOK_KIND) // We only care about Books
      .addSort(Book.TITLE, SortDirection.ASCENDING); // Use default Index "title"
  PreparedQuery preparedQuery = datastore.prepare(query);
  QueryResultIterator<Entity> results = preparedQuery.asQueryResultIterator(fetchOptions);

  List<Book> resultBooks = entitiesToBooks(results);     // Retrieve and convert Entities
  Cursor cursor = results.getCursor();              // Where to start next time
  if (cursor != null && resultBooks.size() == 10) {         // Are we paging? Save Cursor
    String cursorString = cursor.toWebSafeString();               // Cursors are WebSafe
    return new Result<>(resultBooks, cursorString);
  } else {
    return new Result<>(resultBooks);
  }
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Override
public Result<Book> listBooksByUser(String userId, String startCursorString) {
  FetchOptions fetchOptions = FetchOptions.Builder.withLimit(10); // Only show 10 at a time
  if (startCursorString != null && !startCursorString.equals("")) {
    fetchOptions.startCursor(Cursor.fromWebSafeString(startCursorString)); // Where we left off
  }
  Query query = new Query(BOOK_KIND) // We only care about Books
      // Only for this user
      .setFilter(new Query.FilterPredicate(
          Book.CREATED_BY_ID, Query.FilterOperator.EQUAL, userId))
      // a custom datastore index is required since you are filtering by one property
      // but ordering by another
      .addSort(Book.TITLE, SortDirection.ASCENDING);
  PreparedQuery preparedQuery = datastore.prepare(query);
  QueryResultIterator<Entity> results = preparedQuery.asQueryResultIterator(fetchOptions);

  List<Book> resultBooks = entitiesToBooks(results);     // Retrieve and convert Entities
  Cursor cursor = results.getCursor();              // Where to start next time
  if (cursor != null && resultBooks.size() == 10) {         // Are we paging? Save Cursor
    String cursorString = cursor.toWebSafeString();               // Cursors are WebSafe
    return new Result<>(resultBooks, cursorString);
  } else {
    return new Result<>(resultBooks);
  }
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
/**
 * Counts the entities returned by the specified query.
 * @param ds    reference to the datastore service
 * @param query query whose results to count
 * @return the number of entities returned by the query
 */
public static int countEntities( final DatastoreService ds, final com.google.appengine.api.datastore.Query q ) {
	q.setKeysOnly();
	
	final int          batchSize    = 1000;
	final FetchOptions fetchOptions = FetchOptions.Builder.withLimit( batchSize );
	
	Cursor cursor = null;
	int    count  = 0;
	while ( true ) {
		if ( cursor != null )
			fetchOptions.startCursor( cursor );
		
		final QueryResultList< Entity > resultList = ds.prepare( q ).asQueryResultList( fetchOptions );
		
		count += resultList.size();
		
		if ( resultList.size() < batchSize )
			return count;
		
		cursor = resultList.getCursor();
	}
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Test
public void testCursor() throws Exception {
    Entity parent = createTestEntityWithUniqueMethodNameKey("Person", "testKeysOnly");
    Key key = parent.getKey();

    Entity john = createEntity("Person", key)
        .withProperty("name", "John")
        .withProperty("surname", "Doe")
        .store();

    Query query = new Query("Person")
        .setAncestor(key)
        .setKeysOnly();

    PreparedQuery preparedQuery = service.prepare(query);
    QueryResultIterator<Entity> iter = preparedQuery.asQueryResultIterator();
    Assert.assertNotNull(iter.next());
    Cursor cursor = iter.getCursor();

    iter = service.prepare(query).asQueryResultIterator(FetchOptions.Builder.withStartCursor(cursor));
    Assert.assertFalse(iter.hasNext());
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Test
public void testSort() {
    int onePage = 6;
    Query query = new Query(kindName, rootKey);
    query.addSort("name", Query.SortDirection.ASCENDING);
    // fetch first page   aa,aa,aa,aa,aa,aa
    Cursor cursor = checkPage(query, null, null, onePage, onePage, testDat[0], testDat[0]);
    Cursor decodedCursor = Cursor.fromWebSafeString(cursor.toWebSafeString());
    // fetch next page    aa,aa,aa,aa,bb,bb
    checkPage(query, decodedCursor, null, onePage, onePage, testDat[0], testDat[1]);

    // desc
    onePage = total / testDat.length;
    query = new Query(kindName, rootKey);
    query.addSort("name", Query.SortDirection.DESCENDING);
    // fetch first page   jj,jj,........,jj,jj
    String chkChar = testDat[testDat.length - 1];
    cursor = checkPage(query, null, null, onePage, onePage, chkChar, chkChar);
    decodedCursor = Cursor.fromWebSafeString(cursor.toWebSafeString());
    // fetch next page   ii,ii,........,ii,ii
    chkChar = testDat[testDat.length - 2];
    checkPage(query, decodedCursor, null, onePage, onePage, chkChar, chkChar);
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Test
public void testStartEndCursor() {
    int limit = total / testDat.length;
    Query query = new Query(kindName, rootKey);
    query.addSort("name", Query.SortDirection.ASCENDING);
    FetchOptions fetchOption = FetchOptions.Builder.withLimit(limit);
    // fetch 1st page and get cursor1
    QueryResultList<Entity> nextBatch = service.prepare(query)
        .asQueryResultList(fetchOption);
    Cursor cursor1 = Cursor.fromWebSafeString(nextBatch.getCursor().toWebSafeString());
    // fetch 2nd page and get cursor2
    nextBatch = service.prepare(query).asQueryResultList(fetchOption.startCursor(cursor1));
    Cursor cursor2 = Cursor.fromWebSafeString(nextBatch.getCursor().toWebSafeString());
    // cursor1 as start and cursor2 as end and 15 in limit -- -- should return 2nd page.
    checkPage(query, cursor1, cursor2, limit, limit, testDat[1], testDat[1]);
    // cursor1 as start and cursor2 as end and 30 in limit -- should return 2nd page.
    checkPage(query, cursor1, cursor2, 2 * limit, limit, testDat[1], testDat[1]);
    // cursor2 as start and cursor1 as end and 15 in limit -- should not return any.
    checkPage(query, cursor2, cursor1, limit, 0, null, null);
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
private Cursor checkPage(Query query, Cursor stCursor, Cursor endCursor, int limit, int exptRet,
                         String chkSt, String chkEnd) {
    FetchOptions fetchOption = FetchOptions.Builder.withLimit(limit);
    if (stCursor != null) {
        fetchOption = fetchOption.startCursor(stCursor);
    }
    if (endCursor != null) {
        fetchOption = fetchOption.endCursor(endCursor);
    }
    QueryResultList<Entity> nextBatch = service.prepare(query)
        .asQueryResultList(fetchOption);
    assertEquals(exptRet, nextBatch.size());
    if (chkSt != null) {
        assertEquals(chkSt, nextBatch.get(0).getProperty("name"));
    }
    if (chkEnd != null) {
        assertEquals(chkEnd, nextBatch.get(nextBatch.size() - 1).getProperty("name"));
    }
    return nextBatch.getCursor();
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Nullable
public static PagingInfo create(@Nullable Cursor afterCursor, int limit, boolean moreResults,
    UriInfo uriInfo) {
  String afterCursorStr = (afterCursor == null) ? "" : afterCursor.toWebSafeString();
  if (afterCursorStr.isEmpty()) {
    return null;
  } else {
    String nextUrl;
    if (moreResults) {
      Multimap<String, String> queryParams = toMultimap(uriInfo.getQueryParameters());
      queryParams.replaceValues(AFTER_CURSOR_PARAM, asList(afterCursorStr));
      queryParams.replaceValues(LIMIT_PARAM, asList(String.valueOf(limit)));
      nextUrl = URLUtil.buildURL(uriInfo.getAbsolutePath(), queryParams);
    } else {
      nextUrl = null;
    }
    return new PagingInfo(nextUrl, afterCursorStr);
  }
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
private Builder(Class<T> resourceClass, @Nullable UriInfo uriInfo,
    @Nullable MultivaluedMap<String, String> queryParams, int defaultLimit) {
  if (uriInfo != null) {
    queryParams = uriInfo.getQueryParameters();
  }
  this.resourceClass = resourceClass;
  this.uriInfo = uriInfo;
  String afterCursorStr = queryParams.getFirst(PagingInfo.AFTER_CURSOR_PARAM);
  if (afterCursorStr != null) {
    afterCursor = Cursor.fromWebSafeString(afterCursorStr);
  } else {
    afterCursor = null;
  }
  limit = queryParams.containsKey(PagingInfo.LIMIT_PARAM) ?
      Integer.valueOf(queryParams.getFirst(PagingInfo.LIMIT_PARAM)) : defaultLimit;
  if (limit <= 0) {
    throw ErrorResponseMsg.createException("limit must be greater than zero",
      ErrorInfo.Type.BAD_REQUEST);
  }
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@Override public Cursor getCursor() throws PermanentFailure, RetryableFailure {
  return safeRun(new Evaluater<Cursor>() {
    @Override public Cursor run() {
      return iterator.getCursor();
    }
  });
}
 

import com.google.appengine.api.datastore.Cursor; //导入依赖的package包/类
@ApiMethod(name = "listUsers")
public CollectionResponse<Users> listQuote(@Nullable @com.google.api.server.spi.config.Named("cursor") String cursorString,
                                           @Nullable @com.google.api.server.spi.config.Named("count") Integer count) {

    Query<Users> query = ofy().load().type(Users.class);
    if (count != null) query.limit(count);
    if (cursorString != null && cursorString != "") {
        query = query.startAt(Cursor.fromWebSafeString(cursorString));
    }
    List<Users> records = new ArrayList<Users>();
    QueryResultIterator<Users> iterator = query.iterator();
    int num = 0;
    while (iterator.hasNext()) {
        records.add(iterator.next());
        if (count != null) {
            num++;
            if (num == count) break;
        }
    }
    //Find the next cursor
    if (cursorString != null && cursorString != "") {
        Cursor cursor = iterator.getCursor();
        if (cursor != null) {
            cursorString = cursor.toWebSafeString();
        }
    }
    return CollectionResponse.<Users>builder().setItems(records).setNextPageToken(cursorString).build();
}