[英]Get all Cassandra query result in JSON format Using Java API
[英]How to get query result in Json form using Java API of Google Bigquery
一種選擇是將TO_JSON_STRING
函數應用於查詢結果。 例如,
#standardSQL
SELECT TO_JSON_STRING(t)
FROM (
SELECT x, y
FROM YourTable
WHERE z = 10
) AS t;
如果您希望表格的所有列都為JSON,則可以使用一種更簡單的形式:
#standardSQL
SELECT TO_JSON_STRING(t)
FROM YourTable AS t
WHERE z = 10;
我正在使用服務帳戶訪問BigQuery REST API以獲取JSON格式的響應。
為了使用服務帳戶,您將必須轉到憑據( https://console.cloud.google.com/apis/credentials )並選擇一個項目。
為您的項目創建一個服務帳戶,並以JSON格式下載機密文件。 將JSON文件保留在文件系統中,並設置其路徑。 檢查下圖以設置文件路徑:
因此,現在您要做的就是使用JAVA客戶端api來使用Big Query REST API。
這是我在項目中一直使用的簡單解決方案。
package com.example.bigquery;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
import org.apache.log4j.Logger;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.http.GenericUrl;
import com.google.api.client.http.HttpContent;
import com.google.api.client.http.HttpHeaders;
import com.google.api.client.http.HttpRequest;
import com.google.api.client.http.HttpRequestFactory;
import com.google.api.client.http.HttpResponse;
import com.google.api.client.http.HttpTransport;
import com.google.api.client.http.javanet.NetHttpTransport;
import com.google.api.client.http.json.JsonHttpContent;
import com.google.api.client.json.JsonFactory;
import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.common.io.CharStreams;
public class BigQueryDemo {
private static final String QUERY_URL_FORMAT = "https://www.googleapis.com/bigquery/v2/projects/%s/queries" + "?access_token=%s";
private static final String QUERY = "query";
private static final String QUERY_HACKER_NEWS_COMMENTS = "SELECT * FROM [bigquery-public-data:hacker_news.comments] LIMIT 1000";
private static final Logger logger = Logger.getLogger(BigQueryDemo.class);
static GoogleCredential credential = null;
static final HttpTransport HTTP_TRANSPORT = new NetHttpTransport();
static final JsonFactory JSON_FACTORY = new JacksonFactory();
static {
// Authenticate requests using Google Application Default credentials.
try {
credential = GoogleCredential.getApplicationDefault();
credential = credential.createScoped(Arrays.asList("https://www.googleapis.com/auth/bigquery"));
credential.refreshToken();
} catch (IOException e) {
e.printStackTrace();
}
}
public static void implicit() {
String projectId = credential.getServiceAccountProjectId();
String accessToken = generateAccessToken();
// Set the content of the request.
Dataset dataset = new Dataset().addLabel(QUERY, QUERY_HACKER_NEWS_COMMENTS);
HttpContent content = new JsonHttpContent(JSON_FACTORY, dataset.getLabels());
// Send the request to the BigQuery API.
GenericUrl url = new GenericUrl(String.format(QUERY_URL_FORMAT, projectId, accessToken));
logger.debug("URL: " + url.toString());
String responseJson = getQueryResult(content, url);
logger.debug(responseJson);
}
private static String getQueryResult(HttpContent content, GenericUrl url) {
String responseContent = null;
HttpRequestFactory requestFactory = HTTP_TRANSPORT.createRequestFactory();
HttpRequest request = null;
try {
request = requestFactory.buildPostRequest(url, content);
request.setParser(JSON_FACTORY.createJsonObjectParser());
request.setHeaders(
new HttpHeaders().set("X-HTTP-Method-Override", "POST").setContentType("application/json"));
HttpResponse response = request.execute();
InputStream is = response.getContent();
responseContent = CharStreams.toString(new InputStreamReader(is));
} catch (IOException e) {
logger.error(e);
}
return responseContent;
}
private static String generateAccessToken() {
String accessToken = null;
if ((System.currentTimeMillis() > credential.getExpirationTimeMilliseconds())) {
accessToken = credential.getRefreshToken();
} else {
accessToken = credential.getAccessToken();
}
System.out.println(accessToken);
return accessToken;
}
}
以下是Github的代碼鏈接: https : //github.com/vslala/BigQueryRestSample
這只是一個演示項目,可從BQ REST API提取JSON數據。 不要在項目中直接使用它。 如果您有任何疑問,請告訴我。
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