This document provides steps to store data from a Java application in Google Cloud Storage. It describes how to 1) create a service account, download the private key file, and save the account details, and 2) develop a Java program to authenticate with the service account and make HTTP requests to Cloud Storage to list objects in a bucket. The Java code sets credentials using the service account private key, makes authenticated requests to Cloud Storage via the Google API client library, and prints the response.

1. GCS - Java to store data in Cloud Storage
目錄
目錄
Step1: 申請Service Account，並將相關資訊儲存起來
Step2: Java程式開發
Step1: 申請Service Account，並將相關資訊儲存起來
選擇Service Account，點選Create Client ID之後，系統會直接下載一個xxx­private.p12的檔案，該
檔案的密碼為”notasecret”，該密碼在需要做轉換pem檔案時候可以用到。

2.
建立好的Service Account大致如下：
其中Email address跟剛剛下載的*.p12檔案會在Java程式中用到
Step2: Java程式開發
Java程式說明如下：
前置參數設定：
/** Service Account 的 E­mail */
private static final String SERVICE_ACCOUNT_EMAIL =
"86083545333...tkhf@developer.gserviceaccount.com";
/** 欲列表的Bucket名稱，名稱即可，不用gs:// */
private static final String BUCKET_NAME = "yout­bucket­name";
/** p12檔案的位置，最好給訂絕對路徑 */
private static final String keypath = "path­to­your­privatekey2.p12";
設定credential相關參數
// 建制service account credential.
GoogleCredential credential = new GoogleCredential.Builder().setTransport(httpTransport)
.setJsonFactory(JSON_FACTORY)
.setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
.setServiceAccountScopes(Collections.singleton(STORAGE_SCOPE))

3. .setServiceAccountPrivateKeyFromP12File(new File(keypath))
.build();
透過HTTP Request來操作Cloud Storage
// 設定Request相關參數
String URI = "https://storage.googleapis.com/" + BUCKET_NAME;
HttpRequestFactory requestFactory = httpTransport.createRequestFactory(credential);
GenericUrl url = new GenericUrl(URI);
HttpRequest request = requestFactory.buildGetRequest(url);
HttpResponse response = request.execute();
String content = response.parseAsString();
// 設定要傳輸的參數
Source xmlInput = new StreamSource(new StringReader(content));
StreamResult xmlOutput = new StreamResult(new StringWriter());
Transformer transformer = TransformerFactory.newInstance().newTransformer();
transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "testing.dtd");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent­amount", "2");
transformer.transform(xmlInput, xmlOutput);
// 列印XML結果
System.out.println("nBucket listing for " + BUCKET_NAME + ":n");
System.out.println(xmlOutput.getWriter().toString());
完整程式記錄如下：
import java.io.File;
import java.io.IOException;
import java.io.StringReader;
import java.io.StringWriter;
import java.nio.charset.Charset;
import java.util.Collections;
import javax.xml.transform.OutputKeys;
import javax.xml.transform.Source;
import javax.xml.transform.Transformer;
import javax.xml.transform.TransformerFactory;
import javax.xml.transform.stream.StreamResult;
import javax.xml.transform.stream.StreamSource;
import com.google.api.client.googleapis.auth.oauth2.GoogleCredential;
import com.google.api.client.googleapis.javanet.GoogleNetHttpTransport;
import com.google.api.client.http.GenericUrl;
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.json.JsonFactory;

4. import com.google.api.client.json.jackson2.JacksonFactory;
import com.google.api.client.util.Preconditions;
import com.google.common.io.Files;
public class StorageServiceAccountSample {
/** Service Account 的 E­mail */
private static final String SERVICE_ACCOUNT_EMAIL =
"86083545333...tkhf@developer.gserviceaccount.com";
/** 欲列表的Bucket名稱，名稱即可，不用gs:// */
private static final String BUCKET_NAME = "yout­bucket­name";
private static final String keypath = "path­to­your­privatekey2.p12";
/** Google Cloud Storage OAuth 2.0 scope，這邊給予Read+Write權限 */
private static final String STORAGE_SCOPE =
"https://www.googleapis.com/auth/devstorage.read_write";
/** Global instance of the HTTP transport. */
private static HttpTransport httpTransport;
/** Global instance of the JSON factory. */
private static final JsonFactory JSON_FACTORY = JacksonFactory.getDefaultInstance();
public static void main(String[] args) {
try {
try {
httpTransport = GoogleNetHttpTransport.newTrustedTransport();
// 建制service account credential.
GoogleCredential credential = new GoogleCredential.Builder().setTransport(httpTransport)
.setJsonFactory(JSON_FACTORY)
.setServiceAccountId(SERVICE_ACCOUNT_EMAIL)
.setServiceAccountScopes(Collections.singleton(STORAGE_SCOPE))
.setServiceAccountPrivateKeyFromP12File(new File(keypath))
.build();
// Set up and execute Google Cloud Storage request.
String URI = "https://storage.googleapis.com/" + BUCKET_NAME;
HttpRequestFactory requestFactory = httpTransport.createRequestFactory(credential);
GenericUrl url = new GenericUrl(URI);
HttpRequest request = requestFactory.buildGetRequest(url);
HttpResponse response = request.execute();
String content = response.parseAsString();
// Instantiate transformer input
Source xmlInput = new StreamSource(new StringReader(content));
StreamResult xmlOutput = new StreamResult(new StringWriter());
// Configure transformer
Transformer transformer = TransformerFactory.newInstance().newTransformer(); // An
identity transformer
transformer.setOutputProperty(OutputKeys.DOCTYPE_SYSTEM, "testing.dtd");

5. transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty(OutputKeys.INDENT, "yes");
transformer.setOutputProperty("{http://xml.apache.org/xslt}indent­amount", "2");
transformer.transform(xmlInput, xmlOutput);
// Pretty print the output XML.
System.out.println("nBucket listing for " + BUCKET_NAME + ":n");
System.out.println(xmlOutput.getWriter().toString());
System.exit(0);
} catch (IOException e) {
System.err.println(e.getMessage());
}
} catch (Throwable t) {
t.printStackTrace();
}
System.exit(1);
}
}