Once you set up your project to declare the dependencies for your Google APIs Client Library for Java, follow these steps to make a request. The snippets in this page uses v3 of the Cloud Resource Manager API.
Step 1: Authentication
Instantiate com.google.auth.oauth2.GoogleCredentials
instance. For Google Cloud users, you may use GoogleCredentials.getApplicationDefault()
to get the Application Default Credentials
.
GoogleCredentials
credentials
=
GoogleCredentials
.
getApplicationDefault
();
For more information on authentication, refer to Google Auth Library Java .
Step 2: Instantiate Service Class
A Google service has one or more versions. A service class represents a version
of a service and is a child class of AbstractGoogleJsonClient
.
For example com.google.api.services.cloudresourcemanager.v3.CloudResourceManager
.
The builder class of the service class takes 3 parameters:
-
com.google.api.client.http.HttpTransport.GoogleNetHttpTransport.newTrustedTransport()creates an instance of it. -
com.google.api.client.json.JsonFactory.GsonFactory.getDefaultInstance()creates an instance of it. -
com.google.api.client.http.HttpRequestInitializer.new HttpCredentialsAdapter(credentials)gives an instance of it.
Also call setApplicationName()
method of the builder with your application
name. This sets the UserAgent header with the application name and is helpful
for troubleshooting with logs.
The code looks like:
HttpTransport
transport
=
GoogleNetHttpTransport
.
newTrustedTransport
();
JsonFactory
jsonFactory
=
GsonFactory
.
getDefaultInstance
();
CloudResourceManager
.
Builder
resourceManagerBuilder
=
new
CloudResourceManager
.
Builder
(
transport
,
jsonFactory
,
new
HttpCredentialsAdapter
(
credentials
))
.
setApplicationName
(
"Example Java App"
);
CloudResourceManager
cloudResourceManager
=
resourceManagerBuilder
.
build
();
Step 3: Create a Resource Object
A resource class represents a type of the resource managed by a service. The class is defined as an inner class of the service class. You can access them using the methods in the service class.
For example, you can get the "Projects" resource of the CloudResourceManager class:
import
com.google.api.services.cloudresourcemanager.v3.CloudResourceManager.Projects
;
...
Projects
projects
=
cloudResourceManager
.
projects
();
Step 4: Make a Request Object
The operations against the resource object are represented as request classes. The available operations depend on the resource class. For example, a resource class that provides "create", "get", and "delete" methods contain "Create", "Get", and "Delete" request classes respectively.
For Cloud Resource Manager's example, you can make the Get request object by
calling projects.get
method:
Get
get
=
projects
.
get
(
"projects/your-project-id"
);
Step 5: Execute the Request
A request object has the execute()
method that runs the request. This call
executes an HTTP request to the Google service and deserializes the JSON
response to a model class. For example, the execute()
method of the Get
request object returns a Project object:
Project
project
=
get
.
execute
();
System
.
out
.
println
(
"Project name: "
+
project
.
getDisplayName
());
Summary
With these steps, you can make requests using Google APIs Client Library for Java. Here is the code snippet that combines all the steps using the Resource Manager service.
package
com.example
;
import
com.google.api.client.googleapis.javanet.GoogleNetHttpTransport
;
import
com.google.api.client.http.HttpTransport
;
import
com.google.api.client.json.JsonFactory
;
import
com.google.api.client.json.gson.GsonFactory
;
import
com.google.api.services.cloudresourcemanager.v3.CloudResourceManager
;
import
com.google.api.services.cloudresourcemanager.v3.CloudResourceManager.Projects
;
import
com.google.api.services.cloudresourcemanager.v3.CloudResourceManager.Projects.Get
;
import
com.google.api.services.cloudresourcemanager.v3.model.Project
;
import
com.google.auth.http.HttpCredentialsAdapter
;
import
com.google.auth.oauth2.GoogleCredentials
;
public
class
ResourceManagerSample
{
public
static
void
main
(
String
[]
arguments
)
throws
Exception
{
GoogleCredentials
credentials
=
GoogleCredentials
.
getApplicationDefault
();
HttpTransport
transport
=
GoogleNetHttpTransport
.
newTrustedTransport
();
JsonFactory
jsonFactory
=
GsonFactory
.
getDefaultInstance
();
CloudResourceManager
.
Builder
resourceManagerBuilder
=
new
CloudResourceManager
.
Builder
(
transport
,
jsonFactory
,
new
HttpCredentialsAdapter
(
credentials
))
.
setApplicationName
(
"Example Java App"
);
CloudResourceManager
cloudResourceManager
=
resourceManagerBuilder
.
build
();
Projects
projects
=
cloudResourceManager
.
projects
();
Get
get
=
projects
.
get
(
"projects/your-project-id"
);
Project
project
=
get
.
execute
();
System
.
out
.
println
(
"Project display name: "
+
project
.
getDisplayName
());
}
}
