Using the HttpServlet class to set a Java handler
You can define a Java handler by overriding the selected methods of the HttpServlet class.
Cloud Functions will automatically redirect each HTTP request to your handler depending on the HTTP method used to initiate the request. A GET request, for instance, will be redirected to your handler's doGet method, and POST, to doPost. For a redirect to be successful, these handler methods must exist, otherwise the function will return HTTP method XXX is not supported by this URL with code 405.
Unsupported methods
When using this model, please note that certain HttpServletRequest and HttpServletResponse methods are not supported by Cloud Functions.
HttpServletRequest:
- getAuthType
- getCookies
- upgrade
- authenticate
- login
- logout
- getContextPath
- getServletPath
- getPathTranslated
- getRealPath
- getRemotePort
- getLocalAddr
- getLocalPort
- getServerPort
- isUserInRole
- getUserPrincipal
- getRequestedSessionId
- getSession
- changeSessionId
- isRequestedSessionIdValid
- isRequestedSessionIdFromCookie
- isRequestedSessionIdFromURL
- isRequestedSessionIdFromUrl
HttpServletResponse:
- encodeURL
- encodeRedirectURL
- encodeUrl
- encodeRedirectUrl
Example of modeling various function behaviors when invoked using different HTTP methods
Warning
Do not use the ?integration=raw parameter to invoke this function. If you do, the function will not get any data about the original request's methods, headers, or parameters.
Cloud Functions supports Maven, which is a dependency management system for Java.
To create a function:
- Create a file named
Handler.javaat/src/main/java/Handler.javaand a file namedpom.xml. - Add the
/srcdirectory and thepom.xmlfile to a ZIP archive. - Upload the ZIP archive to Cloud Functions.
pom.xml file:
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>my.company.app</groupId>
<artifactId>servlet</artifactId>
<version>1</version>
<properties>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
<scope>compile</scope>
</dependency>
</dependencies>
</project>
Handler.java file:
import java.io.IOException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class Handler extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
// by setting the Content-Type to text/html, we let the browser render the HTML code
response.setContentType("text/html");
// displayed in bold when the function is invoked from the browser
response.getOutputStream().print("<b>Hello, world. In bold.</b>");
}
@Override
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws IOException {
var name = request.getParameter("name");
response.getWriter().println("Hello, " + name);
// the printWriter class returned by the getWriter method, make sure it's closed
response.getWriter().close();
}
}
Request examples:
GET method:
<b>Hello, world. In bold.</b>
Note
Running a GET request in a browser will display this string in bold without any tags because you had specified Content-Type: text/html in your handler's code.
POST method, name=Anonymous as your request parameter:
Hello, Anonymous
PUT method:
HTTP method PUT is not supported by this URL
Example of function information output
The following function outputs its metadata based on the call context.
pom.xml file:
<project>
<modelVersion>4.0.0</modelVersion>
<groupId>my.company.app</groupId>
<artifactId>servlet</artifactId>
<version>1</version>
<properties>
<maven.compiler.source>11</maven.compiler.source>
<maven.compiler.target>11</maven.compiler.target>
</properties>
<dependencies>
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>4.0.1</version>
<scope>compile</scope>
</dependency>
</dependencies>
</project>
Handler.java file:
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;
public class Handler extends HttpServlet {
@Override
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws IOException {
String requestId = request.getHeader("Lambda-Runtime-Aws-Request-Id");
String functionId = request.getHeader("Lambda-Runtime-Function-Name");
String versionId = request.getHeader("Lambda-Runtime-Function-Version");
String memoryLimit = request.getHeader("Lambda-Runtime-Memory-Limit");
String tokenJson = request.getHeader("Lambda-Runtime-Token-Json");
response.getOutputStream().print(String.format(
"RequestID: %s\n" +
"FunctionID: %s\n" +
"VersionID: %s\n" +
"MemoryLimit: %s\n" +
"TokenJSON: %s",
requestId,
functionId,
versionId,
memoryLimit,
tokenJson
));
}
}
Request example:
{
"httpMethod": "GET",
"requestContext": {},
"body": "",
"isBase64Encoded": true
}
Here is a response example:
{
"multiValueHeaders": {
"Content-Type": [
"application/json"
]
},
"isBase64Encoded": false,
"statusCode": 200,
"headers": {
"Content-Type": "application/json"
},
"body": "
RequestID: 6ccf3084-a92a-43a4-9122-5520********\n
FunctionID: b09hcbdla2ro********\n
VersionID: b09h91stkts4********\n
MemoryLimit: 1024\n
TokenJSON:
"
}