Using the Function interface to set a handler in Java
You can set a handler function in Java by implementing the Function interface.
Warning
You must specify both values for the Function type parameters: the first one being the input argument type and the second one, the return value type.
Example of a valid handler:
import java.util.function.Function;
public class Handler implements Function<Integer, String> {
@Override
public String apply(Integer i) {
return String.valueOf(i);
}
}
Examples of invalid handlers:
import java.util.function.Function;
// Function has only one parameter type specified.
// Handler should not have any parameter types (for details, see handler requirements)
public class Handler<T> implements Function<T, Integer> {
@Override
public Integer apply(T i) {
return 2;
}
}
import java.util.function.Function;
// Function has neither parameter type specified.
public class Handler implements Function {
@Override
public Object apply(Object i) {
return i;
}
}
You can use any classes as input and return types.
Note
Fields of these classes can have any access modifiers. For non-public fields, defining the getter or setter method is optional.
Examples
HTTP request structure output
The following function receives a request with two fields (a string and a number) and returns a formatted string with the provided data.
Warning
To invoke the function, use the Yandex Cloud CLI or an HTTP request with the ?integration=raw parameter.
Request.java:
public class Request {
public String message;
public int number;
}
Handler.java:
import java.util.function.Function;
public class Handler implements Function<Request, String> {
@Override
public String apply(Request r) {
// At this point, the r variable already stores the parsed request.
return String.format("Message is %s, number is %d", r.message, r.number);
}
}
Example of input data:
{
"message": "Hello",
"number": 24
}
Returned string:
Message is Hello, number is 24
Parsing an HTTP request
The function is invoked via an HTTP request with a username, logs the request method and body, and returns a greeting.
Warning
Do not use ?integration=raw to invoke this function. If you do, the function will not get any data about the original request’s methods, headers, or parameters.
Note
This example uses the org.json third-party library for JSON parsing.
Request.java:
public class Request {
public String httpMethod;
public String body;
}
Response.java:
public class Response {
public int statusCode;
public String body;
public Response(int statusCode, String body) {
this.statusCode = statusCode;
this.body = body;
}
}
Handler.java:
import java.util.function.Function;
import org.json.*;
public class Handler implements Function<Request, Response> {
@Override
public Response apply(Request r) {
var method = r.httpMethod;
var body = r.body;
System.out.println(String.format("%s, %s", method, body));
var jsonObject = new JSONObject(body);
// Here, the name value is retrieved from the request body.
// If you do not provide it, an error will be thrown.
var name = jsonObject.getString("name");
return new Response(200, String.format("Hello, %s", name));
}
}
Example of input data (the POST method):
{
"name": "Anonymous"
}
The log will contain the following:
POST, { "name": "Anonymous" }
Response returned:
Hello, Anonymous