Using the Function interface to set a handler function in Java
You can set a handler function in Java by implementing the Function interface.
Warning
You should specify both values for the Function type parameters: the first one being the input argument type and the second one the type of the return value.
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;
// the Function has only one parameter type specified
// Handler should not have any type parameters (see the handler requirements)
public class Handler<T> implements Function<T, Integer> {
@Override
public Integer apply(T i) {
return 2;
}
}
import java.util.function.Function;
// Function does not have both parameter types 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 may have any access modifiers. If a field is non-public, writing getter/setter methods for it is optional.
Examples
HTTP request structure output
The following function receives a request with two fields (a string and a number) as an input and returns a formatted string with the data received.
Warning
To invoke the function, use the Yandex Cloud CLI or an HTTP request with the ?integration=raw parameter.
The Request.java file:
public class Request {
public String message;
public int number;
}
The Handler.java file:
import java.util.function.Function;
public class Handler implements Function<Request, String> {
@Override
public String apply(Request r) {
// at this stage, the r variable already stores the parsed query
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 using an HTTP request with the username, logs the request method and body, and returns a greeting.
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.
Note
In this example, to interpret JSON, we use a third-party library named org.json.
The Request.java file:
public class Request {
public String httpMethod;
public String body;
}
The Response.java file:
public class Response {
public int statusCode;
public String body;
public Response(int statusCode, String body) {
this.statusCode = statusCode;
this.body = body;
}
}
The Handler.java file:
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" parameter is obtained from the request body
// if you do not pass it, an error is 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