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The following code is an example on how the REST API can be accessed from Java Code.

The code can be run with any java 11 JDK. For example: https://docs.aws.amazon.com/corretto/latest/corretto-11-ug/downloads-list.html

package com.mycompany.fews.webservices;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.StringWriter;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.List;
import java.util.stream.Collectors;

public class RestServiceClient {

    private RestServiceClient() {
    }

    public static void main(String[] args) throws IOException {

        // Example on how to call a GET request with parameters.
        filtersExample();

        // Example on how to run a workflow with a POST request with parameters.
        runTaskExample();

    }

    private static void filtersExample() throws IOException {
        String filtersUrl = "http://localhost:8080/FewsWebServices/rest/fewspiservice/v1/filters";
        List<RequestParameter> requestParameters = new ArrayList<>();
        requestParameters.add(new RequestParameter("documentFormat", "PI_XML"));
        HttpURLConnection connection = get(filtersUrl, requestParameters);
        if (connection.getResponseCode() == 200) {
            String response = getHttpResponse(connection);
            // the response contains the filters in PI_XML format.
            System.out.println(response);
        } else {
            // Handle error.
            String errorResponse = getHttpResponse(connection);
            System.out.println(errorResponse);
        }
    }

    private static void runTaskExample() throws IOException {
        String runTasksUrl = "http://localhost:8080/FewsWebServices/rest/fewspiservice/v1/runtask";
        List<RequestParameter> requestParameters = new ArrayList<>();
        List<RequestParameter> bodyParameters = new ArrayList<>();
        requestParameters.add(new RequestParameter("workflowId", "Import_Forecasts"));
        HttpURLConnection connection = post(runTasksUrl, requestParameters, bodyParameters);
        if (connection.getResponseCode() == 200) {
            String response = getHttpResponse(connection);
            // the response contains the task id.
            System.out.println(response);
        } else {
            // Handle error.
            String errorResponse = getHttpResponse(connection);
            System.out.println(errorResponse);
        }
    }

    public static HttpURLConnection post(String urlString, List<RequestParameter> requestParameters, List<RequestParameter> bodyParameters) throws IOException {
        URL url = createUrl(urlString, requestParameters);
        var connection = (HttpURLConnection) url.openConnection();
        connection.setRequestMethod("POST");
        connection.setDoOutput(true);
        connection.setDoInput(true);
        try (StringWriter stringWriter = new StringWriter(16)) {
            for (RequestParameter param : bodyParameters) {
                stringWriter.append(URLEncoder.encode(param.getKey(), StandardCharsets.UTF_8));
                stringWriter.append("=");
                stringWriter.append(URLEncoder.encode(param.getValue(), StandardCharsets.UTF_8));
                stringWriter.append("&");
            }
            connection.getOutputStream().write(stringWriter.toString().getBytes());
        }
        connection.connect();
        return connection;
    }

    public static HttpURLConnection get(String urlString, List<RequestParameter> requestParameters) throws IOException {
        URL url = createUrl(urlString, requestParameters);
        var connection = (HttpURLConnection) url.openConnection();
        configureTimeout(connection);
        return connection;
    }

    private static void configureTimeout(HttpURLConnection connection) {
        var connectionTimeout = 60_000;
        connection.setConnectTimeout(connectionTimeout);
        var readTimeout = 60_000;
        connection.setReadTimeout(readTimeout);
        connection.setDoInput(true);
    }

    private static URL createUrl(String urlString, List<RequestParameter> requestParameters) throws MalformedURLException {
        StringBuilder urlBuilder = new StringBuilder(16);
        urlBuilder.append(urlString);
        if (!requestParameters.isEmpty()) urlBuilder.append("?");
        for (var requestParam: requestParameters) {
            urlBuilder.append(URLEncoder.encode(requestParam.getKey(), StandardCharsets.UTF_8));
            urlBuilder.append("=");
            urlBuilder.append(URLEncoder.encode(requestParam.getValue(), StandardCharsets.UTF_8));
            urlBuilder.append("&");
        }
        return new URL(urlBuilder.toString());
    }

    public static String getHttpResponse(HttpURLConnection connection) throws IOException {
        try (var bufferedReader = new BufferedReader(new InputStreamReader(connection.getResponseCode() < HttpURLConnection.HTTP_BAD_REQUEST ? connection.getInputStream() : connection.getErrorStream(), StandardCharsets.UTF_8))) {
            return bufferedReader.lines().collect(Collectors.joining());
        }
    }

    private static class RequestParameter {
        private final String key;
        private final String value;

        private RequestParameter(String key, String value) {
            this.key = key;
            this.value = value;
        }

        private String getKey() {
            return key;
        }

        private String getValue() {
            return value;
        }

    }
}

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