Java：在JSON中响应的简单HTTP服务器应用程序

Question

我想用Java创建一个非常简单的HTTP服务器应用程序。

例如，如果我在localhost端口8080上运行服务器，并且从浏览器发出以下调用，我希望获得一个带有字符串“hello world！”的Json数组：

http://localhost:8080/func1?param1=123&param2=456

我希望在服务器中有类似这样的东西（非常抽象的代码）：

// Retunrs JSON String
String func1(String param1, String param2) {
    // Do Something with the params
    String jsonFormattedResponse = "['hello world!']";

    return jsonFormattedResponse;
}

我想这个函数实际上不应该“返回”json，而是使用某种HTTP响应处理程序或类似的东西发送它...

最简单的方法是什么，而不需要熟悉许多具有特殊功能和方法的第三方库？

Answer 1

您可以使用com.sun.net.httpserver包中的类：

import com.sun.net.httpserver.Headers;
import com.sun.net.httpserver.HttpServer;
import java.io.IOException;
import java.io.UnsupportedEncodingException;
import java.net.InetSocketAddress;
import java.net.URI;
import java.net.URLDecoder;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
import java.util.ArrayList;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Map;

public class JsonServer {
    private static final String HOSTNAME = "localhost";
    private static final int PORT = 8080;
    private static final int BACKLOG = 1;

    private static final String HEADER_ALLOW = "Allow";
    private static final String HEADER_CONTENT_TYPE = "Content-Type";

    private static final Charset CHARSET = StandardCharsets.UTF_8;

    private static final int STATUS_OK = 200;
    private static final int STATUS_METHOD_NOT_ALLOWED = 405;

    private static final int NO_RESPONSE_LENGTH = -1;

    private static final String METHOD_GET = "GET";
    private static final String METHOD_OPTIONS = "OPTIONS";
    private static final String ALLOWED_METHODS = METHOD_GET + "," + METHOD_OPTIONS;

    public static void main(final String... args) throws IOException {
        final HttpServer server = HttpServer.create(new InetSocketAddress(HOSTNAME, PORT), BACKLOG);
        server.createContext("/func1", he -> {
            try {
                final Headers headers = he.getResponseHeaders();
                final String requestMethod = he.getRequestMethod().toUpperCase();
                switch (requestMethod) {
                    case METHOD_GET:
                        final Map<String, List<String>> requestParameters = getRequestParameters(he.getRequestURI());
                        // do something with the request parameters
                        final String responseBody = "['hello world!']";
                        headers.set(HEADER_CONTENT_TYPE, String.format("application/json; charset=%s", CHARSET));
                        final byte[] rawResponseBody = responseBody.getBytes(CHARSET);
                        he.sendResponseHeaders(STATUS_OK, rawResponseBody.length);
                        he.getResponseBody().write(rawResponseBody);
                        break;
                    case METHOD_OPTIONS:
                        headers.set(HEADER_ALLOW, ALLOWED_METHODS);
                        he.sendResponseHeaders(STATUS_OK, NO_RESPONSE_LENGTH);
                        break;
                    default:
                        headers.set(HEADER_ALLOW, ALLOWED_METHODS);
                        he.sendResponseHeaders(STATUS_METHOD_NOT_ALLOWED, NO_RESPONSE_LENGTH);
                        break;
                }
            } finally {
                he.close();
            }
        });
        server.start();
    }

    private static Map<String, List<String>> getRequestParameters(final URI requestUri) {
        final Map<String, List<String>> requestParameters = new LinkedHashMap<>();
        final String requestQuery = requestUri.getRawQuery();
        if (requestQuery != null) {
            final String[] rawRequestParameters = requestQuery.split("[&;]", -1);
            for (final String rawRequestParameter : rawRequestParameters) {
                final String[] requestParameter = rawRequestParameter.split("=", 2);
                final String requestParameterName = decodeUrlComponent(requestParameter[0]);
                requestParameters.putIfAbsent(requestParameterName, new ArrayList<>());
                final String requestParameterValue = requestParameter.length > 1 ? decodeUrlComponent(requestParameter[1]) : null;
                requestParameters.get(requestParameterName).add(requestParameterValue);
            }
        }
        return requestParameters;
    }

    private static String decodeUrlComponent(final String urlComponent) {
        try {
            return URLDecoder.decode(urlComponent, CHARSET.name());
        } catch (final UnsupportedEncodingException ex) {
            throw new InternalError(ex);
        }
    }
}