REST API 请求答案

【问题标题】：REST api requestREST API 请求
【发布时间】：2019-11-17 21:56:14
【问题描述】：

import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.Reader;
import java.io.StringReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

import javax.xml.parsers.DocumentBuilder;
import javax.xml.parsers.DocumentBuilderFactory;
import javax.xml.parsers.ParserConfigurationException;

import org.population.population.estimator.model.Country;
import org.w3c.dom.Document;
import org.w3c.dom.Node;
import org.xml.sax.InputSource;
import org.xml.sax.SAXException;

public class PopulationService {

public void getPopulation() {
String query_url = "https://data.opendatasoft.com/api/records/1.0/search/?dataset=world-population%40kapsarc&facet=country_name&facet=year&refine.country_name=Australia&refine.year=2000";

try {
            URL url = new URL(query_url);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(25000);
            conn.setRequestProperty("content-type","application/json; charset=utf-8");
            conn.setDoOutput(true);
            conn.setDoInput(true);
            conn.setRequestMethod("GET");
            conn.connect();

            OutputStream out = conn.getOutputStream();

            int status = conn.getResponseCode();
}  catch (Exception e) {
            System.out.println(e);
        }
    }
  public static void main(String args[]) {
    getPopulation();
  }
}

以下是显示异常详细信息的输出。

java.io.IOException：服务器返回 HTTP 响应代码：400 用于 URL： https://data.opendatasoft.com/api/records/1.0/search/?dataset=world-population%40kapsarc&facet=country_name&facet=year&refine.country_name=Australia&refine.year=2000

堆栈跟踪：

    at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
    at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
    at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
    at java.lang.reflect.Constructor.newInstance(Constructor.java:423)
    at sun.net.www.protocol.http.HttpURLConnection$10.run(HttpURLConnection.java:1890)
    at sun.net.www.protocol.http.HttpURLConnection$10.run(HttpURLConnection.java:1885)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.net.www.protocol.http.HttpURLConnection.getChainedException(HttpURLConnection.java:1884)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1457)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1441)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
    at org.population.population.estimator.service.PopulationService.getPopulation(PopulationService.java:55)
    at org.population.population.estimator.resources.PopulationResource.getPopulation(PopulationResource.java:20)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.glassfish.jersey.server.model.internal.ResourceMethodInvocationHandlerFactory$1.invoke(ResourceMethodInvocationHandlerFactory.java:81)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher$1.run(AbstractJavaResourceMethodDispatcher.java:143)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.invoke(AbstractJavaResourceMethodDispatcher.java:160)
    at org.glassfish.jersey.server.model.internal.JavaResourceMethodDispatcherProvider$TypeOutInvoker.doDispatch(JavaResourceMethodDispatcherProvider.java:203)
    at org.glassfish.jersey.server.model.internal.AbstractJavaResourceMethodDispatcher.dispatch(AbstractJavaResourceMethodDispatcher.java:97)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.invoke(ResourceMethodInvoker.java:389)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:347)
    at org.glassfish.jersey.server.model.ResourceMethodInvoker.apply(ResourceMethodInvoker.java:102)
    at org.glassfish.jersey.server.ServerRuntime$2.run(ServerRuntime.java:303)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:271)
    at org.glassfish.jersey.internal.Errors$1.call(Errors.java:267)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:315)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:297)
    at org.glassfish.jersey.internal.Errors.process(Errors.java:267)
    at org.glassfish.jersey.process.internal.RequestScope.runInScope(RequestScope.java:317)
    at org.glassfish.jersey.server.ServerRuntime.process(ServerRuntime.java:286)
    at org.glassfish.jersey.server.ApplicationHandler.handle(ApplicationHandler.java:1072)
    at org.glassfish.jersey.servlet.WebComponent.service(WebComponent.java:399)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:381)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:344)
    at org.glassfish.jersey.servlet.ServletContainer.service(ServletContainer.java:221)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:202)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:526)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92)
    at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:678)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343)
    at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408)
    at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
    at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:861)
    at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1579)
    at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1142)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:617)
    at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.io.IOException: Server returned HTTP response code: 400 for URL: https://data.opendatasoft.com/api/records/1.0/search/?dataset=world-population%40kapsarc&facet=country_name&facet=year&refine.country_name=Australia&refine.year=2000
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1840)
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1441)
    at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:480)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(HttpsURLConnectionImpl.java:338)
    at org.population.population.estimator.service.PopulationService.getPopulation(PopulationService.java:52)
    ... 48 more

只是将查询放在浏览器中会返回响应，但通过我的程序，我得到一个错误。如果有人可以帮助我将不胜感激。

我正在创建一个休息服务

【问题讨论】：

能否附上异常堆栈跟踪...
您需要找到 api 在响应中发送的确切错误消息。您可以修改代码以从错误流中获取消息，如下所示：HttpURLConnection httpConn = (HttpURLConnection)connection; InputStream is; if (httpConn.getResponseCode() >= 400) { is = httpConn.getErrorStream(); } else { is = httpConn.getInputStream(); }
删除OutputStream out = conn.getOutputStream();。由于您不想发送任何内容，因此没有理由打开 OutputStream。删除它解决了这个问题。设置内容类型也是无用的（而且是错误的）：GET 请求没有任何内容，因此它没有任何内容类型。
感谢您容忍我的，呃，新手。这太棒了，感谢您的宝贵时间。
@wuiiz93 这个 Java API 太可怕了。名字很糟糕，方法不直观。如果你真的需要编写很多这样的方法，我会考虑使用更现代的 HTTP 客户端库。

标签： java rest

【解决方案1】：

首先您必须使用 InputStream，因为您正在从响应中读取数据。其次，您必须接受 json 响应，因为您必须使用 conn.setRequestProperty("Accept", "application/json");

我修改了你的程序，请检查。

public class PopulationService {

  public static void getPopulation() {
    String query_url =
        "https://data.opendatasoft.com/api/records/1.0/search/?dataset=world-population@kapsarc&facet=country_name&facet=year&refine.country_name=Australia&refine.year=2000";

    try {
      URL url = new URL(query_url);
      HttpURLConnection conn = (HttpURLConnection) url.openConnection();
      conn.setRequestProperty("Accept", "application/json");
      conn.setDoOutput(true);
      conn.setRequestMethod("GET");
      conn.connect();

      BufferedReader br = new BufferedReader(new InputStreamReader(
              (conn.getInputStream())));
      String output;
      System.out.println("Response Server .... \n");
      while ((output = br.readLine()) != null) {
        System.out.println(output);
      }
      conn.disconnect();

      int status = conn.getResponseCode();
      System.out.println("Status Code: "+status);
    } catch (Exception e) {
      System.out.println(e);
    }
  }

  public static void main(String args[]) {
    getPopulation();
  }
}

【讨论】：