java无法从URLConnection获取JSON响应

Question

我正在尝试使用JavaURLConnection读取来自googleapi的响应

在浏览器中，如果我查询 “https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobilez”

我得到JSON格式的响应

{
 "error": {
  "errors": [
   {
    "domain": "global",
    "reason": "invalidParameter",
    "message": "Invalid string value: 'mobilez'. Allowed values: [desktop, mobile]",
    "locationType": "parameter",
    "location": "strategy"
   }
  ],
  "code": 400,
  "message": "Invalid string value: 'mobilez'. Allowed values: [desktop, mobile]"
 }
}

但是当我使用下面的代码时

URL url = null;
            System.setProperty("http.agent", "");

            url = new URL("https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobilez");//"https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=" + paramUrl + "&strategy=" + paramStrategy);
            URLConnection conn = url.openConnection();
            conn.setRequestProperty("Accept", "application/json");
            conn.setRequestProperty("User-Agent", "Mozilla/5.0");
            BufferedReader br = new BufferedReader(new InputStreamReader(conn.getInputStream()));
            String strTemp = "";
            StringBuilder sb = new StringBuilder();

            while ((null != (strTemp = br.readLine())))
            {
                sb.append(strTemp);
                if (dump)
                {
                    System.out.println(strTemp);
                }
            }

我得到IO异常

java.io.IOException: Server returned HTTP response code: 400 for URL: https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobilez
    at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1627)
    at sun.net.www.protocol.https.HttpsURLConnectionImpl.getInputStream(HttpsURLConnectionImpl.java:254)
    at amirTest.PageSpeedCheck.main(PageSpeedCheck.java:62)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:606)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:144)

/但我需要得到JSON响应

请告诉我需要做什么更改才能得到JSON作为响应

Answer 1

谢谢@JB Nizet

它在我尝试读取错误流时起作用

            InputStream is = null;
            if (conn.getResponseCode() == 400)
            {

                is = conn.getErrorStream();
                error = true;
            } else
            {
                is = conn.getInputStream();
            }

Answer 2

将连接强制转换为Http（s）URLConnection，并在出现错误时调用getErrorStream()以获取流

Answer 3

API调用中使用的参数错误，因此服务器正在重新运行状态代码400。这意味着这是一个错误的要求

mobilz应该是移动的。此外，您使用的url不正确

Answer 4

您只需按以下方式更改代码：

    BufferedReader reader = new BufferedReader(new InputStreamReader(((HttpURLConnection) (new URL("https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobilez")).openConnection())
.getInputStream(), Charset.forName("UTF-8")));

见原始答案here

参见以下类似的SO问题：

URLConnection Error - java.io.IOException: Server returned HTTP response code: 400 for URL

Server returned HTTP response code: 400

Answer 5

对于：400：

您正在以移动z而不是移动发送策略

改变

https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobilez

到

https://www.googleapis.com/pagespeedonline/v2/runPagespeed?url=https%3A%2F%2Fwww.zauq.se&strategy=mobile

请注意URL末尾的z

获取JSON响应：

参考：How to Parse this JSON Response in JAVA