Java

Question

我正在 Java 中编写一些小代码片段，以便在移动应用程序后端服务器上运行。我使用的服务器有一个线程的限制，所以我写的代码基本上需要同步和单线程。

我正在使用 gson 解析从第三方 API 检索到的 JSON，一些示例代码如下：

public class JSONWorker {

    public double getJSONFromURL(String sURL){
        JsonParser jp = new JsonParser(); //from gson
        JsonElement root = null;

        // Connect to the URL using java's native library
        URL url = null;
        try {
            url = new URL(sURL);
        } catch (MalformedURLException e) {
            e.printStackTrace();
        }
        URLConnection request = null;
        try {
            request = url.openConnection();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            request.connect();
        } catch (IOException e) {
            e.printStackTrace();
        }
        try {
            root = jp.parse(new InputStreamReader((InputStream) request.getContent()));
        } catch (IOException e) {
            e.printStackTrace();
        }

        JsonObject rootobj = root.getAsJsonObject(); 
        String price = rootobj.get("lastPrice").getAsString(); 
        return Double.parseDouble(price);

    }
}

返回的错误表明我没有创建额外线程的权限，并指向此特定行作为问题：

root = jp.parse(new InputStreamReader((InputStream) request.getContent()));

gson 中的 JSON 解析器应该创建一个额外的线程是否正确？这可能与它在远程服务器上运行ning 这一事实有关吗？有没有办法强制 gson 或特别是解析器 synchronous/single 线程化？

编辑：完整错误输出

[ERROR] You have no permission to create thread in CodeRunner secure group.
java.lang.reflect.InvocationTargetException: null
    at sun.reflect.GeneratedMethodAccessor20.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.backendless.coderunner.runtime.task.TimerInvocationTask.runImpl(TimerInvocationTask.java:52)
    at com.backendless.coderunner.runtime.executor.ExtendedRunnable.run(ExtendedRunnable.java:39)
    at java.lang.Thread.run(Thread.java:748)
Caused by: java.security.AccessControlException: You have no permission to create thread in CodeRunner secure group.
    at com.backendless.coderunner.runtime.security.CodeRunnerSecurityManager.checkAccess(CodeRunnerSecurityManager.java:48)
    at java.lang.ThreadGroup.checkAccess(ThreadGroup.java:315)
    at java.lang.ThreadGroup.getParent(ThreadGroup.java:167)
    at sun.net.www.http.KeepAliveCache.run(KeepAliveCache.java:102)
    at sun.net.www.http.KeepAliveCache.run(KeepAliveCache.java:96)
    at java.security.AccessController.doPrivileged(Native Method)
    at sun.net.www.http.KeepAliveCache.put(KeepAliveCache.java:95)
    at sun.net.www.protocol.https.HttpsClient.putInKeepAliveCache(HttpsClient.java:659)
    at sun.net.www.http.HttpClient.finished(HttpClient.java:395)
    at sun.net.www.http.KeepAliveStream.close(KeepAliveStream.java:97)
    at sun.net.www.MeteredStream.justRead(MeteredStream.java:93)
    at sun.net.www.MeteredStream.read(MeteredStream.java:135)
    at java.io.FilterInputStream.read(FilterInputStream.java:133)
    at sun.net.www.protocol.http.HttpURLConnection$HttpInputStream.read(HttpURLConnection.java:3393)
    at sun.nio.cs.StreamDecoder.readBytes(StreamDecoder.java:284)
    at sun.nio.cs.StreamDecoder.implRead(StreamDecoder.java:326)
    at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:178)
    at java.io.InputStreamReader.read(InputStreamReader.java:184)
    at com.google.gson.stream.JsonReader.fillBuffer(JsonReader.java:1295)
    at com.google.gson.stream.JsonReader.nextNonWhitespace(JsonReader.java:1333)
    at com.google.gson.stream.JsonReader.consumeNonExecutePrefix(JsonReader.java:1576)
    at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:534)
    at com.google.gson.stream.JsonReader.peek(JsonReader.java:425)
    at com.google.gson.internal.Streams.parse(Streams.java:46)
    at com.google.gson.JsonParser.parse(JsonParser.java:84)
    at com.google.gson.JsonParser.parse(JsonParser.java:59)
    at com.myApp.timers.PriceGetterTimer.execute(PriceGetterTimer.java:100)
    ... 6 common frames omitted

干杯，米奇

Answer 1

这里的问题似乎不是 gson，而是 request.getContent()。

在许多情况下，将某种数据流转换为 InputStream 需要它自己的线程。也许数据是从网站流入的，并由网络通信层缓冲。使用线程可以最有效地实现将其即时转换为流。

Answer 2

话题由 built-in KeepAliveCache 创建。

您可以指定请求 header Connection 的值为 Close 或将系统属性 http.keepAlive 设置为值 false 像这样（在你实际打开连接之前）：

System.setProperty("http.keepAlive", "false");

可以找到更多信息here

Java - 阻止 GSON 创建一个额外的线程

Java - stop GSON from creating an additional thread

multithreading

backend

gson