HTTP GET请求返回空？ （JAVA）

Question

我使用以下代码创建HTTP GET请求：

URL obj = new URL(pl.getConfig().getString("Database URL") + player.getName());
        HttpURLConnection con = (HttpURLConnection) obj.openConnection();
        BufferedReader in = new BufferedReader(
                new InputStreamReader(con.getInputStream()));
        String inputLine;
        StringBuffer response = new StringBuffer();

        while ((inputLine = in.readLine()) != null) {
            response.append(inputLine);
        }
        in.close();
        Logger.getLogger("Minecraft").info(inputLine); //Logs null

        Gson gsonData = new Gson();
        MinecladJson jsonData = gsonData.fromJson(inputLine, MinecladJson.class); //Returns null (because inputLine is null)
        PlayerData jsonPlayerData = jsonData.getPlayer(); //Crash here

不幸的是，变量inputLine似乎为null，导致我的代码中出现NullPointerException。更糟糕的是，该地址在我的浏览器中工作正常并返回：

{"player":{"balance":0,"permissions":["ultracosmetics.recievechest","ultracosmetics.openmenu"],"stats":{"playerKills":0,"deaths":0,"minutesPlayed":0},"achievements":{"firstJoin":false},"joinMessage":"&8[&9&l+&r&8] %r&7%p","leaveMessage":"&8[&9&l-&r&8] %r&7%p","rank":"default","firstJoin":"2016-07-01T02:37:14.458Z"},"content":{"chatFormat":"%r&7%p: %m","chatCensor":["testcensor"],"chatPrefixes":{"mage":"&5MAGE ","warrior":"&3WARRIOR ","chief":"&2CHIEF ","sage":"&7SAGE ","default":"","developer":"&9&lDEV ","moderator":"&6MOD "},"currencyName":"Coins","saveRate":30000,"cacheResetRate":1200000,"allowedCharacters":"abcdefghijklmnopqrstuvwxyz0123456789!~*.,/][()=+@#$%\"';:_`^&{}\\|<>?","tabHeader":"&8&lMineclad &r&9Network","tabFooter":"&7Mineclad.co"},"uuid":"559f6d32c2b740c9bc843dd54a55b39c"}

堆栈跟踪：

[09:16:54 WARN]: java.lang.NullPointerException
[09:16:54 WARN]:    at com.techurify.minecladPlugin.event.player.PlayerJoinListener.onPlayerJoin(PlayerJoinListener.java:56)
[09:16:54 WARN]:    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
[09:16:54 WARN]:    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
[09:16:54 WARN]:    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
[09:16:54 WARN]:    at java.lang.reflect.Method.invoke(Method.java:483)
[09:16:54 WARN]:    at org.bukkit.plugin.java.JavaPluginLoader$1.execute(JavaPluginLoader.java:300)
[09:16:54 WARN]:    at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:62)
[09:16:54 WARN]:    at org.bukkit.plugin.SimplePluginManager.fireEvent(SimplePluginManager.java:501)
[09:16:54 WARN]:    at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:486)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.PlayerList.onPlayerJoin(PlayerList.java:317)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.PlayerList.a(PlayerList.java:144)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.LoginListener.b(LoginListener.java:115)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.LoginListener.E_(LoginListener.java:53)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.NetworkManager.a(NetworkManager.java:224)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.ServerConnection.c(SourceFile:187)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.MinecraftServer.D(MinecraftServer.java:762)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.DedicatedServer.D(DedicatedServer.java:360)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.MinecraftServer.C(MinecraftServer.java:646)
[09:16:54 WARN]:    at net.minecraft.server.v1_10_R1.MinecraftServer.run(MinecraftServer.java:550)
[09:16:54 WARN]:    at java.lang.Thread.run(Thread.java:745)

我在想：

1. 为什么会这样？
2. 以及如何解决它

Answer 1

我相信而不是

MinecladJson jsonData = gsonData.fromJson(inputLine, MinecladJson.class);

你想要

MinecladJson jsonData = gsonData.fromJson(response.toString(), MinecladJson.class);
                                          ^^^^^^^^^^^^^^^^^^^

您已将个人回复行累积到response，但之后尝试从inputLine中提取对象，此时该对象始终为null。

Answer 2

您正在记录inputLine，但我认为您要记录response。

为了让while循环inputLine必须为null，因此当你打印inputLine时，我很难得到你的结果：

    StringBuffer response = new StringBuffer();

    while ((inputLine = in.readLine()) != null) { 
        // leave while loop if inputLine == in.readLine() == null

        response.append(inputLine);
    }
    in.close();
    Logger.getLogger("Minecraft").info(inputLine); //Logs null