HTTP GET請求返回Null？（JAVA）

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我用下面的代碼創建一個HTTP GET請求：HTTP GET請求返回Null？（JAVA）

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，可變inputLine顯示爲空值，在我的代碼導致一個NullPointerException。更糟的是，地址工作在我的瀏覽器罰款並返回此：

{"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":"abcdefghijklmnopqrstuvwxyz!~*.,/][()[email protected]#$%\"';:_`^&{}\\|<>?","tabHeader":"&8&lMineclad &r&9Network","tabFooter":"&7Mineclad.co"},"uuid":"559f6d32c2b740c9bc843dd54a55b39c"}

堆棧跟蹤：

[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)

我想知道：

爲什麼發生這種情況
而如何修復它

來源

2016-07-06 Bennett

請出示完整的堆棧跟蹤，並指示代碼行發生異常的地方。 –

在此代碼中，'inputLine'不可能爲null，而是在讀取循環結束時，您不再使用它。 – EJP

@EJP是的，這就是爲什麼我很困惑。 – Bennett

我相信不是

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

你想

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

你積累個人響應線到response，但隨後試圖從inputLine提取對象，這將永遠是null在這一點上。

來源

2016-07-06 16:30:03

您正在記錄inputLine但我假設您想要登錄response。

離開while循環inputLine必須是空的，因此這讓我難怪當您打印inputLine，你得到這一結果：

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

來源

2016-07-06 16:31:28 Robert

HTTP GET請求返回Null？ （JAVA）

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HTTP GET請求返回Null？（JAVA）