我一直在使用Gson在API中解析JSON以在我的应用中使用。这是JSON输出的一个示例：
{"getdashboarddata":{"version":"1.0.0","runtime":492.3939704895,"data":{"raw":{"personal":{"hashrate":0},"pool":{"hashrate":1705841},"network":{"hashrate":41430764.301,"esttimeperblock":94.464466565347,"nextdifficulty":578.78109116,"blocksuntildiffchange":1}},"personal":{"hashrate":0,"sharerate":"0.0000","sharedifficulty":0,"shares":{"valid":0,"invalid":0,"invalid_percent":0,"unpaid":0},"estimates":{"block":0,"fee":0,"donation":0,"payout":0}},"pool":{"info":{"name":"RAPIDHASH","currency":"DOGE"},"workers":2199,"hashrate":1.705841,"shares":{"valid":1866290,"invalid":15564,"invalid_percent":0.83,"estimated":1866214,"progress":100},"price":"0.00000073","difficulty":32,"target_bits":21},"system":{"load":[0.1,0.25,0.29]},"network":{"hashrate":41.430764301,"difficulty":911.23745057,"block":235378,"esttimeperblock":94.46,"nextdifficulty":578.78109116,"blocksuntildiffchange":1}}}}
这是logcat：
05-25 17:12:00.230 24143-24159/io.kd.figgycity50.mpos.mposchecker E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: io.kd.figgycity50.mpos.mposchecker, PID: 24143
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: com.google.gson.JsonSyntaxException: java.io.EOFException: End of input at line 1 column 501
at com.google.gson.Gson.fromJson(Gson.java:813)
at com.google.gson.Gson.fromJson(Gson.java:768)
at com.google.gson.Gson.fromJson(Gson.java:717)
at com.google.gson.Gson.fromJson(Gson.java:689)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:77)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:64)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.io.EOFException: End of input at line 1 column 501
at com.google.gson.stream.JsonReader.nextNonWhitespace(JsonReader.java:1377)
at com.google.gson.stream.JsonReader.doPeek(JsonReader.java:471)
at com.google.gson.stream.JsonReader.skipValue(JsonReader.java:1209)
at com.google.gson.internal.bind.ReflectiveTypeAdapterFactory$Adapter.read(ReflectiveTypeAdapterFactory.java:170)
at com.google.gson.Gson.fromJson(Gson.java:803)
at com.google.gson.Gson.fromJson(Gson.java:768)
at com.google.gson.Gson.fromJson(Gson.java:717)
at com.google.gson.Gson.fromJson(Gson.java:689)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:77)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:64)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
这是获取并解析JSON的代码：
private class DownloadWebpageTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... urls) {
// params comes from the execute() call: params[0] is the url.
String resp = null;
try {
resp = downloadUrl(urls[0]);
} catch (IOException e) {
resp = "{\"getdashboarddata\":{\"data\":{\"personal\":{\"hashrate\":0},\"pool\":{\"info\":{\"name\":\"SET POOL IN SETTINGS\",\"currency\":\"???\"},\"hashrate\":0,\"difficulty\":0},\"network\":{\"hashrate\":0,\"difficulty\":0}}}}";
}
Gson gson = new Gson();
Log.d("INFO", resp);
MPOSDashStruct data = gson.fromJson(resp, MPOSDashStruct.class);
TextView t = (TextView)findViewById(R.id.poolName);
TextView t2 = (TextView)findViewById(R.id.khashMe);
TextView t3 = (TextView)findViewById(R.id.khashPool);
TextView t4 = (TextView)findViewById(R.id.khashNet);
t.setText(data.getName());
t2.setText(data.getMyHash());
t3.setText(data.getPoolHash());
t4.setText(data.getNetHash());
return "Hello World. If you see this, you probably hack. Get out.";
}
private String downloadUrl(String myurl) throws IOException {
InputStream is = null;
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
try {
URL url = new URL(myurl);
HttpURLConnection conn = (HttpURLConnection) url.openConnection();
conn.setReadTimeout(10000 /* milliseconds */);
conn.setConnectTimeout(15000 /* milliseconds */);
conn.setRequestMethod("GET");
conn.setDoInput(true);
// Starts the query
conn.connect();
int response = conn.getResponseCode();
is = conn.getInputStream();
// Convert the InputStream into a string
String contentAsString = readIt(is, len);
return contentAsString;
// Makes sure that the InputStream is closed after the app is
// finished using it.
} finally {
if (is != null) {
is.close();
}
}
}
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len];
reader.read(buffer);
return new String(buffer);
}
}
}
这是MPOSDashStruct类：
package io.kd.figgycity50.mpos.mposchecker;
import com.google.gson.annotations.SerializedName;
/**
* Created by George on 25/05/2014.
*/
public class MPOSDashStruct {
public static class getdashboarddata {
public static class data {
public static class personal {
public static int hashrate;
}
public static class pool {
public static int hashrate;
public static int difficulty;
public static class info {
@SerializedName("name")
public static String poolName;
public static String currency;
}
}
public static class network {
public static int hashrate;
public static int difficulty;
}
}
}
public String getName() {
return getdashboarddata.data.pool.info.poolName;
}
public String getCurrency() {
return getdashboarddata.data.pool.info.currency;
}
public int getPoolHash() {
return getdashboarddata.data.pool.hashrate;
}
public int getPoolDiff() {
return getdashboarddata.data.pool.difficulty;
}
public int getMyHash() {
return getdashboarddata.data.personal.hashrate;
}
public int getNetHash() {
return getdashboarddata.data.network.hashrate;
}
}
代码似乎很好，Android Studio没有错误。
编辑2：contentAsString输出
05-25 17:30:12.976 29974-29988/io.kd.figgycity50.mpos.mposchecker D/INFO﹕ {"getdashboarddata":{"version":"1.0.0","runtime":632.7919960022,"data":{"raw":{"personal":{"hashrate":0},"pool":{"hashrate":1675289},"network":{"hashrate":38541151.201,"esttimeperblock":61.161346587453,"nextdifficulty":538.41366248,"blocksuntildiffchange":1}},"personal":{"hashrate":0,"sharerate":"0.0000","sharedifficulty":0,"shares":{"valid":0,"invalid":0,"invalid_percent":0,"unpaid":0},"estimates":{"block":0,"fee":0,"donation":0,"payout":0}},"pool":{"info":{"name":"RAPIDHASH","currency":"DOGE"}
使用Log.d（“INFO”，contentAsString）
编辑：使用getContentLength后，新的logcat是这样的：
05-25 17:50:19.203 5143-5157/io.kd.figgycity50.mpos.mposchecker W/dalvikvm﹕ threadid=11: thread exiting with uncaught exception (group=0x41bd4ba8)
05-25 17:50:19.203 5143-5157/io.kd.figgycity50.mpos.mposchecker E/AndroidRuntime﹕ FATAL EXCEPTION: AsyncTask #1
Process: io.kd.figgycity50.mpos.mposchecker, PID: 5143
java.lang.RuntimeException: An error occured while executing doInBackground()
at android.os.AsyncTask$3.done(AsyncTask.java:300)
at java.util.concurrent.FutureTask.finishCompletion(FutureTask.java:355)
at java.util.concurrent.FutureTask.setException(FutureTask.java:222)
at java.util.concurrent.FutureTask.run(FutureTask.java:242)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
Caused by: java.lang.NegativeArraySizeException: -1
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.readIt(MainActivity.java:120)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.downloadUrl(MainActivity.java:104)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:71)
at io.kd.figgycity50.mpos.mposchecker.MainActivity$DownloadWebpageTask.doInBackground(MainActivity.java:64)
at android.os.AsyncTask$2.call(AsyncTask.java:288)
at java.util.concurrent.FutureTask.run(FutureTask.java:237)
at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:231)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
at java.lang.Thread.run(Thread.java:841)
指向我的代码行：
public String readIt(InputStream stream, int len) throws IOException, UnsupportedEncodingException {
Reader reader = null;
reader = new InputStreamReader(stream, "UTF-8");
char[] buffer = new char[len]; //this line, others added so you can understand
reader.read(buffer);
return new String(buffer);
}
编辑3：指导Gson处理读者工作得很好，但又出现了新的错误。 logcat的：
05-26 09:17:52.459 11810-11810/io.kd.figgycity50.mpos.mposchecker E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: io.kd.figgycity50.mpos.mposchecker, PID: 11810
java.lang.RuntimeException: Unable to start activity ComponentInfo{io.kd.figgycity50.mpos.mposchecker/io.kd.figgycity50.mpos.mposchecker.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2195)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at io.kd.figgycity50.mpos.mposchecker.MainActivity.onCreate(MainActivity.java:49)
at android.app.Activity.performCreate(Activity.java:5231)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2159)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2245)
at android.app.ActivityThread.access$800(ActivityThread.java:135)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:136)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
指向：
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
SharedPreferences sharedPref = PreferenceManager.getDefaultSharedPreferences(this);
String prefPool = sharedPref.getString("pref_pool", "https://doge.rapidhash.net/");
String prefKey = sharedPref.getString("pref_key", "XXXX");
new DownloadWebpageTask().execute(prefPool + "index.php?page=api&action=getdashboarddata&api_key=" + prefKey);
TextView t = (TextView)findViewById(R.id.poolName); // this line
TextView t2 = (TextView)findViewById(R.id.khashMe);
TextView t3 = (TextView)findViewById(R.id.khashPool);
TextView t4 = (TextView)findViewById(R.id.khashNet);
t.setText(dashStruct.getName());
t2.setText(dashStruct.getMyHash());
t3.setText(dashStruct.getPoolHash());
t4.setText(dashStruct.getNetHash());
}
答案 0 :(得分：2)
我不知道你为什么要这样做
// Only display the first 500 characters of the retrieved
// web page content.
int len = 500;
如果您的JSON比这长，那么您将其分解为JSON解析器无法解析的部分。阅读完整的JSON字符串。
从回复中获取content length。
int len = conn.getContentLength();
答案 1 :(得分：1)
从上面Edit 3开始，以下行似乎正在抛出NullPointerException：
t.setText(dashStruct.getName());
我可以告诉您将dashStruct声明为在AsyncTask DownloadWebpageTask中初始化的类级变量。
按照设计，AsyncTask将在主线程上执行（确切地说，AsyncTask＃doInBackground（T）方法）。如果DownloadWebpageTask在主线程执行dashStruct时尚未完成初始化t.setText(dashStruct.getName()); - 将抛出NPE - dashStruct为空。
要通过此例外，请覆盖onPostExecute()中的DownloadWebpageTask并将以下代码移至该处（将其从onCreate(Bundle)中删除）：
@Override
protected void onPostExecute(String result) {
if (dashStruct != null) {
t.setText(dashStruct.getName());
t2.setText(dashStruct.getMyHash());
t3.setText(dashStruct.getPoolHash());
t4.setText(dashStruct.getNetHash());
} else {
// Deal with dashStruct being null
}
}
我注意到在原始帖子中，您正在更新DownloadWebpageTask#doInBackground(String...)中的用户界面（设置文本视图文字）。这将抛出IllegalStateException，因为doInBackground()是从主线程处理的 - 唯一允许触摸UI的线程。 onPostExecute()在主线程上处理。这就是你的UI逻辑应该去的地方。