我一直在研究这个问题而且我已经达到了一个我不知道该怎么办的地步。我想要做的是使用一个类下载并将文件解析为字符串，然后将该字符串发送到另一个类来解析JSON的东西。所有部件都可以自行工作，我已经分别测试了所有部件。我只是不知道如何将值发送到Json解析以开始解析。
所以这是我的filedownloader类。
public class JsonFileDownloader extends AsyncTask<String, Void, String> {
//used to access the website
String username = "admin";
String password = "admin";
public String ret = "";
@Override
protected String doInBackground(String... params) {
Log.d("Params ", params[0].toString());
readFromFile(params[0]);
return ret;
}
private String readFromFile(String myWebpage) {
HttpURLConnection urlConnection = null;
try {
//Get the url connection
URL url = new URL(myWebpage);
Authenticator.setDefault(new Authenticator() {
@Override
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(username, password.toCharArray());
}
});
urlConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
if (inputStream != null) {
ret = streamToString(inputStream);
inputStream.close();
Log.d("Final String", ret);
}
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
return ret;
}
}
public static String streamToString(InputStream is) throws IOException {
StringBuilder sb = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
String line;
while ((line = rd.readLine()) != null) {
sb.append(line);
}
return sb.toString();
}
public String getJsonData()
{
return ret;
}
}
这样可以正常我一遍又一遍地测试它没有错误。 接下来是Json解析器，就像这样。
public class JSONParser {
JSONObject jsonResponse;
String jsonData;
//Consturctor
public JSONParser()
{
//this.jsonData = jsonData;
// this.OutputData = outPutData;
}
public void parsesData(String promo,
ArrayList<String> pictureHTTP,
ArrayList<String> pathHTTP,
ArrayList<String> labelText) throws IOException {
//Build the Json String
JsonFileDownloader jfd = new JsonFileDownloader();
// jsonData = String.valueOf(jfd.execute(promo));
jfd.execute(promo);
//jfd.getResuts(jsonData);
//jsonData = jfd.ret;
Log.d("JsonData String = " , jsonData);
//Try to parse the data
try
{
Log.d("Jsondata " , jsonData);
//Creaate a new JSONObject ith the name/value mapping from the JSON string
jsonResponse = new JSONObject(jsonData);
//Returns the value mapped by the name if it exists and is a JSONArry
JSONArray jsonMainNode = jsonResponse.optJSONArray("");
//Proccess the JSON node
int lenghtJsonArrar = jsonMainNode.length();
for (int i = 0; i<lenghtJsonArrar; i++)
{
//Get object for each json node
JSONObject jsonChildNode = jsonMainNode.getJSONObject(i);
//Get the node values
//int song_id = Integer.parseInt(jsonChildNode.optString("song_id").toString());
String picture = jsonChildNode.optString("picture").toString();
String pathName = jsonChildNode.optString("path").toString();
String lableName = jsonChildNode.optString("label".toString());
//Debug Testing code
pictureHTTP.add(picture);
pathHTTP.add(pathName);
labelText.add(lableName);
}
} catch (JSONException e) {
e.printStackTrace();
}
}
现在我知道问题出在哪里了。当我尝试为jsonData分配一个值时，它永远不会被分配，因此它为null并且系统失败。 我在jfd.exicute（）之后尝试过一些东西，但我不知道如何从最终的字符串输出中获取值到jsonData中。 感谢您对此的任何帮助。
答案 0 :(得分：3)
好的，这是一个非常灵活的模式，用于使用AsyncTask下载Web内容并将结果从UI线程返回到UI线程。
步骤1 定义一个接口，该接口将充当AsyncTask与您想要数据的位置之间的消息总线。
public interface AsyncResponse<T> {
void onResponse(T response);
}
第2步：创建一个通用的AsyncTask扩展，它将获取任何URL并从中返回结果。你基本上已经有了这个，但我做了一些调整。最重要的是，允许设置AsyncResponse回调接口。
public class WebDownloadTask extends AsyncTask<String, Void, String> {
private AsyncResponse<String> callback;
// Optional parameters
private String username;
private String password;
// Make a constuctor to store the parameters
public WebDownloadTask(String username, String password) {
this.username = username;
this.password = password;
}
// Don't forget to call this
public void setCallback(AsyncResponse<String> callback) {
this.callback = callback;
}
@Override
protected String doInBackground(String... params) {
String url = params[0];
return readFromFile(url);
}
@Override
protected void onPostExecute(String s) {
super.onPostExecute(s);
if (callback != null) {
callback.onResponse(s);
} else {
Log.w(WebDownloadTask.class.getSimpleName(), "The response was ignored");
}
}
/******* private helper methods *******/
private String streamToString(InputStream is) throws IOException {
StringBuilder sb = new StringBuilder();
BufferedReader rd = new BufferedReader(new InputStreamReader(is));
String line;
while ((line = rd.readLine()) != null) {
sb.append(line);
}
return sb.toString();
}
private String readFromFile(String myWebpage) {
String response = null;
HttpURLConnection urlConnection = null;
try {
//Get the url connection
URL url = new URL(myWebpage);
// Unnecessary for general AsyncTask usage
/*
Authenticator.setDefault(new Authenticator() {
@Override
protected PasswordAuthentication getPasswordAuthentication() {
return new PasswordAuthentication(username, password.toCharArray());
}
});
*/
urlConnection = (HttpURLConnection) url.openConnection();
InputStream inputStream = urlConnection.getInputStream();
if (inputStream != null) {
response = streamToString(inputStream);
inputStream.close();
Log.d("Final String", response);
}
} catch (IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
}
return response;
}
}
第3步前进并在任何地方使用AsyncTask。这是一个例子。请注意，如果您不使用setCallback，则无法获取来自AsyncTask的数据。
public class MainActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
WebDownloadTask task = new WebDownloadTask("username", "password");
task.setCallback(new AsyncResponse<String>() {
@Override
public void onResponse(String response) {
// Handle response here. E.g. parse into a JSON object
// Then put objects into some list, then place into an adapter...
Toast.makeText(getApplicationContext(), response, Toast.LENGTH_SHORT).show();
}
});
// Use any URL, this one returns a list of 10 users in JSON
task.execute("http://jsonplaceholder.typicode.com/users");
}
}