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• Android Volley从URL示例获取JSON数据

在本教程中，我们将使用Volley库从URL提取JSON数据。 Volley是一个HTTP库，为我们应用程序的网络连接提供了便利。
【Android从url获取json数据的volley库】使用Volley库的优点如下：

• 更舒适，更快的请求管理。
• 它提供了有效的网络管理。

Android Volley从URL示例获取JSON数据在此示例中，我们将使用Volley库从URL加载JSON数据。 JSON数据包含教程的字符串“名称”，字符串“ imageurl”和字符串“ description”。从URL提取数据后，它们将显示在ListView中。你可以在https://www.srcmini.com/android-json-parsing-tutorial上参考有关JSON解析教程的更多信息。
让我们创建一个包含以下信息的JSON数据。
URL处的JSON数据（提供你的信息URL）= http://192.168.1.35:8080/jsondata/

{ "tutorials":[ { "name":"Java", "imageurl":"https://www.srcmini.com/images/logo/javahome.png", "description":"Java is a high level, robust, object-oriented and secure programming language." }, { "name":"Android", "imageurl":"https://www.srcmini.com/images/logo/androidhome.png", "description":"Android is a complete set of software for mobile devices." }, { "name":"Python", "imageurl":"https://www.srcmini.com/images/logo/pythonhome.png", "description":"Python is a general purpose, dynamic, high level and interpreted programming language." }, { "name":"C++", "imageurl":"https://www.srcmini.com/cpp/images/cpp-home.png", "description":"C++ is an object-oriented programming language." } ] }

JSON数据如下所示：

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在布局中创建一个activity_main.xml并添加以下代码。
activity_main.xml

< ?xml version="1.0" encoding="utf-8"?> < android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="example.srcmini.com.volleyreadimagejson.MainActivity">< ListView android:id="@+id/listView" android:layout_width="match_parent" android:layout_height="match_parent" android:layout_marginBottom="8dp" android:layout_marginEnd="8dp" android:layout_marginStart="8dp" android:layout_marginTop="8dp" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" />< ProgressBar android:id="@+id/progressBar" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:layout_marginBottom="292dp" android:layout_marginEnd="8dp" android:layout_marginStart="8dp" android:layout_marginTop="8dp" android:visibility="gone" app:layout_constraintBottom_toBottomOf="parent" app:layout_constraintEnd_toEndOf="parent" app:layout_constraintStart_toStartOf="parent" app:layout_constraintTop_toTopOf="parent" />< /android.support.constraint.ConstraintLayout>

现在，在布局目录中创建一个list_item.xml文件，其中包含ListView的行项目。它包含一个用于图像显示的ImageView和两个用于文本显示的TextView。
list_item.xml

< ?xml version="1.0" encoding="utf-8"?> < LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:padding="16dp" android:orientation="vertical"> < LinearLayout android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="horizontal"> < ImageView android:id="@+id/imageView" android:layout_width="50dp" android:layout_height="50dp" android:src="http://www.srcmini.com/@drawable/placeholder" android:contentDescription="image view" /> < TextView android:id="@+id/textViewName" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="title" android:textAppearance="@style/Base.TextAppearance.AppCompat.Large" /> < /LinearLayout>< TextView android:id="@+id/textViewImageUrl" android:layout_width="match_parent" android:layout_height="wrap_content" android:text="url" android:autoLink="web" android:textColor="#08308e" />< /LinearLayout>

创建一个名称为Tutorial.java且信息为字符串“ name”，字符串“ imageurl”和字符串“ description”的数据模型类。
Tutorial.java

package example.srcmini.com.volleyreadimagejson; public class Tutorial { String name, imageUrl, description; public Tutorial(String name, String imageUrl, String description) { this.name = name; this.imageUrl = imageUrl; this.description = description; } public String getName() { return name; } public String getImageUrl() { return imageUrl; } public String getDescription() { return description; } }

创建一个名为MyAdapter.java的自定义适配器类，并扩展ArrayAdapter来处理自定义ListView。在此类中，我们将匿名类称为new ImageDownloaderTask（holder.imageView）.execute（imageUrl）以从URL下载图像。
MyAdapter.java

package example.srcmini.com.volleyreadimagejson; import android.app.ProgressDialog; import android.content.Context; import android.graphics.Bitmap; import android.view.LayoutInflater; import android.view.View; import android.view.ViewGroup; import android.widget.ArrayAdapter; import android.widget.ImageView; import android.widget.TextView; import java.util.List; public class MyAdapter extends ArrayAdapter< Tutorial> { //the tutorial list that will be displayed private List< Tutorial> tutorialList; private Bitmap bitmap; private Context mCtx; //here we are getting the tutoriallist and context //so while creating the object of this adapter class we need to give tutoriallist and context public MyAdapter(List< Tutorial> tutorialList, Context mCtx) { super(mCtx, R.layout.list_item, tutorialList); this.tutorialList = tutorialList; this.mCtx = mCtx; }//this method will return the list item @Override public View getView(int position, View convertView, ViewGroup parent) { //getting the layoutinflater ViewHolder holder; LayoutInflater inflater = LayoutInflater.from(mCtx); convertView = inflater.inflate(R.layout.list_item, null, true); holder = new ViewHolder(); //getting text views holder.textViewName = convertView.findViewById(R.id.textViewName); holder.textDescription = convertView.findViewById(R.id.textViewImageUrl); holder.imageView = convertView.findViewById(R.id.imageView); convertView.setTag(holder); //Getting the tutorial for the specified position Tutorial tutorial = tutorialList.get(position); String imageUrl = tutorial.getImageUrl(); String tutorialDescription = tutorial.getDescription(); String tutorialTitle = tutorial.getName(); holder.textViewName.setText(tutorialTitle); holder.textDescription.setText(tutorialDescription); if (holder.imageView != null) { /*-------------fatching image------------*/; new ImageDownloaderTask(holder.imageView).execute(imageUrl); } holder.imageView.setImageBitmap(bitmap); return convertView; } static class ViewHolder { TextView textViewName; TextView textDescription; ImageView imageView; } }

在build.gradle文件中添加以下库文件。
build.gradle

android { useLibrary 'org.apache.http.legacy' }dependencies { compile 'com.android.volley:volley:1.0.0' compile 'org.apache.httpcomponents:httpcore:4.4.1' compile 'org.apache.httpcomponents:httpclient:4.5' }

创建扩展AsyncTask < > 的匿名类ImageDownloaderTask.java。此类在执行doInbackground（）方法时从URL下载（或获取）图像，并将结果（位图）返回给onPostExecute（）。在onPostExecute（）方法中，位图设置为ImageView。
ImageDownloaderTask.java

package example.srcmini.com.volleyreadimagejson; import java.io.InputStream; import java.lang.ref.WeakReference; import java.net.HttpURLConnection; import java.net.URL; import org.apache.http.HttpStatus; import android.graphics.Bitmap; import android.graphics.BitmapFactory; import android.graphics.drawable.Drawable; import android.os.AsyncTask; import android.util.Log; import android.widget.ImageView; public class ImageDownloaderTask extends AsyncTask< String, Void, Bitmap> {private final WeakReference< ImageView> imageViewReference; public ImageDownloaderTask(ImageView imageView) { imageViewReference = new WeakReference< ImageView>(imageView); } @Override protected Bitmap doInBackground(String... params) { return downloadBitmap(params[0]); } @Override protected void onPostExecute(Bitmap bitmap) { if (isCancelled()) { bitmap = null; } if (imageViewReference != null) { ImageView imageView = imageViewReference.get(); if (imageView != null) { if (bitmap != null) { imageView.setImageBitmap(bitmap); } else { Drawable placeholder = imageView.getContext().getResources().getDrawable(R.drawable.placeholder); imageView.setImageDrawable(placeholder); } } } }private Bitmap downloadBitmap(String imageUrl) { HttpURLConnection urlConnection = null; try { URL uri = new URL(imageUrl); urlConnection = (HttpURLConnection) uri.openConnection(); int statusCode = urlConnection.getResponseCode(); if (statusCode != HttpStatus.SC_OK) { return null; } InputStream inputStream = urlConnection.getInputStream(); if (inputStream != null) { Bitmap bitmap = BitmapFactory.decodeStream(inputStream); return bitmap; } } catch (Exception e) { urlConnection.disconnect(); Log.w("ImageDownloader", "Error downloading image from " + imageUrl); } finally { if (urlConnection != null) { urlConnection.disconnect(); } } return null; } }

在MainActivity.java类中，我们使用Volley从URL中获取并解析JSON数据。
MainActivity.java

package example.srcmini.com.volleyreadimagejson; import android.support.v7.app.AppCompatActivity; import android.os.Bundle; import android.view.View; import android.widget.ListView; import android.widget.ProgressBar; import android.widget.Toast; import com.android.volley.Request; import com.android.volley.RequestQueue; import com.android.volley.Response; import com.android.volley.VolleyError; import com.android.volley.toolbox.StringRequest; import com.android.volley.toolbox.Volley; import org.json.JSONArray; import org.json.JSONException; import org.json.JSONObject; import java.util.ArrayList; import java.util.List; public class MainActivity extends AppCompatActivity {ListView listView; private static final String JSON_URL = "http://192.168.1.35:8080/jsondata/"; //the tutorial list where we will store all the tutorial objects after parsing json List< Tutorial> tutorialList; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); listView = (ListView) findViewById(R.id.listView); tutorialList = new ArrayList< >(); //this method will fetch and parse the data loadTutorialList(); }private void loadTutorialList() { //getting the progressbar final ProgressBar progressBar = (ProgressBar) findViewById(R.id.progressBar); progressBar.setVisibility(View.VISIBLE); //creating a string request to send request to the url StringRequest stringRequest = new StringRequest(Request.Method.GET, JSON_URL, new Response.Listener< String>() { @Override public void onResponse(String response) { //hiding the progressbar after completion progressBar.setVisibility(View.INVISIBLE); try { //getting the whole json object from the response JSONObject obj = new JSONObject(response); //we have the array named tutorial inside the object //so here we are getting that json array JSONArray tutorialsArray = obj.getJSONArray("tutorials"); //now looping through all the elements of the json array for (int i = 0; i < tutorialsArray.length(); i++) { //getting the json object of the particular index inside the array JSONObject tutorialsObject = tutorialsArray.getJSONObject(i); //creating a tutorial object and giving them the values from json object Tutorial tutorial = new Tutorial(tutorialsObject.getString("name"), tutorialsObject.getString("imageurl"), tutorialsObject.getString("description")); //adding the tutorial to tutoriallist tutorialList.add(tutorial); }//creating custom adapter object MyAdapter adapter = new MyAdapter(tutorialList, getApplicationContext()); //adding the adapter to listview listView.setAdapter(adapter); } catch (JSONException e) { e.printStackTrace(); } } }, new Response.ErrorListener() { @Override public void onErrorResponse(VolleyError error) { //displaying the error in toast if occur Toast.makeText(getApplicationContext(), error.getMessage(), Toast.LENGTH_SHORT).show(); } }); //creating a request queue RequestQueue requestQueue = Volley.newRequestQueue(this); //adding the string request to request queue requestQueue.add(stringRequest); } }

在AndroidManifest.xml中添加Internet权限
AndroidManifest.xml

< uses-permission android:name="android.permission.INTERNET" />

输出：

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