网络请求----HttpURLConnection的get，post和图片加载

URLConnection是个抽象类，它有两个直接子类分别是HttpURLConnection和JarURLConnection。另外一个重要的类是URL，通常URL可以通过传给构造器一个String类型的参数来生成一个指向特定地址的URL实例。

JDK自带的请求方式，包名: java.net.HttpURLConnection;

HttpURLConnection请求的类别:
分为二类,GET与POST请求。二者的区别在于：
1: get请求可以获取静态页面，也可以把参数放在URL字串后面，传递给servlet，

2: post与get的不同之处在于post的参数不是放在URL字串里面，而是放在http请求的正文内。

效果图：

代码：

public class Util {

/***
* get请求方式
* @param urlPath
* @return
*/
public static String get(String urlPath) {
HttpURLConnection conn = null; // 连接对象
InputStream is = null;
String resultData = "";
try {
URL url = new URL(urlPath); // URL对象
conn = (HttpURLConnection) url.openConnection(); // 使用URL打开一个链接
conn.setDoInput(true); // 允许输入流，即允许下载
conn.setDoOutput(true); // 允许输出流，即允许上传
conn.setUseCaches(false); // 不使用缓冲
conn.setRequestMethod("GET"); // 使用get请求
is = conn.getInputStream(); // 获取输入流，此时才真正建立链接
InputStreamReader isr = new InputStreamReader(is);
BufferedReader bufferReader = new BufferedReader(isr);
String inputLine = "";
while ((inputLine = bufferReader.readLine()) != null) {
resultData += inputLine + "\n";
}

} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
if (is != null) {
try {
is.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if (conn != null) {
conn.disconnect();
}
}
Log.i("get", resultData.toString());
return resultData;
}
/***
* post请求方式
* @param urlPath
* @param params
* @return
*/
public static String post(String urlPath, Map<String, String> params) {
if (params == null || params.size() == 0) {
return get(urlPath);
}
OutputStream os = null;
InputStream is = null;
HttpURLConnection connection = null;
StringBuffer body = getParamString(params);
byte[] data = body.toString().getBytes();
try {
URL url = new URL(urlPath);
// 获得URL对象
connection = (HttpURLConnection) url.openConnection();
// 获得HttpURLConnection对象
connection.setRequestMethod("POST");
// 设置请求方法为post
connection.setUseCaches(false);
// 不使用缓存
connection.setConnectTimeout(10000);
// 设置超时时间
connection.setReadTimeout(10000);
// 设置读取超时时间
connection.setDoInput(true);
// 设置是否从httpUrlConnection读入，默认情况下是true;
connection.setDoOutput(true);
// 设置为true后才能写入参数
connection.setRequestProperty("Content-Type",
"application/x-www-form-urlencoded");
connection.setRequestProperty("Content-Length",
String.valueOf(data.length));
os = connection.getOutputStream();
os.write(data);
// 写入参数
if (connection.getResponseCode() == HttpURLConnection.HTTP_OK) {
// 相应码是否为200
is = connection.getInputStream();
// 获得输入流
BufferedReader reader = new BufferedReader(
new InputStreamReader(is));
// 包装字节流为字符流
StringBuilder response = new StringBuilder();
String line;
while ((line = reader.readLine()) != null) {
response.append(line);
}
Log.i("post", response.toString());
return response.toString();
}
} catch (Exception e) {
e.printStackTrace();
} finally {
// 关闭
if (os != null) {
try {
os.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (is != null) {
try {
is.close();
} catch (IOException e) {
e.printStackTrace();
}
}
if (connection != null) {
connection.disconnect();
connection = null;
}
}
return null;
}

public static StringBuffer getParamString(Map<String, String> params) {
StringBuffer result = new StringBuffer();
Iterator<Map.Entry<String, String>> iterator = params.entrySet()
.iterator();
while (iterator.hasNext()) {
Map.Entry<String, String> param = iterator.next();
String key = param.getKey();
String value = param.getValue();
result.append(key).append('=').append(value);
if (iterator.hasNext()) {
result.append('&');
}
}
return result;
}

/**
*
* 图片加载
* @param url
* @return
*/
public static Bitmap getImageBitmap(String url) {
URL imgUrl = null;
Bitmap bitmap = null;
try {
imgUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection) imgUrl
.openConnection();
conn.setDoInput(true);
conn.connect();
InputStream is = conn.getInputStream();
bitmap = BitmapFactory.decodeStream(is);
is.close();
} catch (MalformedURLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return bitmap;
}

}

public class MainActivity extends Activity implements OnClickListener {
public static String urls = "http://bajie.zhangwoo.cn/app.php?platform=android&appkey=5a379b5eed8aaae531df5f60b12100cfb6dff2c1";

private TextView mTextView;
private ImageView imagegvoew;
String resultStr = "";
String resultStr1 = "";

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
}

private void initView() {
findViewById(R.id.btn1).setOnClickListener(this);
findViewById(R.id.btn2).setOnClickListener(this);
findViewById(R.id.btn3).setOnClickListener(this);
mTextView = (TextView) findViewById(R.id.Text);
imagegvoew = (ImageView) findViewById(R.id.imagegvoew);

}

@Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.btn1:
Thread visitBaiduThread = new Thread(new VisitWebRunnable());
visitBaiduThread.start();
try {
visitBaiduThread.join();
if (!resultStr.equals("")) {
mTextView.setText(resultStr);
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
case R.id.btn2:

Thread visitBaiduThreads = new Thread(new VisitWebRunnables());
visitBaiduThreads.start();
try {
visitBaiduThreads.join();
if (!resultStr1.equals("")) {
mTextView.setText(resultStr1);
}
} catch (InterruptedException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
break;
case R.id.btn3:
new Thread(new Runnable() {

@Override
public void run() {
// TODO Auto-generated method stub
new DownImgAsyncTask()
.execute("http://avatar.csdn.net/8/6/0/2_dickyqie.jpg");
}
}).start();

break;
default:
break;
}

}

class DownImgAsyncTask extends AsyncTask<String, Void, Bitmap> {

@Override
protected void onPreExecute() {
// TODO Auto-generated method stub
super.onPreExecute();

}

@Override
protected Bitmap doInBackground(String... params) {
// TODO Auto-generated method stub
Bitmap b = Util.getImageBitmap(params[0]);
return b;
}

@Override
protected void onPostExecute(Bitmap result) {
// TODO Auto-generated method stub
super.onPostExecute(result);
if (result != null) {
imagegvoew.setImageBitmap(result);
}
}

}

class VisitWebRunnable implements Runnable {

@Override
public void run() {
// TODO Auto-generated method stub
String data = Util.get(urls);
resultStr = data;
}

}

class VisitWebRunnables implements Runnable {

@Override
public void run() {
// TODO Auto-generated method stub
Map<String, String> params = new HashMap<String, String>();
params.put("q", "test");
params.put("showapi_appid", "11548");
params.put("showapi_timestamp", "20160511151954");
params.put("showapi_sign", "bb1d15ab7ce646ec87cc89d684ca4bcb");
String data = Util.post("https://route.showapi.com/32-9", params);
resultStr1 = data;
}

}
}

• 注意：使用时常出现出现NetworkOnMainThreadException错误，Android.os.NetworkOnMainThreadException错误提示的原因
• 原因：不允许在主线程中进行网络访问
• 解决：将网络访问的操作单独放到一个线程中

记得加网络权限

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

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