Day1031

作业

单例模式饿汗式懒汉式 断点续传综合技能

单例模式

总体思路：先创建一个私有的private static 的对象，再创建一个私有的构造，防止外部调用修改；最后创建一个对外开放的静态的对象实例，返回值为return 对象； 饿汗式是先new出对象，等待调用；懒汉式是先创建对象为null，之后等待调用，只有当被调用时才会new出对象

饿汗式

//饿汗式 private static Utils utils = new Utils(); //私有构造 private Utils(){ } //提供对外公开的方法 public static Utils getInstance(){ return utils; }

懒汉式

需要上锁，双重校验锁，否则会造成线程安全问题

//懒汉式 private static Utils utils = null; //私有构造 private Utils(){ } //提供对外公开的方法 private static Utils getInstance(){ if (utils == null) { synchronized (Object.class){ if (utils == null) { utils = new Utils(); } } } return utils; }

断点续传

2次请求，第一次获取文件总长度，第二次获取从SD卡中获取的文件长度并继续用随机流下载

package com.example.work; import android.os.Handler; import android.os.Message; import android.util.Log; import java.io.File; import java.io.InputStream; import java.io.RandomAccessFile; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; public class MyThread extends Thread { private static final String TAG = "---"; private String path; private String str_url; private Handler handler; public MyThread(String path, String str_url, Handler handler) { this.path = path; this.str_url = str_url; this.handler = handler; } private long end; //总长度 private long start; //SD卡文件的长度 @Override public void run() { try { URL url = new URL(str_url); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); int responseCode = connection.getResponseCode(); Log.i(TAG, "code: "+responseCode); if (responseCode == 200) { end = connection.getContentLength(); } } catch (Exception e) { e.printStackTrace(); } File file = new File(path); if(file.exists()){ start = file.length(); }else{ start = 0; } try { URL url = new URL(str_url); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setRequestProperty("Range","bytes="+start+"-"+end); connection.connect(); int responseCode = connection.getResponseCode(); Log.i(TAG, "code: "+responseCode); Log.i(TAG, "run: "+start+" - "+end); if (responseCode == 206) { int len = 0; byte[] b = new byte[1024]; InputStream is = connection.getInputStream(); RandomAccessFile randomAccessFile = new RandomAccessFile(path,"rw"); randomAccessFile.seek(start); long count = start; while((len = is.read(b)) != -1){ randomAccessFile.write(b, 0, len); count += len; int values = (int) ((float)count/end*100); Message msg = Message.obtain(); msg.what = 0; msg.obj = values; Log.i(TAG, "values: "+values); handler.sendMessage(msg); } is.close(); } } catch (Exception e) { e.printStackTrace(); } } }

综合技能

package com.example.work; import android.Manifest; import android.app.ProgressDialog; import android.content.DialogInterface; import android.os.AsyncTask; import android.os.Bundle; import android.os.Environment; import android.os.Handler; import android.os.Message; import android.support.v7.app.AlertDialog; import android.support.v7.app.AppCompatActivity; import android.util.Log; import android.view.View; import android.view.ViewGroup; import android.widget.AdapterView; import android.widget.BaseAdapter; import android.widget.ImageView; import android.widget.ListView; import android.widget.TextView; import android.widget.Toast; import com.bumptech.glide.Glide; import com.google.gson.Gson; import java.io.ByteArrayOutputStream; import java.io.File; import java.io.FileOutputStream; import java.io.InputStream; import java.net.HttpURLConnection; import java.net.MalformedURLException; import java.net.URL; import java.util.ArrayList; import java.util.List; public class MainActivity extends AppCompatActivity { private ListView listView; private MyAdapter adapter; private String path2 = "http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1"; public static List<String> isLoad = new ArrayList<>(); private List<JavaBean.DataBean> dataList = new ArrayList<>(); public static List<String> name = new ArrayList<>(); private int index = 0; private ProgressDialog progressDialog; private File directory; private Handler handler = new Handler(){ @Override public void handleMessage(Message msg) { if (msg.what == 0) { isLoad.set(index,"已下载"); adapter.notifyDataSetChanged(); } else if (msg.what == 1) { progressDialog.setProgress((Integer) msg.obj); progressDialog.dismiss(); if((Integer) msg.obj == 100){ Toast.makeText(MainActivity.this, "下载成功！", Toast.LENGTH_SHORT).show(); } } else if (msg.what == 2) { Toast.makeText(MainActivity.this, "已经下载过了", Toast.LENGTH_SHORT).show(); progressDialog.dismiss(); } } }; private long start = 0; private long end = 0; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); requestPermissions(new String[]{Manifest.permission.WRITE_EXTERNAL_STORAGE, Manifest.permission.READ_EXTERNAL_STORAGE}, 1000); initView(); } private void initView() { listView = (ListView) findViewById(R.id.list_view); adapter = new MyAdapter(dataList,MainActivity.this); listView.setAdapter(adapter); new MyAsyncTask(dataList,adapter).execute(path2); listListener(); } private void listListener() { listView.setOnItemClickListener(new AdapterView.OnItemClickListener() { @Override public void onItemClick(AdapterView<?> parent, View view, final int position, long id) { MyDialog(position); } }); } private void MyDialog(final int position) { AlertDialog.Builder builder = new AlertDialog.Builder(MainActivity.this); builder.setMessage("是否下载？"); builder.setTitle("提示信息"); builder.setPositiveButton("确定", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { progressDialog = new ProgressDialog(MainActivity.this); progressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL); progressDialog.setMessage("下载中。。。"); index = position; new Thread(new Runnable() { @Override public void run() { try { URL url = new URL(dataList.get(position).getPic()); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); if (connection.getResponseCode() == 200) { end = connection.getContentLength(); } } catch (Exception e) { e.printStackTrace(); } directory = Environment.getExternalStorageDirectory(); File file = new File(directory, name.get(position)); if (file.exists()) { start = file.length(); }else{ start = 0; } if(start == end){ handler.sendEmptyMessage(2); return; } try { URL url = new URL(dataList.get(position).getPic()); HttpURLConnection connection = (HttpURLConnection) url.openConnection(); connection.setRequestProperty("Range","bytes="+start+"-"+end); connection.connect(); if (connection.getResponseCode() == 206) { int len = 0; byte[] b = new byte[1024]; InputStream is = connection.getInputStream(); FileOutputStream fos = new FileOutputStream(new File(directory,name.get(position))); long count = start; while ((len = is.read(b)) != -1) { // Thread.sleep(1000); fos.write(b, 0, len); count += len; int values = (int) ((float)count/end*100); Message obtain = Message.obtain(); obtain.what = 1; obtain.obj = values; handler.sendMessage(obtain); } handler.sendEmptyMessage(0); connection.disconnect(); is.close(); fos.close(); } } catch (Exception e) { e.printStackTrace(); } } }).start(); progressDialog.show(); } }); builder.setNegativeButton("取消", new DialogInterface.OnClickListener() { @Override public void onClick(DialogInterface dialog, int which) { } }); AlertDialog alertDialog = builder.create(); alertDialog.show(); } }