@[toc] 断点续传 和 单例
断点续传
activity
package com
.example
.day01_homework
;
import android
.Manifest
;
import android
.content
.DialogInterface
;
import android
.os
.Build
;
import android
.os
.Handler
;
import android
.os
.Message
;
import android
.support
.v7
.app
.AlertDialog
;
import android
.support
.v7
.app
.AppCompatActivity
;
import android
.os
.Bundle
;
import android
.view
.View
;
import android
.widget
.AdapterView
;
import android
.widget
.ImageView
;
import android
.widget
.ListView
;
import android
.widget
.ProgressBar
;
import android
.widget
.Toast
;
import java
.io
.File
;
import java
.util
.ArrayList
;
import java
.util
.List
;
public class MainActivity extends AppCompatActivity {
private ListView listView
;
private ProgressBar progressList
;
private MyAdapter adapter
;
private String path
= "http://www.qubaobei.com/ios/cf/dish_list.php?stage_id=1&limit=20&page=1";
private List
<Food.DataBean> list
= new ArrayList<>();
private String url
= "/storage/emulated/0/Pictures/";
public static long all
= 0;
private String path1
= "";
private Handler handler
= new Handler() {
@Override
public void handleMessage(Message msg
) {
super.handleMessage(msg
);
if (msg
.what
== 120) {
int len
= (int) msg
.obj
;
progressList
.setProgress(len
);
if (len
== 100) {
progressList
.setVisibility(View
.GONE
);
Toast
.makeText(MainActivity
.this, "下载完成", Toast
.LENGTH_SHORT
).show();
}
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState
) {
super.onCreate(savedInstanceState
);
setContentView(R
.layout
.activity_main
);
if (Build
.VERSION
.SDK_INT
>= Build
.VERSION_CODES
.M
) {
requestPermissions(new String[]{Manifest
.permission
.WRITE_EXTERNAL_STORAGE
, Manifest
.permission
.READ_EXTERNAL_STORAGE
}, 110);
}
initview();
loadFromNet();
}
private void loadFromNet() {
new MyAsynctask(list
, adapter
).execute(path
);
}
private void initview() {
listView
= (ListView
) findViewById(R
.id
.list_view
);
progressList
= (ProgressBar
) findViewById(R
.id
.progress_list
);
adapter
= new MyAdapter(list
, this);
listView
.setAdapter(adapter
);
listView
.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView
<?> parent
, View view
, final int position
, long id
) {
path1
= url
+ position
+ ".jpg";
File file
= new File(path1
);
if (file
.exists()) {
Toast
.makeText(MainActivity
.this, "图片已存在", Toast
.LENGTH_SHORT
).show();
} else {
Toast
.makeText(MainActivity
.this, "图片不存在", Toast
.LENGTH_SHORT
).show();
AlertDialog
.Builder builder
= new AlertDialog.Builder(MainActivity
.this);
builder
.setTitle("友情提示！");
builder
.setMessage("是否下载该图片");
builder
.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog
, int which
) {
}
});
builder
.setPositiveButton("Allow", new DialogInterface.OnClickListener() {
@Override
public void onClick(DialogInterface dialog
, int which
) {
progressList
.setVisibility(View
.VISIBLE
);
String pic
= list
.get(position
).getPic();
new MyThread(pic
, path1
, handler
).start();
}
});
AlertDialog dialog
= builder
.create();
dialog
.show();
}
}
});
}
}
子线程
package com
.example
.day01_homework
;
import android
.os
.Handler
;
import android
.os
.Message
;
import android
.util
.Log
;
import java
.io
.File
;
import java
.io
.IOException
;
import java
.io
.InputStream
;
import java
.io
.RandomAccessFile
;
import java
.net
.HttpURLConnection
;
import java
.net
.MalformedURLException
;
import java
.net
.URL
;
class MyThread extends Thread {
private String str_url
;
private String path
;
private Handler handler
;
public MyThread(String str_url
, String path
, Handler handler
) {
this.str_url
= str_url
;
this.path
= path
;
this.handler
= handler
;
}
private long end
;
private long start
;
@Override
public void run() {
super.run();
try {
URL url
= new URL(str_url
);
HttpURLConnection connection
= (HttpURLConnection
) url
.openConnection();
connection
.setReadTimeout(3 * 1000);
connection
.setConnectTimeout(3 * 1000);
connection
.connect();
if (connection
.getResponseCode() == 200) {
end
= connection
.getContentLength();
Log
.d("TAG", "end: " + end
);
}
} catch (MalformedURLException e
) {
e
.printStackTrace();
} catch (IOException e
) {
e
.printStackTrace();
}
File file
= new File(path
);
if (file
.exists()) {
start
= file
.length();
} else {
start
= 0;
}
Log
.d("TAG", "start: " + start
);
try {
URL url
= new URL(str_url
);
HttpURLConnection connection
= (HttpURLConnection
) url
.openConnection();
connection
.setReadTimeout(3 * 1000);
connection
.setConnectTimeout(3 * 1000);
connection
.setRequestProperty("Range", "bytes=" + start
+ "-" + end
);
connection
.connect();
if (connection
.getResponseCode() == 206) {
InputStream inputStream
= connection
.getInputStream();
RandomAccessFile randomAccessFile
= new RandomAccessFile(path
, "rw");
randomAccessFile
.seek(start
);
int len
= 0;
byte[] bytes
= new byte[1024];
long count
= start
;
while ((len
= inputStream
.read(bytes
)) != -1) {
randomAccessFile
.write(bytes
, 0, len
);
count
+= len
;
int progress
= (int) ((count
* 100) / end
);
Log
.d("TAG", "run: " + progress
);
Message obtain
= Message
.obtain();
obtain
.what
= 120;
obtain
.obj
= progress
;
handler
.sendMessage(obtain
);
}
}
} catch (MalformedURLException e
) {
e
.printStackTrace();
} catch (IOException e
) {
e
.printStackTrace();
}
}
}
单例 懒汉
package com
.example
.day01_homework
;
public class TestUtils2 {
private TestUtils2() {
}
private static TestUtils2 testUtils2
= null
;
public static TestUtils2
getInstance() {
if (testUtils2
== null
) {
synchronized (Object
.class) {
if (testUtils2
== null
) {
testUtils2
= new TestUtils2();
}
}
}
return testUtils2
;
}
}
package com
.example
.day01_homework
;
public class Teest02 {
public void test() {
TestUtils2 instance1
= TestUtils2
.getInstance();
TestUtils2 instance2
= TestUtils2
.getInstance();
if (instance1
.equals(instance2
)) {
System
.out
.println("1346789");
} else {
System
.out
.println("987654321");
}
}
}
饿汉
package com
.example
.day01_homework
;
public class TestUtils {
private TestUtils() {
}
private static TestUtils testUtils
= new TestUtils();
public static TestUtils
getInstance() {
return testUtils
;
}
}
package com
.example
.day01_homework
;
public class single_e {
public void getTest() {
TestUtils utils1
= TestUtils
.getInstance();
TestUtils utils2
= TestUtils
.getInstance();
if (utils1
.equals(utils2
)) {
System
.out
.println("1346789");
} else {
System
.out
.println("987654321");
}
}
}
总结
断点续传 就是在下载的过程中给数据加上一个标记，就是从本地的缓存中读取已下载的部分，然后在网络请求中加上一个请求头，来从服务端请求数据，只请求未下载的部分。
单例 懒汉 懒汉式就是在开始的时候不去创建对象，而是在后面进行创建，但是这个会有线程安全的问题，在这里就需要用到双重校验锁，就是一个同步锁里面嵌套一个判断，判断对象是否已存在，如果已存在就复用。
而饿汉就是在一开始就创建出对象，这样就不会产生线程安全问题，但是这样会比较下号资源。
