Java代码片段

// 《Android进阶之光》p214
public class Main {
    private static String convertStreamToString(InputStream stream) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(stream));
        StringBuffer sb = new StringBuffer();
        String line;
        while ((line = reader.readLine()) != null) {
            sb.append(line).append("\n");
        }
        String response = sb.toString();
        return response;
    }

    // https://stackoverflow.com/questions/43157/easy-way-to-write-contents-of-a-java-inputstream-to-an-outputstream
    // http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/IOUtils.html
    // http://commons.apache.org/proper/commons-io/download_io.cgi
    public static void convertStreamToFile(InputStream in, File out) throws IOException {
        FileOutputStream outStream = new FileOutputStream(out);
        IOUtils.copy(in, outStream);
        in.close();
        outStream.close();
    }

    public static void main(String[] args) {
        // 网络图片
        InputStream stream = new URL("https://www.cnblogs.com/images/logo_small.gif").openStream();

        convertStreamToFile(stream, new File("./java/cnblog_logo.png"));

        // 网页
        InputStream stream2 = new URL("https://www.cnblogs.com/").openStream();

        convertStreamToFile(stream2, new File("./java/cnblog.html"));

        // 本地文件
        FileInputStream fileInputStream = new FileInputStream("./java/hi.txt");

        convertStreamToFile(fileInputStream, new File("./java/hi2.txt"));

        // 获取字符串
        FileInputStream fileInputStream2 = new FileInputStream("./java/hi.txt");
        String str = convertStreamToString(fileInputStream2);
        System.out.println(str);
    }
}

定时功能

ScheduledExecutorService service = Executors.newScheduledThreadPool(1);
service.schedule(new Runnable() {
    @Override
    public void run() {
        System.out.println("Yeah, I'm late.");
        service.shutdown();
    }
}, 10, TimeUnit.SECONDS);

多线程调试

一次只打一个断点。

获取服务器时间

原理：通过获取链接的 Header 信息来获取时间。
注意：网络请求需要在多线程中执行

URL url = new URL("http://lyloou.com");
URLConnection uc = url.openConnection();// 获取连接对象
uc.connect();// 连接
long webTimeMillis = uc.getDate();
SimpleDateFormat simpleDateFormat = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss", Locale.CHINA);
String formatWebTime = simpleDateFormat.format(new Date(webTimeMillis));
System.out.println(formatWebTime);

添加顺序的注释

参考资料:深入探索 Android 热修复技术原理 7.3Q.pdf p107

// %% Part 1. 创建了新对象；
// %% Part 2. 找到旧对象的引用；
// %% Part 3. 用新对象赋值给旧对象的引用；

对象转换成字符串

在不确定对象是否为空时，通过String.valueOf(object)的方法，
而不是直接调用：object.toString();方法

封装

当类似的代码多次出现的时候，就可以考虑将其封装起来。

日期、时间格式的转换

• GankBeautyResultToItemsMapper.java

String strDate = "2017-05-09T14:28:32.974Z";
SimpleDateFormat inputFormat = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss.SS'Z'");
SimpleDateFormat outputFormat = new SimpleDateFormat("yy/MM/dd HH:mm:ss");
try {
    Date inputDate = inputFormat.parse(strDate);
    String outputDate = outputFormat.format(inputDate);
    System.out.println(outputDate);
} catch (ParseException e) {
    e.printStackTrace();
}

打印出好看的list

System.out.println(Arrays.toString(list.toArray()));

HashMap 用来缓存对象

private static final Map<String, Object> objectsCache = new HashMap<>();

// put in
public void putIn(String key, Object obj) {
  objectsCache.put(key, obj);
}

// get out
public Object getOut(String key, Object default) {
  if(objectsCache.containsKey(key)) {
    Object obj = objectsCache.get(key);
    if(obj == null) {
      objectsCache.put(key, default);
    }
    return obj;
  } else {
    objectsCache.put(key, default);
    return default;
  }
}

根据 class 将 object 对象转换成 class 的对象

MyClass mobj = MyClass.class.cast(obj);
// or
Object newObj = Class.forName(classname).cast(obj);