Android Studio —— Web技术

第一行代码读书笔记

WebView

• 在应用程序里嵌入一个浏览器

WebView webView = (WebView) findViewById(R.id.web_view);
// 设置浏览器属性
webView.getSettings().setJavaScriptEnabled(true);
// 当需要从一个网页跳转到另一个网页时，目标网页仍在当前WebView中显示
webView.setWebViewClient(new WebViewClient());
webView.loadUrl("http://www.baidu.com");

• 权限声明
  <uses-permission android:name="android:permission:INTERNET" />

使用HTTP协议访问网络

HttpURLConnection

// 获取HttpURLConnection实例
URL url = new URL("http://www.baidu.com");
HttpURLConnection connection = (HttpURLConnection) url.openConnection();

// 设置HTTP请求所使用的方法
// GET/POST
connection.setRequestMethod("GET");

//自定义设置
connection.setConnectTimeout(8000);
connection.setReadTimeout(8000);

// 获取服务器返回的输入流
InputStream in = connection.getInputStream();

// 关闭HTTP连接
connection.disconnect();

• 开启子线程发起HTTP请求，用runOnUiThread()方法将线程切换到主线程进行UI操作
• POST：在获取输入流之前把要提交的数据写出，每条数据都要以键对值的形式存在，数据与数据之间用&符号隔开

  connection.setRequestMethod("POST");
  DataOutputStream out = new DataOutputStream(connection.getOutputStream());
  out.writeByte("username=admin&password=123456");
  

OkHttp

• 项目地址：https://github.com/square/okhttp
• 添加依赖 'com.sqareup.okhttp3:okhttp:3.4.1'
• GET

  // 创建OkHttpClient
  OkHttpClient client = new OkHttpClient();
  // 创建空的Request对象
  // Request request = new Request.Builder().build();
  // 在最终的build()之前连缀其他方法丰富Request对象
  Request request = new Request.Builder().url("www.baidu.com").build();
  
  // 创建Call对象，并调用它的execute()放松请求并获取服务器返回的数据
  // Response对象就是服务器返回的数据
  Response response = client.newCall(request).execute();
  // 获取返回的具体内容
  String responseData = response.body().string();
  

• POST

  // 创建OkHttpClient
  OkHttpClient client = new OkHttpClient();
  // 构建一个RequestBody对象存放待提交的数据
  RequestBody requestBody = new FormBody.Builder
          .add("username", "admin")
          .add("password", "123456")
          .build()
  // 在Request.Builder中调用post()方法，并将RequestBody对象传入
  Request request = new Request.Builder()
          .url("www.baidu.com")
          .post(requestBody)
          .build();
  
  // 创建Call对象，并调用它的execute()放松请求并获取服务器返回的数据
  // Response对象就是服务器返回的数据
  Response response = client.newCall(request).execute();
  

解析XML格式数据

Pull解析

private void parseXMLWithPull(String xmlData) {
    try {
        XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
        XmlPullParser xmlPullParser = factory.newPullParser();
        xmlPullParser.setInput(new StringReader(xmlData));
        int eventType = xmlPullParser.getEventType();
        String id = "";
        String name = "";
        String version = "";
        while (eventType != XmlPullParser.END_DOCUMENT) {
            String nodeName = xmlPullParser.getName();
            switch (eventType) {
                case XmlPullParser.START_TAG: {
                    if ("id".equals(nodeName)) {
                        id = xmlPuallParser.nextText();
                    } else if ("name".equals(nodeName)) {
                        name = xmlPuallParser.nextText();
                    } else if ("version".equals(nodeName)) {
                        version = xmlPuallParser.nextText();
                    }
                    break;
                }
                
                case XmlPuallParser,END_TAG: {
                    if ("app".equals(nodeName)) {
                        Log.d("MainActivity", "id is " + id);
                        Log.d("MainActivity", "name is " + name);
                        Log.d("MainActivity", "version is " + version);
                    }
                    break;
                }
                default:
                    break;
            }
            eventType = xmlPuallParser.next();
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

SAX解析

• 用法比Pull解析复杂一些，语义方面更清楚

public class MyHandler extends DefaultHandler {

    private String nodeName;
    
    private StringBuilderid;
    
    private StringBuilder name;
    
    private StringBuilder version;

    @Override
    public void startDocument() throws SAXException {
        id = new StringBuilder();
        name = new StringBuilder();
        version = new StringBuilder();
    }
    
    @Override
    public void startElement(String uri, String localName, String qName, Attributes attributes) throws SAXException {
        nodeName = localName;
    }
    
    @Override
    public void characters(char[] ch, int start, int length) throws SAXException {
        if ("id".equals(nodeName)) {
            id.append(ch, start, length);
        } else if ("name".equals(nodeName)) {
            name.append(ch, start, length);
        } else if ("version".equals(nodeName)) {
            version.append(ch, start, length);
        }
    }
    
    @Override
    public void endElement(String uri, String localName, String qName) throws SAXException {
        if ("app".equals(nodeName)) {
            Log.d("ContentHanlder", "id is " + id.toString().trim());
            Log.d("ContentHanlder", "name is " + name.toString().trim());
            Log.d("ContentHanlder", "version is " + version.toString().trim());
            id.setLength(0);
            name.setLength(0);
            version.setLength(0);
        }
    }
    
    @Override
    public void endDocument() throws SAXException {
        super.endDocument();
    }
}

• startDocument() startElement() characters() endElement() endDocument()

private void parseXMLWithSAX(String xmlData) {
    try {
        SAXParserFactory factory = SAXParserFactory().newInstance();
        XMLReader xmlReader = factory.newSAXParser().getXMLReader();
        ContentHandler handler = new ContentHandler();
        xmlReader.setContentHandler(handler);
        xmlReader.parse(new InputSource(new StringReader(XmlData)));
    } catch (Exception e) {
        e.printStackTrace();
    }
}

DOM解析

• 略

解析JSON格式数据

• JSONObject, GSON, Jackson, FastJSON etc.

JSONObject

• 官方提供

private void parseJSONObject(String jsonData) {
    try {
        JSONArray jsonArray = new JSONArray(jsonData);
        for (int i = 0; i < jsonArray.length(); i++) {
            JSONObject jsonObject = jsonArray.getJSONObject(i);
            String id = jsonObject.getString("id");
            String name = jsonObject.getString("name");
            String version = jsonObject.getString("version");
            Log.d("MainActivity", "id is " + id);
            Log.d("MainActivity", "name is " + name);
            Log.d("MainActivity", "version is " + version);
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

GSON

• 添加依赖
  'com.google.code.gson:gson:2.7'
• 解析一个到类

  Gson gson = new Gson();
  Person person = gson.fromJson(jsonData, Person.class);
  

• 解析一段

  List<App> appList = gson.fromJson(jsonData, new TypeToken<List<App>>(){}.getType());
  

private void parseJSONWithGSON(String jsonData) {
    Gson gson = new Gson();
    List<App> appList = gson.fromJson(jsonData, new TypeToken<List<App>>(){}.getType());
    for (App app : appList) {
        Log.d("MainActivity", "id is " + id);
        Log.d("MainActivity", "name is " + name);
        Log.d("MainActivity", "version is " + version);
    }
}