Android网络请求,数据解析及回调

单独依靠内置资源实现的App,在市场上不存在.通过用户的操作,向服务器发送请求,并将服务器返回的数据在App页面展现出来,是App运行的一般形式.App的正常运行就包括网络请求,数据解析,以及在同一线程执行任务时的回调.

两种网络请求:HttpURLConnectionOkHttp

Android向服务器发送请求的方式很多,总体分为两类,一个是内置的HttpURLConnection,另外是基于HttpURLConnection的开源框架.开源框架中又属Square公司开源的OkHttp应用范围最广.

连接网络首先需要申请权限,在AndroidManifest.xml中添加:

获取HttpUrlConnection,比较简单,通过URL的openConnection方法可以创建.

private void getByUrlConnection(){
        new Thread(new Runnable() {
            @Override
            public void run() {

                HttpURLConnection connection = null;
                BufferedReader reader = null;

                try{
                    URL url = new URL("https://www.baidu.com");
                    HttpURLConnection urlConnection = (HttpURLConnection)url.openConnection();
                    urlConnection.setConnectTimeout(8000);
                    urlConnection.setRequestMethod("GET");
                    urlConnection.setReadTimeout(8000);
                    InputStream inputStream = urlConnection.getInputStream();
                    reader = new BufferedReader((new InputStreamReader(inputStream)));
                    StringBuilder builder = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null){
                        builder.append(line);
                    }
                    showResponse(builder.toString());

                }catch (Exception e){
                    e.printStackTrace();
                }finally {
                    if (reader != null){
                        try{
                            reader.close();
                        }catch (IOException e){
                            e.printStackTrace();
                        }
                    }
                    if (connection != null){
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

private void showResponse(final String response){
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                textView.setText(response);
            }
        });
    }

用户使用App期间,出现卡顿会严重影响用户体验,消耗时间的网络请求需要放在子线程执行.

也可以使用OkHttp发送请求:

private void getByOkHttp(){
        new Thread(new Runnable() {
            @Override
            public void run() {
                OkHttpClient client = new OkHttpClient();
                Request request = new Request.Builder()
                        .url("http://www.baidu.com")
                        .get()
                        .build();
                try{
                    Response response = client.newCall(request).execute();
                    String responseData = response.body().string();
                    showResponse(responseData);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        }).start();

    }
数据请求中的两种形式:XML和Json

网络请求的数据需要按照一定的规则和协议,其中XML和Json两种数据形式,因为体积小,规则简单和实现方便得到了广泛的使用.

XML是Extensible Markup Language的简称,几乎可以在任何程序中进行数据交换.下面是一种简单的形式:


    
        1
        Chrome
        1.0
    
    
        2
        Safari
        1.0
    
    
        3
        FireFox
        1.0
    

Android对XML的解析方式有Pull和SAX两种.它们本质都是对文件按行读取,按照元素标记的开头和结尾来获取元素的内容.
Pull解析XML

private void pullXML(String data){
        try{
            XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
            XmlPullParser pullParser = factory.newPullParser();
            pullParser.setInput(new StringReader(data));
            int eventType = pullParser.getEventType();


            String id = "";
            String name = "";
            String version = "";
            while (eventType != XmlPullParser.END_DOCUMENT){

                String nodeName = pullParser.getName();
                switch (eventType){
                    case XmlPullParser.START_TAG:{
                        if ("id".equals(nodeName)){
                            id = pullParser.nextText();
                        }else if ("name".equals(nodeName)){
                            name = pullParser.nextText();
                        }else if ("version".equals(nodeName)){
                            version = pullParser.nextText();
                        }

                        break;
                    }
                    case XmlPullParser.END_TAG:{
                        if ("app".equals(nodeName)){
                            Log.e("END_TAG", "id = " + id);
                            Log.e("END_TAG", "name = " + name);
                            Log.e("END_TAG", "version = " + version);
                        }
                    }
                }
                eventType = pullParser.next();
            }
        }catch (Exception e){
            e.printStackTrace();
        }

    }

SAX解析XML

public class ContentHandler extends DefaultHandler {

    private String nodeName;
    private StringBuilder id;
    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 {
        
        Log.e("startElement", "startElement: " + uri + localName + qName + attributes.toString());
        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(localName)){
            Log.e("endElement", "id = " + id);
            Log.e("endElement", "name = " + name);
            Log.e("endElement", "version = " + version);

            id.setLength(0);
            name.setLength(0);
            version.setLength(0);
        }
    }

    @Override
    public void endDocument() throws SAXException {
        super.endDocument();
    }
}

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

Json是JavaScript Object Notation的简称,具有体积小,消耗流量少的特点,诞生于重视流量的移动端时代,二者的结合,让移动端更显流畅.Android系统包中自带了Json的的解析方式-JsonObject.Google开源的GSON解析Json也很方便.

JsonObject解析Json

private void parseJsonUseJsonObject(String data){
        try{
            JSONArray jsonArray = new JSONArray(data);
            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject jsObj =  jsonArray.getJSONObject(i);
                String id = jsObj.getString("id");
                String name = jsObj.getString("name");
                String version = jsObj.getString("version");
                Log.e("parseJsonUseJsonObject", "parseJsonUseJsonObject: " + id + name + version);
            }
        }catch (Exception e){
            e.printStackTrace();
        }
    }

GSON可以很方便地将Json格式的数据映射成对象,也即时MVC编程思想中的Model.
GSON解析Json

public class App {
    public String getId() {
        return id;
    }

    public void setId(String id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getVersion() {
        return version;
    }

    public void setVersion(String version) {
        this.version = version;
    }

    private String id;

    private String name;
    private String version;

}

private void parseJsonUseGson(String jsonData){
        Gson gson = new Gson();
        List appList = gson.fromJson(jsonData, new TypeToken>(){}.getType());
        for (App app: appList){
            Log.e("App", "id: " + app.getId());
            Log.e("App", "name: " + app.getName());
            Log.e("App", "version: " + app.getVersion());
        }
    }
数据回调

App为了提高运行效率和更好的用户体验,使用了多线程技术,可以同时处理多个任务.比如常常用到的网络请求,就是在子线程中执行.子线程中的执行结果,可以通过数据回调的方式顺利实现任务的按序执行.
实现数据回调,首先需要定义接口,然后在子线程中使用.

//定义接口
public interface HttpCallbackListener {
    void onFinish(String response);
    void onError(Exception e);
}
//使用
public static void SendHttpRequest(final String address, final HttpCallbackListener listener){
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                try{
                    URL url =  new URL(address);
                    connection = (HttpURLConnection)url.openConnection();
                    connection.setRequestMethod("GET");
                    connection.setConnectTimeout(8000);
                    connection.setReadTimeout(8000);

                    connection.setDoInput(true);
                    connection.setDoOutput(true);
                    InputStream in = connection.getInputStream();
                    BufferedReader reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null){
                        response.append(line);
                    }
                    if (listener != null){
                        listener.onFinish(response.toString());
                    }
                }catch (Exception e){
                    if (listener != null){
                        listener.onError(e);
                    }
                }finally {
                    if (connection != null){
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }
//调用
HttpUtil.SendHttpRequest("http://10.0.2.2/get_data.json", new HttpCallbackListener() {
    @Override
    public void onFinish(String response) {
        parseJson(response);
    }
    @Override
    public void onError(Exception e) {
    }
});
总结

网络相关的知识,可以用3个二和1个一来概括:
两种网络请求方式HttpURLConnection和OkHttp;
两种数据传递方式XML和Json,其中XML的解析用Pull和SAX,Json的解析用JsonObject和GSON;
一种数据回调,通过接口(Interface)来实现.

喜欢和关注都是对我的鼓励和支持~

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