接口回调
在对象中，有些事件不确定什么时候能完成，此时可以通过预留监督机制，关注事件的变化，这个机制即回调。
举个例子
模拟下载，实施监督下载的进度，当100%时，提醒下载完成
1. 建立一个下载进度的类
需要监督加载的进度，因此方法内需要一个监督进度的形参接口
class Progress {
public void loadProgress(IProgressListener progressListener) {
//模拟进度
for (int i = 1; i <= 100; i++) {
//进度每改变一次，即调用更新一次监督的数据
progressListener.curProgress(i);
}
}
}
2. 建立监听的回调接口，用来监听进度
interface IProgressListener {
void curProgress(int curProgress);
}
3.运行调用
实际还是对多态的运用
当Progress类调用loadProgress(IProgressListener progressListener)时
传入的实参是一个匿名内部类，也是IProgressListener的子类
相当于 IProgressListener progressListener = new 子类();
此时调用的是子类的实现。
public class Main {
public static void main(String[] args) {
Progress progress = new Progress();
progress.loadProgress(new IProgressListener() {
@Override
public void curProgress(int curProgress) {
System.out.printf("curProgress：" + curProgress + "\r\n");
if (curProgress == 100)
System.out.printf("下载完成");
}
});
}
}
OkHttp
Android网络请求的变迁
OkHttp的基本用法
前置工作
1. 添加依赖
OkHttp依赖：implementation 'com.squareup.okhttp3:okhttp:3.11.0'
Gson依赖：implementation 'com.google.code.gson:gson:2.8.5'
2. Android在做网络请求时要添加权限
注意
Android P 限制了明文流量的网络请求，非加密的流量请求都会被系统禁止。
如果 WebView 的 url 用 http 协议，同样会出现加载失败，https 不受影响。
如果当前应用的请求是 htttp 而非 https，系统会禁止当前应用进行该请求。
在 Android P 版本如果使用了明文流量，OkHttp3会抛出
CLEARTEXT communication to " + host + " not permitted by network security policy异常
解决方案
服务器和客户端的请求最好都用https
OkHttp提供的API
Get请求
1. 首先创建OkHttpClient
OkHttpClient okHttpClient = new OkHttpClient();
2. 发送请求需要构建Request对象
Request request = new Request.Builder()
.url(requestUrl())
.build();
3. okHttpClient 调用newCall()创建一个Call对象，并调用enqueue()
发送请求并获取服务器返回的数据。
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
if (response.isSuccessful()) {
String resJson = response.body().string();
Gson gson = new Gson();
User user = gson.fromJson(resJson, User.class);
}
}
});
Post请求
1. 需要构建一个RequestBody对象来存放提交的参数
RequestBody body = new FormBody.Builder()
.add("userName", getUserName())
.add("userCode", getUserCode())
.build();
2. 将body 添加到Request.Builder中
Request request = new Request.Builder()
.url(requestUrl())
.post(body)
.build();
举个例子
客户端向服务器发送用户输入的用户名，用户编号
服务端返回用户的信息
1. 服务端
Module类
public class User {
String name;
int code;
String info;
}
@WebServlet(value = "/user")
public class UserServlet extends HttpServlet {
@Override
protected void service(HttpServletRequest req, HttpServletResponse resp)
throws ServletException, IOException {
req.setCharacterEncoding("UTF-8");
resp.setContentType("text/html;charset=UTF-8");
Gson gson = new Gson();
String userName = req.getParameter("userName");
String userCode = req.getParameter("userCode");
if (userName.equals("admin") && userCode.equals("123")) {
User user = new User("admin", 1, "演示信息");
resp.getWriter().println(gson.toJson(user));
}
}
}
2. 客户端
public class MainActivity extends AppCompatActivity {
private static final String TAG = "MainActivity";
private EditText mEtUserName;
private EditText mEtUserCode;
private Button mBtnQuery;
private TextView mTvShowUserInfo;
@SuppressLint("HandlerLeak")
private Handler mHandler = new Handler() {
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case 1:
User user = (User) msg.obj;
showUserInfo(user);
break;
}
}
};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
initView();
initEvent();
}
private void initEvent() {
mBtnQuery.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
getUserInfo();
}
});
}
//网络请求
private void getUserInfo() {
OkHttpClient okHttpClient = new OkHttpClient();
RequestBody body = new FormBody.Builder()
.add("userName", getUserName())
.add("userCode", getUserCode())
.build();
final Request request = new Request.Builder()
.url(requestUrl())
.post(body)
.build();
okHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
}
@Override
public void onResponse(Call call, Response response) throws IOException {
if (response.isSuccessful()) {
String resJson = response.body().string();
Gson gson = new Gson();
User user = gson.fromJson(resJson, User.class);
Message message = Message.obtain();
message.what = 1;
message.obj = user;
mHandler.sendMessage(message);
}
}
});
}
private void initView() {
mEtUserName = findViewById(R.id.et_user_name);
mEtUserCode = findViewById(R.id.et_user_code);
mBtnQuery = findViewById(R.id.btn_query_data);
mTvShowUserInfo = findViewById(R.id.tv_user_info_show);
}
private String getUserName() {
return mEtUserName.getText().toString();
}
private String getUserCode() {
return mEtUserCode.getText().toString();
}
private void showUserInfo(User user) {
StringBuilder builder = new StringBuilder();
builder.append("UserName：" + user.getName())
.append("\r\n")
.append("UserCode：" + user.getCode())
.append("\r\n")
.append("UserInfo：" + user.getInfo());
mTvShowUserInfo.setText(builder.toString());
}
private String requestUrl() {
return "http://192.168.1.104:8080/user";
}
}
OkHttp封装
思路
通过观察OkHttp，不难发现所有的请求都是通过Request这个类构建
为了保证不浪费资源，将OkHttp设置为单例模式。
1. 用枚举区分Get，Post，设置对外调用方法，获取网络请求
传递参数
1.请求的路径
2.post请求时传递的参数
3.一个用于监测请求完成的回调类
2. 定义OkHttp的请求doRequest()方法，用于监听请求成功失败，请求前的状态
传递参数
1.构建的Request类
2.监听回调类
3. 所有请求都用异步在子线程操作，修改UI需要Handler发送到主线程
这就需要根据成功失败的回调，创建发送的Handler方法
4. 定义回调类
1.请求成功
2.请求失败
5. 设置回调的包装类，帮助简化构建不必要的方法
1. 设置回调类
public abstract class IBaseCallBack {
public Type mType;
public IBaseCallBack() {
mType = getSuperclassTypeParameter(getClass());
}
/**
* 将Type类型转换成Gson，解析
*/
static Type getSuperclassTypeParameter(Class subclass) {
Type superclass = subclass.getGenericSuperclass();
if (superclass instanceof Class) {
throw new RuntimeException("Missing type parameter.");
}
ParameterizedType parameterized = (ParameterizedType) superclass;
return $Gson$Types.canonicalize(parameterized.getActualTypeArguments()[0]);
}
//请求成功前回调
public abstract void onRequestBefore();
//网络请求成功后根据返回码调用
public abstract void onSuccess(Response response, T t);
//请求失败时
public abstract void onFailure(Call call, Exception e);
}
2. 将OkHttp封装
public class OkHttpHelper {
private static OkHttpHelper mOkHttpHelper;
private static OkHttpClient mOkHttpClient;
private static Gson mGson;
private Handler mHandler;
private OkHttpHelper() {
mOkHttpClient = new OkHttpClient();
mGson = new Gson();
//每发现一条消息就推送到Handler
mHandler = new Handler(Looper.getMainLooper());
}
public static OkHttpHelper getOkHttpHelperInstance() {
if (mOkHttpHelper == null) {
synchronized (OkHttpHelper.class) {
if (mOkHttpHelper == null) {
mOkHttpHelper = new OkHttpHelper();
}
}
}
return mOkHttpHelper;
}
//来区别请求的类型
enum HttpMethodType {
GET, POST
}
/**
* 对外调用的Get，Post请求
*/
public void get(String url, IBaseCallBack callBack) {
Request request = buildRequest(
url,
null,
HttpMethodType.GET);
doRequest(request, callBack);
}
public void post(String url, Map parameter,
IBaseCallBack callBack) {
Request request = buildRequest(
url,
parameter,
HttpMethodType.POST);
doRequest(request, callBack);
}
/**
* 构建Get或Post请求的Request
*
* @param url Url地址
* @param parameter Post请求所需要的参数
* @param methodType 通过枚举来判断是Get还是Post
* @return Request
*/
private Request buildRequest(String url,
Map parameter,
HttpMethodType methodType) {
Request.Builder builder = new Request.Builder();
builder.url(url);
if (methodType == HttpMethodType.GET) {
builder.get();
} else {
//构建参数获取
RequestBody body = buildFormData(parameter);
builder.post(body);
}
return builder.build();
}
/**
* 构建Post请求的body
*/
private RequestBody buildFormData(Map parameter) {
FormBody.Builder body = new FormBody.Builder();
if (null != parameter) {
for (Map.Entry entry : parameter.entrySet()) {
body.add(entry.getKey(), entry.getValue());
}
}
return body.build();
}
/**
* 通过构建好的Get或Post请求的Request，做网络访问
*/
private void doRequest(final Request request, final IBaseCallBack callBack) {
callBack.onRequestBefore();
mOkHttpClient.newCall(request).enqueue(new Callback() {
@Override
public void onFailure(Call call, IOException e) {
requestFailure(callBack, call, e);
}
@Override
public void onResponse(Call call, Response response)
throws IOException {
if (response.isSuccessful()) {
String resultStr = response.body().string();
if (callBack.mType == String.class) {
requestSuccess(callBack, response, request);
} else {
try {
//防止Json解析错误
Object obj = mGson.fromJson(resultStr, callBack.mType);
requestSuccess(callBack, response, obj);
} catch (JsonParseException e) {
requestFailure(callBack, call, e);
}
}
} else {
requestFailure(callBack, call, null);
}
}
});
}
private void requestFailure(final IBaseCallBack callBack,
final Call call,
final Exception e) {
mHandler.post(new Runnable() {
@Override
public void run() {
callBack.onFailure(call, e);
}
});
}
private void requestSuccess(final IBaseCallBack callBack,
final Response response,
final Object o) {
mHandler.post(new Runnable() {
@Override
public void run() {
callBack.onSuccess(response, o);
}
});
}
}
3. 设置接口的包装类，帮助简化不必要的实现接口或者添加其他方法
注意：两者同样是抽象类，SpotsCallBack重写的抽象方法，在其子类是不会主动提示覆盖的
public abstract class SpotsCallBack extends IBaseCallBack {
ProgressDialog mDialog;
public SpotsCallBack(Context context) {
mDialog = new ProgressDialog(context);
mDialog.setCancelable(false);
mDialog.setCanceledOnTouchOutside(false);
}
public void showDialog() {
mDialog.show();
}
public void dismissDialog() {
mDialog.dismiss();
}
@Override
public void onRequestBefore() {
showDialog();
}
}
具体调用
private void getUserInfo() {
HashMap paramester = new HashMap<>();
paramester.put("userName", getUserName());
paramester.put("userCode", getUserCode());
OkHttpHelper.getOkHttpHelperInstance()
.post(requestUrl(), paramester, new SpotsCallBack(this) {
@Override
public void onSuccess(Response response, User user) {
dismissDialog();
showUserInfo(user);
}
@Override
public void onFailure(Call call, Exception e) {
dismissDialog();
}
});
}