使用HTTP协议访问网络

一.使用HttpURLConnection

①首先获取HttpURLConnection的实例

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

②在得到HttpURLConnection的实例后，可以设置HTTP请求所使用的方法。常用的方法主要有两个：GET和POST。GET表示从服务器那里获取数据，POST则是将数据提交给服务器。

connection.setRequestMethod("GET");

③自由定制

// 设置是否使用缓存
connection.setUseCaches(true);
// 设置此 HttpURLConnection 实例是否应该自动执行 HTTP 重定向
connection.setInstanceFollowRedirects(true);
// 设置超时时间
connection.setConnectTimeout(3000);

④利用getInputStream()方法获取输入流，然后读取

InputStream in =connection.getInputStream();

⑤关闭HTTP连接

if(connection != null){
    connection.disconnect();
}

⑥完整Activity代码

package com.example.administrator.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import java.io.BufferedReader;
import java.io.DataOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;

public class HttpActivity extends AppCompatActivity implements View.OnClickListener {
    TextView mtx;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.http);
        Button btn = findViewById(R.id.button2);
        mtx = findViewById(R.id.textView);
        btn.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
        if(v.getId() == R.id.button2){
            sendRequstHttp();
        }
    }

    private void sendRequstHttp() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try{
                    URL url = new URL("https://www.baidu.com");
                    connection = (HttpURLConnection)url.openConnection();
/*                    connection.setRequestMethod("POST");
                    DataOutputStream out = new DataOutputStream(connection.getOutputStream());
                    out.writeBytes("username=admin&password=123456");向服务器传值*/
                    //请求方式
                    connection.setRequestMethod("GET");
                    //连接超出时间
                    connection.setConnectTimeout(8000);
                    //获取内容超时
                    connection.setReadTimeout(8000);
                    InputStream in =connection.getInputStream();
                    reader = new BufferedReader((new InputStreamReader(in)));
                    StringBuilder response = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null){
                        response.append(line);
                    }
                    showResponse(response.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() {
                mtx.setText(response);
            }
        });
    }
}

完整xml文件

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <Button
        android:id="@+id/button2"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Button" />

    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <TextView
            android:id="@+id/textView"
            android:layout_width="match_parent"
            android:layout_height="wrap_content" />
    </ScrollView>


</LinearLayout>

需要在AndroidManifest.xml中添加权限

<uses-permission android:name="android.permission.INTERNET" />

二.使用OkHttp

①首先在app/build.gradle文件中的dependencies闭包添加如下内容

implementation 'com.squareup.okhttp3:okhttp:3.11.0'

②然后创建一个OkHttpClient的实例

OkHttpClient client = new OkHttpClient();

③创建一个Request对象

Request request = new Request.Builder().url("https://www.baidu.com").build();

④调用OkHttpClient的newCall方法来创建一个Call对象，并调用它的execute()方法来发生请求并获取服务器返回的数据

 Response response = client.newCall(request).execute();

⑤用如下方法获取具体内容

String responseData = response.body().string();

使用POST请求

如果发起一条POST请求，首先构建一个RequestBody对象来存放代提交的参数

RequestBody requestBody = new FormBody.Builder().add("1","1").build();

然后在Request.Builder中调用post()方法，并将RequestBody对象传入

Request request = new Request.Builder().url("https://www.baidu.com").post(requestBody).build();

具体代码如下

package com.example.administrator.myapplication;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;

import okhttp3.FormBody;
import okhttp3.OkHttpClient;
import okhttp3.Request;
import okhttp3.RequestBody;
import okhttp3.Response;
import okhttp3.ResponseBody;

public class OkHttpActivity extends AppCompatActivity implements View.OnClickListener {
    TextView mtx;
    @Override
    protected void onCreate(Bundle savedInstanceState){
        super.onCreate(savedInstanceState);
        setContentView(R.layout.http);
        Button btn = findViewById(R.id.button2);
        mtx = findViewById(R.id.textView);
        btn.setOnClickListener(this);
    }
    @Override
    public void onClick(View v) {
        if(v.getId() == R.id.button2){
            sendRequestOkHttp();
        }
    }

    private void sendRequestOkHttp() {
        new Thread(new Runnable() {
            @Override
            public void run() {
                try {
                    OkHttpClient client = new OkHttpClient();
/*                    RequestBody requestBody = new FormBody.Builder().add("1","1").build();
                    Request request = new Request.Builder().url("https://www.baidu.com").post(requestBody).build();*/
                    Request request = new Request.Builder().url("https://www.baidu.com").build();
                    Response response = client.newCall(request).execute();
                    String responseData = response.body().string();
                    showResponse(responseData);
                }catch (Exception e){
                    e.printStackTrace();
                }
            }
        }).start();
    }
    private void showResponse(final String response) {
        runOnUiThread(new Runnable() {
            @Override
            public void run() {
                mtx.setText(response);
            }
        });
    }
}