Android开发笔记—Http通信的基础使用

为了获得联网权限，首先要在Manifest文件中注册INTERNET组件

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

new一个线程，Http通信都将在子线程中完成。
在线程中new 一个URL类，构造参数传入url地址

    String strUrl = "http://wthrcdn.etouch.cn/weather_mini?city=%E9%95%BF%E6%B2%99";//地址为一个天气API的接口，发送城市名字，返回json数据。
    URL url = new URL(strUrl);

然后通过url对象打开一个连接

url.openConnection();

返回一个URLConnection对象，在Android中使用HttpURLConnection

HttpURLConnection httpUrlConnection = (HttpURLConnection) url.openConnection();

再使用HttpURLConnection 对象打开一个字节输入流

InputStream is = httpURLConnection.getInputStream();

将字节输入流通过new InputStreamReader的方式转换成字符流并缓存BufferedReader类里

BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));

循环从BufferedReader类中读出数据

String str_line = "";
String result = "";
while ((str_line = bufferedReader.readLine()) != null){
    result += str_line;
}

自此已经完成了从互联网读取数据的步骤，并已经将数据存储到String变量result中，下面通过Handler类将数据从子线程传回主线程。

先在主线程中创建一个Handler类，并重写handleMessage方法

Handler myHandler = new Handler(){
    @Override
    public void handleMessage(Message msg) {
        super.handleMessage(msg);

    }
}

然后回到子线程，将数据通过myHandler传给主线程
先创建一个Bundle对象，存储result数据

Bundle b = new Bundle();
b.putString("sk_info", result);

创建一个Message对象，将Bundle对象存储，最后使用myHandler中的sendMessage()发送消息

Message msg = new Message();
msg.setData(b);
myHandler.sendMessage(msg);

当sendMessage后，主线程中重写的handleMessage方法就会接收到
同样的创建一个Bundle对象接收

Bundle b = msg.getData();
String result = b.getString("sk_info");

自此就已经完成了子线程Http通信并且传值给主线程。

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完整代码是一个读取天气的小程序：
xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.example.jialin.httptest.MainActivity">
    <EditText
        android:id="@+id/edit_city"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入城市名称，如：长沙"
        />
    <Button
        android:id="@+id/btn_query"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/edit_city"
        android:text="查询"
        />
    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:text="Hello World!"
        android:layout_below="@id/btn_query"
        />
</RelativeLayout>

Java文件：

package com.example.jialin.httptest;

import android.os.Handler;
import android.os.Message;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import org.json.JSONException;
import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.UnsupportedEncodingException;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import java.net.URLEncoder;

public class MainActivity extends AppCompatActivity {
    public Handler myHandler;
    private Button btn_query;
    private EditText edit_city;
    private TextView textView;
    private String strUrl;
    private JSONObject jsonObject;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        textView = (TextView) findViewById(R.id.textView1);
        btn_query = (Button) findViewById(R.id.btn_query);
        edit_city = (EditText) findViewById(R.id.edit_city);

        btn_query.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String str_city = edit_city.getText().toString();
                if(str_city.length() < 1){
                    Toast.makeText(MainActivity.this, "请输入城市！", Toast.LENGTH_SHORT).show();
                    return ;
                }
                //开始获取API信息
                try {
                    strUrl = "http://wthrcdn.etouch.cn/weather_mini?city=" + URLEncoder.encode (str_city,"UTF-8");
                    new Thread(new Runnable() {
                        @Override
                        public void run() {
                            try {
                                URL url = new URL(strUrl);
                                HttpURLConnection httpURLConnection = (HttpURLConnection) url.openConnection();
                                InputStream is = httpURLConnection.getInputStream();
                                BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(is));
                                String str_line = "";
                                String result = "";
                                while ((str_line = bufferedReader.readLine()) != null){
                                    result += str_line;
                                }
                                Bundle b = new Bundle();
                                b.putString("sk_info", result);
                                Message msg = new Message();
                                msg.setData(b);
                                myHandler.sendMessage(msg);

                            } catch (MalformedURLException e) {
                                e.printStackTrace();
                            } catch (IOException e) {
                                e.printStackTrace();
                            }
                        }
                    }).start();
                } catch (UnsupportedEncodingException e) {
                    e.printStackTrace();
                }
            }
        });

        myHandler = new Handler(){
            @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);
                Bundle b = msg.getData();
                String getResult = b.getString("sk_info");
                try {
                    jsonObject = new JSONObject(getResult).getJSONObject("data");
                    String s = "当前城市：" + jsonObject.getString("city");
                    s += "\n当前气温：" + jsonObject.getString("wendu");
                    s += "\n友情提示：" + jsonObject.getString("ganmao");
                    textView.setText(s);
                } catch (JSONException e) {
                    e.printStackTrace();
                }

            }
        };
    }
}

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示例下载 - GitHub