Android中网络相关的技术，主要分别两种，一种为直接显示网页，另外一种为获取服务器中的数据进行设置。

权限声明

访问网络是需要声明权限

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.webviewtest">

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

    ...

</manifest>

WebView的使用

通过WebView的控件，直接显示网页，不需要考虑网页中的具体数据。

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        webView.settings.javaScriptEnabled=true
        webView.webViewClient = WebViewClient()
        webView.loadUrl("http://www.baidu.com")
    }

}

调用了WebView的setWebViewClient()方法，并传入了一个WebViewClient的实例。这段代码的作用是，当需要从一个网页跳转到另一个网页时，我们希望目标网页仍然在当前WebView中显示，而不是打开系统浏览器。

HttpURLConnection的使用

get获取数据

class MainActivity : AppCompatActivity() {

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_main)
        sendRequestBtn.setOnClickListener {
            sendRequestWithHttpURLConnection()
        }
    }

    private fun sendRequestWithHttpURLConnection() {
        // 开启线程发起网络请求
        thread {
            var connection: HttpURLConnection? = null
            try {
                val response = StringBuilder()
                val url = URL("http://www.baidu.com")
                connection = url.openConnection() as HttpURLConnection
                connection.connectTimeout = 8000
                connection.readTimeout = 8000
                val input = connection.inputStream
                // 下面对获取到的输入流进行读取
                val reader = BufferedReader(InputStreamReader(input))
                reader.use {
                    reader.forEachLine {
                        response.append(it)
                    }
                }
            } catch (e: Exception) {
                e.printStackTrace()
            } finally {
                connection?.disconnect()
            }
        }
    }
    }
}

post发送数据

connection.requestMethod = "POST"
val output = DataOutputStream(connection.outputStream)
output.writeBytes("username=admin&password=123456")

okHttp的使用

项目主页地址：
http://github.com/square/okhttp
添加依赖：

dependencies {
    ...
    implementation 'com.squareup.okhttp3:okhttp:4.1.0'
}

版本根据官网中的最新版本进行添加

okHttp的具体用法

获取Client的实例

val client = OkHttpClient()

创建get的request实例

创建request，需要知道是否需要设置token

val request = Request.Builder()
        .url("http://www.baidu.com")
        .build()

获取response

同步获取

val response = client.newCall(request).execute()
val responseData = response.body?.string()

异步获取：

   client.newCall(request).enqueue(new Callback() {
            @Override
            public void onFailure(@NotNull Call call, @NotNull IOException e) {
                //响应失败
            }

            @Override
            public void onResponse(@NotNull Call call, @NotNull Response response) throws IOException {
            //响应成功
            val responseData = response.body?.string()

            }
        });

发起Post的请求

val requestBody = FormBody.Builder()
        .add("username", "admin")
        .add("password", "123456")
        .build()
 val request = Request.Builder()
        .url("http://www.baidu.com")
        .post(requestBody)
        .build()

从Android 9.0系统开始，应用程序默认只允许使用HTTPS类型的网络请求，HTTP类型的网络请求因为有安全隐患默认不再被支持，如果使用的是HTTP，需要设置文件，res -> xml ->network_config.xml文件。

<?xml version="1.0" encoding="utf-8"?>
<network-security-config>
    <base-config cleartextTrafficPermitted="true">
        <trust-anchors>
            <certificates src="system" />
        </trust-anchors>
    </base-config>
</network-security-config>

这段配置文件是允许我们以明文的方式在网络上传输数据，而HTTP使用的就是明文传输方式。
需要修改manifest文件中的内容，如下所示：

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.networktest">
    ...
    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        android:networkSecurityConfig="@xml/network_config">
        ...
    </application>
</manifest>

解析XML数据的两种方法：

①pull方法

方法parseXMLWithPull中的，即为使用Pull方法解析XML格式的数据

class MainActivity : AppCompatActivity() {
...
private fun sendRequestWithOkHttp() {
thread {
try {
val client = OkHttpClient()
val request = Request.Builder()
// 指定访问的服务器地址是计算机本机
.url("http://10.0.2.2/get_data.xml")
.build()
val response = client.newCall(request).execute()
val responseData = response.body?.string()
if (responseData != null) {
parseXMLWithPull(responseData)
}
} catch (e: Exception) {
e.printStackTrace()
}
}
}
...
private fun parseXMLWithPull(xmlData: String) {
try {
val factory = XmlPullParserFactory.newInstance()
val xmlPullParser = factory.newPullParser()
xmlPullParser.setInput(StringReader(xmlData))
var eventType = xmlPullParser.eventType
var id = ""
var name = ""
var version = ""
while (eventType != XmlPullParser.END_DOCUMENT) {
val nodeName = xmlPullParser.name
when (eventType) {
// 开始解析某个节点
XmlPullParser.START_TAG -> {
when (nodeName) {
"id" -> id = xmlPullParser.nextText()
"name" -> name = xmlPullParser.nextText()
"version" -> version = xmlPullParser.nextText()
}
}
// 完成解析某个节点
XmlPullParser.END_TAG -> {
if ("app" == nodeName) {
Log.d("MainActivity", "id is $id")
Log.d("MainActivity", "name is $name")
Log.d("MainActivity", "version is $version")
}
}
}
eventType = xmlPullParser.next()
}
} catch (e: Exception) {
e.printStackTrace()
}
}
}

②SAX方法

class MainActivity : AppCompatActivity() {
...
private fun sendRequestWithOkHttp() {
thread {
try {
val client = OkHttpClient()
val request = Request.Builder()
// 指定访问的服务器地址是计算机本机
.url("http://10.0.2.2/get_data.xml")
.build()
val response = client.newCall(request).execute()
val responseData = response.body?.string()
if (responseData != null) {
parseXMLWithSAX(responseData)
}
} catch (e: Exception) {
e.printStackTrace()
}
}
}
...
private fun parseXMLWithSAX(xmlData: String) {
try {
val factory = SAXParserFactory.newInstance()
val xmlReader = factory.newSAXParser().XMLReader
val handler = ContentHandler()
// 将ContentHandler的实例设置到XMLReader中
xmlReader.contentHandler = handler
// 开始执行解析
xmlReader.parse(InputSource(StringReader(xmlData)))
} catch (e: Exception) {
e.printStackTrace()
}
}
}

ContentHandler的定义：

class ContentHandler : DefaultHandler() {
private var nodeName = ""
private lateinit var id: StringBuilder
private lateinit var name: StringBuilder
private lateinit var version: StringBuilder
override fun startDocument() {
id = StringBuilder()
name = StringBuilder()
version = StringBuilder()
}
override fun startElement(uri: String, localName: String, qName: String, attributes:
Attributes) {
// 记录当前节点名
nodeName = localName
Log.d("ContentHandler", "uri is $uri")
Log.d("ContentHandler", "localName is $localName")
Log.d("ContentHandler", "qName is $qName")
Log.d("ContentHandler", "attributes is $attributes")
}
override fun characters(ch: CharArray, start: Int, length: Int) {
// 根据当前节点名判断将内容添加到哪一个StringBuilder对象中
when (nodeName) {
"id" -> id.append(ch, start, length)
"name" -> name.append(ch, start, length)
"version" -> version.append(ch, start, length)
}
}
override fun endElement(uri: String, localName: String, qName: String) {
if ("app" == localName) {
Log.d("ContentHandler", "id is ${id.toString().trim()}")
Log.d("ContentHandler", "name is ${name.toString().trim()}")
Log.d("ContentHandler", "version is ${version.toString().trim()}")
// 最后要将StringBuilder清空
id.setLength(0)
name.setLength(0)
version.setLength(0)
}
}
override fun endDocument() {
}
}

id、name和version中都可能是包括回车或换行符的，需要调用trim。

解析JSON数据

官方提供的JSONObject，使用Google的开源库GSON。或者使用一些第三方的开源库如Jackson、FastJSON等。

①官方的JSONObject

......
private fun parseJSONWithJSONObject(jsonData: String) {
try {
val jsonArray = JSONArray(jsonData)
for (i in 0 until jsonArray.length()) {
val jsonObject = jsonArray.getJSONObject(i)
val id = jsonObject.getString("id")
val name = jsonObject.getString("name")
val version = jsonObject.getString("version")
Log.d("MainActivity", "id is $id")
Log.d("MainActivity", "name is $name")
Log.d("MainActivity", "version is $version")
}
} catch (e: Exception) {
e.printStackTrace()
}
}
}

②使用GSON解析

添加依赖

dependencies {
...
implementation 'com.google.code.gson:gson:2.8.5'
}

解析一段字符串
{“name”:“Tom”,“age”:20}
设置Person的类，直接进行转换

val gson = Gson()
val person = gson.fromJson(jsonData, Person::class.java)

解析字符串数组
需要借助TypeToken将期望解析成的数据类型传入fromJson()方法中

val typeOf = object : TypeToken<List<Person>>() {}.type
val people = gson.fromJson<List<Person>>(jsonData, typeOf)

jsonData为需要解析的字符串数组

网络请求回调方法：

interface HttpCallbackListener {
fun onFinish(response: String)
fun onError(e: Exception)
}

object HttpUtil {
fun sendHttpRequest(address: String, listener: HttpCallbackListener) {
thread {
var connection: HttpURLConnection? = null
try {
val response = StringBuilder()
val url = URL(address)
connection = url.openConnection() as HttpURLConnection
connection.connectTimeout = 8000
connection.readTimeout = 8000
val input = connection.inputStream
val reader = BufferedReader(InputStreamReader(input))
reader.use {
reader.forEachLine {
response.append(it)
}
}
// 回调onFinish()方法
listener.onFinish(response.toString())
} catch (e: Exception) {
e.printStackTrace()
// 回调onError()方法
listener.onError(e)
} finally {
connection?.disconnect()
}
}
}
}

使用json

object HttpUtil {
...
fun sendOkHttpRequest(address: String, callback: okhttp3.Callback) {
val client = OkHttpClient()
val request = Request.Builder()
.url(address)
.build()
client.newCall(request).enqueue(callback)
}
}

使用

HttpUtil.sendOkHttpRequest(address, object : Callback {
override fun onResponse(call: Call, response: Response) {
// 得到服务器返回的具体内容
val responseData = response.body?.string()
}
override fun onFailure(call: Call, e: IOException) {
// 在这里对异常情况进行处理
}
})