Android端通过http访问web端servlet获取数据

　　关于wjm的这次作业，当我发现我必须要写APP的时候，我的心是拔凉拔凉的。我疯狂地查资料查博客，本想通过开通mysql远程连接，andriod直接通过pc的ip地址访问mysql，也就是android直连mysql。无奈android开发平台是基于Android Studio的，其不可导入mysqk的jdbc.jar包，出现如Android Studio已有sql资源包，不可再导入此类jar包的错误。查找了半天也没找出解决的办法。讲道理我假期还是有认真学过一点Android，但是这个确实是搞了半天都没能实现啊。

　　好在这时候发现可以通过一种基于servlet为服务器的中转实现方式，其主要的思路为：通过servlet搭建的服务器将mysql中需要的数据取出来发布在以tomcat为支持的网页上，android端直接访问该网页，将网页中的数据全部取出。然后第二天就停了一天的电，晚上7点才来电，好在2小时左右就解决了。下面直接上代码，有问题请自行查阅相关资料或在博客下方留言(我看到了会回复的)。

Android端MainActivity

package com.example.baiducs;

import androidx.appcompat.app.AppCompatActivity;

import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import java.io.BufferedInputStream;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.Reader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.ProtocolException;
import java.net.URL;

public class MainActivity extends AppCompatActivity {
    private TextView textView;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        findViewById(R.id.send_request).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                send();
            }
        });

        textView = (TextView) findViewById(R.id.response_data);
    }

    private void send() {
        //开启线程，发送请求
        new Thread(new Runnable() {
            @Override
            public void run() {
                HttpURLConnection connection = null;
                BufferedReader reader = null;
                try {
                    EditText editText =(EditText)findViewById(R.id.editText);
                    String timeend = editText.getText().toString();
                    URL url = new URL("http://10.0.2.2:8080/ydyq/dengluServlet?timeend="+timeend);
                    //URL url = new URL("https://www.baidu.com/");
                    connection = (HttpURLConnection) url.openConnection();
                    //设置请求方法
                    connection.setRequestMethod("GET");
                    //设置连接超时时间（毫秒）
                    connection.setConnectTimeout(5000);
                    //设置读取超时时间（毫秒）
                    connection.setReadTimeout(5000);

                    //返回输入流
                    InputStream in = connection.getInputStream();

                    //读取输入流
                    reader = new BufferedReader(new InputStreamReader(in));
                    StringBuilder result = new StringBuilder();
                    String line;
                    while ((line = reader.readLine()) != null) {
                        result.append(line);
                    }
                    show(result.toString());
                } catch (MalformedURLException e) {
                    e.printStackTrace();
                } catch (ProtocolException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (reader != null) {
                        try {
                            reader.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                    if (connection != null) {//关闭连接
                        connection.disconnect();
                    }
                }
            }
        }).start();
    }

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

activity_main.xml

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

    <EditText
        android:id="@+id/editText"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:ems="10"
        android:inputType="textPersonName"
        android:text="" />

    <Button
        android:id="@+id/send_request"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="点击查询"
        />

    <!--带滚动条的视图-->
    <ScrollView
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <!--响应数据-->
        <TextView
            android:id="@+id/response_data"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            />

    </ScrollView>


</LinearLayout>

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.baiducs">
    <uses-permission android:name="android.permission.INTERNET"/>
    <application
        android:usesCleartextTraffic="true"
        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">
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

下面是服务器端

web结构

 

 这里主要就是一个dengluServlet调用方法查询数据库返回给Android端结果，上述MainActivity通过http请求访问到dengluServlet，下面是dengluServlet的代码，web端其余代码不在此给出，有需要的请留言。

package com.jdbc.jss;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.ServletInputStream;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.jdbc.bean.Yiqing;
import com.jdbc.dao.yiqidao;
@WebServlet(name = "dengluServlet",urlPatterns = "/dengluServlet")
public class dengluServlet extends HttpServlet {


    private static final long serialVersionUID = 1L;
     public  dengluServlet() {
            super();
        }

    @Override
    protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {
        response.setContentType("text/html;charset=utf-8");
        request.setCharacterEncoding("utf-8");
        response.setCharacterEncoding("utf-8");
        PrintWriter out = response.getWriter();
        String timeend = request.getParameter("timeend");
        System.out.println(timeend);
            //按时间查询
        //String list =  yiqidao.findss(timeend);
        ArrayList<String> list = new ArrayList<String>();
        list = yiqidao.findss(timeend);
        System.out.println(list);
        out.write(list.toString());
        out.flush();
        out.close();
     }   
    @Override
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
        
    }
}

以上内容我在实现时出现过各种问题同时我也参考了许多博客，这里列出主要的几份博客，希望能解决大家实现过程中出现问题

https://blog.csdn.net/snadijssajskkj/article/details/50554903

https://blog.csdn.net/zfdabc_ok/article/details/98055166

https://blog.csdn.net/zhao_zi_ming_lc/article/details/78302601

https://www.jianshu.com/p/5eee1ef02700