安卓前台向后台-后台向数据库请求数据+JSON+JDBC+MYSQL

• 使用的平台和开发工具：
• 服务端：Eclipse-javaEE版本，Tomcat9.0
• 安卓客户端：Eclipse-JavaSE版本+ADT
• 数据库端mysql
• Windows7操作系统
• JDK
• gson.jar包、mysql驱动包

1. 完成的小案例描述: 在安卓前台发出根据网址访问后台某个页面，后台的页面根据查询条件去利用JDBC连接数据库技术去连接数据库并查询到相应的信息，对这个信息利用第三方gson.jar包的json.toJson()方法把对象转化成String字符串并返回安卓前台，安卓前台拿到字符串后对其进行数据转化，使用json.fromJson(String,Type)转化为对象并显示到屏幕。
2. 错误的修正：一开始直接把ResultSet类型的结果集直接转到安卓前台，让前台用fromJson()进行转化，结果转化报错，后台尝试后台也导入gson包，用toJson()把对象转化成字符串后再给前台，结果还是不行，后来发现是必须把toJson()拿到的结果给前台才行，toJson(对象)不会把里面的对象变成字符串。还有一个，StringBuffer必须创建对象才能使用它的append()方法，一开始报空指针。

先看看运行的结果:

(sql语句取的是第五条数据)

安卓端代码：

   布局部分：item.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="16dp"
     >

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="120dp"
        android:layout_height="80dp"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:scaleType="fitXY"
        android:src="@drawable/timg" />

    <TableLayout
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/imageView1"
        android:layout_marginLeft="14dp"
        android:layout_toRightOf="@+id/imageView1" >

        <TableRow
            android:id="@+id/tableRow1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/textView1"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="姓名:" />

            <TextView
                android:id="@+id/tv_name"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView" />

        </TableRow>

        <TableRow
            android:id="@+id/tableRow2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/textView3"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="性别:" />

            <TextView
                android:id="@+id/tv_gender"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView" />

        </TableRow>

        <TableRow
            android:id="@+id/tableRow3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/textView5"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="年龄:" />

            <TextView
                android:id="@+id/tv_age"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView" />

        </TableRow>

        <TableRow
            android:id="@+id/tableRow4"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" >

            <TextView
                android:id="@+id/textView7"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="身高:" />

            <TextView
                android:id="@+id/tv_hight"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="TextView" />

        </TableRow>
    </TableLayout>

</RelativeLayout>

java代码:PersonActivity.java

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.MalformedURLException;
import java.net.URL;
import com.google.gson.Gson;
import com.google.gson.reflect.TypeToken;
import com.internethttp.R;
import JavaBean.Person;
import android.app.Activity;
import android.os.AsyncTask;
import android.os.Bundle;
import android.widget.TextView;

public class PersonActivity  extends Activity{ 
	TextView tv_name,tv_gender,tv_age,tv_hight;
	String URL="http://ly-and-tl.uicp.cn:42696/AndroidServer/jsonServlet";
    @Override
    protected void onCreate(Bundle savedInstanceState) {
    	// TODO Auto-generated method stub
    	super.onCreate(savedInstanceState);
    	setContentView(R.layout.item);
    	init();
    	new TASK().execute(URL);
    }
    
    void init(){
    	tv_name=(TextView) findViewById(R.id.tv_name);
    	tv_gender=(TextView) findViewById(R.id.tv_gender);
    	tv_age=(TextView) findViewById(R.id.tv_age);
    	tv_hight=(TextView) findViewById(R.id.tv_hight);
    }
    
    class TASK  extends  AsyncTask<String, Void, Person>{
    	
		@Override
		protected void onPostExecute(Person result) {
			// TODO Auto-generated method stub
			if(result!=null){
				tv_name.setText(result.getName());
				tv_gender.setText(result.getSex());
				tv_age.setText(String.valueOf(result.getAge()));
				tv_hight.setText(String.valueOf(result.getHight()));
			}
		}

		@SuppressWarnings("finally")
		@Override
		protected Person doInBackground(String... arg0) {
			// TODO Auto-generated method stub
			Person person=null;
			String Url=arg0[0];
			String  str=null;
			StringBuffer sb=new StringBuffer();
			
			try {
				URL url=new URL(Url);
				HttpURLConnection  httpconn=(HttpURLConnection) url.openConnection();
				httpconn.setRequestMethod("GET");
				httpconn.setReadTimeout(5000);
				InputStream inputStream=httpconn.getInputStream();
				InputStreamReader inputReader=new InputStreamReader(inputStream);
				BufferedReader buff=new BufferedReader(inputReader);
				while((str=buff.readLine())!=null){
					sb.append(str);
				}
				Gson gson=new Gson();
				String ss=new String(sb);
				System.out.println(ss);
//前台对json字符串开始转化为对象
	            person=gson.fromJson(ss, new TypeToken<Person>(){}.getType());
	            System.out.println(person.getName());
			} catch (MalformedURLException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (IOException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}finally{
				return person;
			}
		}
    }
}

安卓端的java部分的javaBean,Person.java

public class Person{
	private String id;
	private String name;
	private String sex;
	private int age;
	private float hight;
	private float weight;

	public String getId() {
		return id;
	}
	public void setId(String id) {
		this.id = id;
	}
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
	public String getSex() {
		return sex;
	}
	public void setSex(String sex) {
		this.sex = sex;
	}
	public int getAge() {
		return age;
	}
	public void setAge(int age) {
		this.age = age;
	}
	public float getHight() {
		return hight;
	}
	public void setHight(float hight) {
		this.hight = hight;
	}
	public float getWeight() {
		return weight;
	}
	public void setWeight(float weight) {
		this.weight = weight;
	}
}

接下来是服务端的代码：

服务端的web.xml的部署：

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://xmlns.jcp.org/xml/ns/javaee" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" id="WebApp_ID" version="3.1">
  <display-name>AndroidServer</display-name>
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.htm</welcome-file>
    <welcome-file>index.jsp</welcome-file>
    <welcome-file>default.html</welcome-file>
    <welcome-file>default.htm</welcome-file>
    <welcome-file>default.jsp</welcome-file>
  </welcome-file-list>
  
  <servlet>
    <servlet-name>a</servlet-name>
    <servlet-class>android.Internet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>a</servlet-name>
    <url-pattern>/b</url-pattern>
  </servlet-mapping>
  <servlet>
    <servlet-name>son</servlet-name>
    <servlet-class>android.JsonServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>son</servlet-name>
    <url-pattern>/jsonServlet</url-pattern>
  </servlet-mapping>
</web-app>

服务端的主要的页面代码，也就是安卓客户端连接的那个页面，JsonServlet.java

服务端用到了gson.jar，得把它放到tomcat的lib目录下才可以。

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import com.google.gson.Gson;
import DataBase.DataBaseConnection;
import DataBase.StudentHealthJavaBean;

public class JsonServlet extends HttpServlet {

	@Override
	protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO 自动生成的方法存根
		// super.doGet(req, resp);
                PreparedStatement prepare = null;
		ResultSet result = null;
		Connection con = null;
		String sql = "select * from stu_info where id=?";
		StudentHealthJavaBean student=null;
		String str=null;
		con = DataBaseConnection.getConnection();
		try {
			prepare = con.prepareStatement(sql);
			prepare.setString(1, "5");
			result = prepare.executeQuery();
			if (result != null) {
				student= new StudentHealthJavaBean();
				if (result.next()) {
					student.setName(result.getString("name"));
					student.setAge(result.getInt("age"));
					student.setId(result.getString("id"));
					student.setSex(result.getString("sex"));
					student.setHight(result.getFloat("hight"));
					student.setWeight(result.getFloat("weight"));
					Gson json=new Gson();
				 str=json.toJson(student);
//使用json包提供的转化为字符串
				}
				resp.setCharacterEncoding("utf-8");
				PrintWriter p = resp.getWriter();
				p.println(str);
//把json字符串给前台
				p.flush();
			}
			DataBaseConnection.closeDatabaseConnection(con, prepare, result);

		} catch (SQLException e) {
			// TODO 自动生成的 catch 块
			e.printStackTrace();
		}

	}

	@Override
	protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
		// TODO 自动生成的方法存根
		super.doPost(req, resp);
	}

}

服务端的数据库连接部分代码：

public class DataBaseConnection {
	public static String url1="jdbc:mysql://localhost:3306/";
    public static String databaseName="students";
    public static String userName="&user=root";
    public static String password="&password=root";
    public static String driverName="com.mysql.jdbc.Driver";
    public static String encoding="&useUnicode=true&characterEncoding=UTF-8";
    public static String url=url1+databaseName+"?"+"useSSL=false"+encoding+userName+password;
      @SuppressWarnings("finally")
	public static Connection getConnection() {
   	   Connection con=null;
   	     try {
				Class.forName(driverName);
				con=DriverManager.getConnection(url);
			} catch (ClassNotFoundException | SQLException e) {
				// TODO 自动生成的 catch 块
				e.printStackTrace();
			}finally {
				return con;
			}
      }
    
      public static void closeDatabaseConnection(Connection con,PreparedStatement ps,ResultSet rs) {
			try {
		    	   if(rs!=null)rs.close();
				if(ps!=null) ps.close();
		    	if(con!=null) con.close();
			} catch (SQLException e) {
				// TODO 自动生成的 catch 块
				e.printStackTrace();
			}
      }
}

 服务端的javabean和安卓端的一样，字段名和数据库一模一样就OK

public class StudentHealthJavaBean {
	private String id;
	private String name;
	private String sex;
	private int age;
	private float hight;
	private float weight;
	
	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	public String getName() {
		return name;
	}

	public void setName(String name) {
		this.name = name;
	}

	public String getSex() {
		return sex;
	}

	public void setSex(String sex) {
		this.sex = sex;
	}

	public int getAge() {
		return age;
	}

	public void setAge(int age) {
		this.age = age;
	}

	public float getHight() {
		return hight;
	}

	public void setHight(float hight) {
		this.hight = hight;
	}

	public float getWeight() {
		return weight;
	}
	public void setWeight(float weight) {
		this.weight = weight;
	}
	public StudentHealthJavaBean() {
		// TODO 自动生成的构造函数存根
	}

}