HttpServlet 在 doPost() 中从 Android 客户端接收 Null

Question

我正在尝试将一些数据从 Android 客户端发送到 HttpServlet。我的Servlet代码如下

import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.SQLException;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;


public class DBServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
Connection connection= null;   

/**
 * @see HttpServlet#HttpServlet()
 */
public DBServlet() {
        super();
}

/**
 * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
 */
protected void doGet(HttpServletRequest request, HttpServletResponse response) 
        throws ServletException, IOException {

    doPost(request, response);
}

/**
 * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
 */
protected void doPost(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

    if(request.getParameterNames().hasMoreElements()){
                insertRecord(request, getDbConnection());
            }
            else{ System.out.println("Servlet Started First Time"); }



}

/**
 * Return database connection
 * @return
 */
private Connection getDbConnection(){
        String connectionURL = "jdbc:mysql://127.0.0.1:3306/testDB";

        try {

            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection(connectionURL, "root", "");

        } catch (SQLException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        return connection;  
}

/**
 * Insert record in database
 * @param request
 * @param connection
 */
private void insertRecord(HttpServletRequest request, Connection connection){   

            System.out.println("===== Received Record =====");

            PreparedStatement stmt;

            try {
                stmt = connection.prepareStatement("insert into users(Name,email,password) values(?,?,?)");
                stmt.setString(1, request.getParameter("name"));
                stmt.setString(2, request.getParameter("e-mail"));
                stmt.setString(3, request.getParameter("password"));

                int i= stmt.executeUpdate();

                if(i != 0){
                    System.out.println("data inserted !!!");
                }
                else{
                    System.out.println("data failed to insert");
                }

            } catch (SQLException e) {
                e.printStackTrace();
            }

            finally{

                try {
                    connection.close();
                } catch (SQLException e) {

                    e.printStackTrace();
                }
            }
    }
}

我的安卓代码是

import java.io.DataOutputStream;
import java.io.IOException;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;

import org.apache.http.NameValuePair;

import org.apache.http.message.BasicNameValuePair;

import com.example.messenger.R;

import android.annotation.SuppressLint;
import android.app.Activity;
import android.os.Bundle;
import android.os.StrictMode;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

public class SignUp extends Activity {

Button register;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.sign_up);

    register = (Button)findViewById(R.id.register);

    register.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            Log.v("OnClick", "=== onClick ===");
            registerUser();

        }
    });
}

@SuppressLint({ "NewApi", "NewApi", "NewApi" })
private void registerUser(){


        String name= ((EditText)findViewById(R.id.name)).getText().toString();
        String email= ((EditText)findViewById(R.id.email)).getText().toString();
        String password= ((EditText)findViewById(R.id.password)).getText().toString();

        ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
        nameValuePairs.add(new BasicNameValuePair("name", name));
        nameValuePairs.add(new BasicNameValuePair("email", email));
        nameValuePairs.add(new BasicNameValuePair("password", password));


        try {

            StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
            StrictMode.setThreadPolicy(policy);

            URL url=new URL("http://192.168.1.10:8080/DBservlet/DBServlet");
            HttpURLConnection con = (HttpURLConnection)url.openConnection();
            con.setDoOutput(true);
            con.setRequestMethod("POST");
            DataOutputStream dos=new DataOutputStream(con.getOutputStream());
            dos.writeBytes(name);
            dos.flush();
            dos.close();

}  catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

}

}

问题是，当我运行“Servlet”时，我得到输出“Servlet Started First Time”，这没问题，但是当我运行我的 android 客户端并在 EditText 字段中写入一些数据并按下注册按钮时，没有任何反应。 'Servlet' 什么也没收到。请告诉我如何解决这个问题。

问候，

Answer 1

您的 servlet 在功能上看起来不错（设计技术上不是，但那是另一回事）。不过你的 Android 端看起来肯定不好。

这个，

ArrayList<NameValuePair> nameValuePairs = new ArrayList<NameValuePair>();
nameValuePairs.add(new BasicNameValuePair("name", name));
nameValuePairs.add(new BasicNameValuePair("email", email));
nameValuePairs.add(new BasicNameValuePair("password", password));

是您在使用 Android 内置 Apache HttpClient API 发送 HTTP 请求之前准备请求参数的方式。

但是在这里，

URL url=new URL("http://192.168.1.10:8080/DBservlet/DBServlet");
HttpURLConnection con = (HttpURLConnection)url.openConnection();
con.setDoOutput(true);
con.setRequestMethod("POST");
DataOutputStream dos=new DataOutputStream(con.getOutputStream());
dos.writeBytes(name);
dos.flush();
dos.close();

但是，您正在使用 Java SE 内置 URLConnection API 发送 HTTP 请求。然后实际上以一种糟糕的方式；您发送的不是正确的 application/x-www-form-urlendocded 查询字符串，而是平台默认编码中的单个字符串值。同样DataOutputStream 在这种情况下完全没有意义，你根本没有创建.dat 文件。这感觉太像“roseindia.net-sn-p”了。如果您确实在阅读那个糟糕的网站，请从现在开始将其列入终身黑名单。

您似乎在混合使用 不同 在 Android 中发送 HTTP POST 请求的方法。

1. Using HttpClient API
2. Using URLConnection API

你应该选择其中一个并坚持下去。上面的链接指向 Stack Overflow 答案风格的具体示例。