我想通过我的 Android 应用程序通过 java servlet 访问本地主机上的 mysql 数据库。我能够通过 java 类访问数据库，但是当在我的 android Activity 中尝试相同的代码时，它不起作用。下面是我的java servlet、java类的代码，我通过它成功访问了我的数据库和android代码，但它不起作用。在我的 LogCat 日志中，我获取了 BufferedReader 类之前的所有日志。另请告诉我在 Android 中可以使用哪个小部件来显示响应字符串。我知道目前我的响应字符串将包含 HTML 代码，但这并不重要，我只是想知道我是否能够访问我的数据库。谢谢。 Java Servlet 代码:
package org.spark.servlet;
import java.io.IOException;
import java.io.PrintWriter;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
/**
* Servlet implementation class HelloServlet2
*/
@WebServlet("/HelloServlet2")
public class HelloServlet2 extends HttpServlet {
private static final long serialVersionUID = 1L;
public void service(HttpServletRequest request,HttpServletResponse response)throws IOException, ServletException{
response.setContentType("text/html");
PrintWriter out = response.getWriter();
out.println("<html>");
out.println("<head><title>Hello World</title></head>");
out.println("<body>");
out.println("<h1>Hello World2</h1>");
// connecting to database
Connection con = null;
Statement stmt = null;
ResultSet rs = null;
try {
Class.forName("com.mysql.jdbc.Driver");
con =DriverManager.getConnection ("jdbc:mysql://localhost:3306", "root", "password");
stmt = con.createStatement();
rs = stmt.executeQuery("Use servlettest");
rs = stmt.executeQuery("SELECT * FROM servlet");
// displaying records
while(rs.next()){
out.print(rs.getObject(1).toString());
out.print("\t\t\t");
out.print(rs.getObject(2).toString());
out.print("<br>");
}
} catch (SQLException e) {
throw new ServletException("Servlet Could not display records.", e);
} catch (ClassNotFoundException e) {
throw new ServletException("JDBC Driver not found.", e);
} finally {
try {
if(rs != null) {
rs.close();
rs = null;
}
if(stmt != null) {
stmt.close();
stmt = null;
}
if(con != null) {
con.close();
con = null;
}
} catch (SQLException e) {}
}
out.println("</body></html>");
out.close();
}
}
Java 类代码:
package org.ProjectEuler;
import java.io.*;
import java.net.*;
public class HelloServlet {
public static void main( String [] args ) {
try {
URL url = new URL("http://localhost:8080/HelloServlet/HelloServlet2");
URLConnection conn = url.openConnection();
conn.setDoOutput(true);
BufferedWriter out = new BufferedWriter( new OutputStreamWriter( conn.getOutputStream()));
out.write("username=javaworld\r\n");
out.flush();
out.close();
BufferedReader in = new BufferedReader( new InputStreamReader( conn.getInputStream()));
String response;
while ( (response = in.readLine()) != null ) {
System.out.println( response );
}
in.close();
}
catch ( MalformedURLException ex ) {
// a real program would need to handle this exception
}
catch ( IOException ex ) {
// a real program would need to handle this exception
}
}
}
Andriod 代码:
package org.spark.mysqltest;
import android.app.Activity;
import android.os.Bundle;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.util.Log;
import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.net.*;
public class MySqlTestActivity extends Activity {
EditText test;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Log.d("checked","checked");
System.out.println("check");
Log.d("checked2","checked2");
test = (EditText) findViewById(R.id.mtv);
Log.d("checked3","checked3");
setContentView(R.layout.main);
Log.d("checked4","checked4");
try {
Log.d("checked5","checked5");
URL url = new URL("http://localhost:8080/HelloServlet/HelloServlet2");
URLConnection conn = url.openConnection();
conn.setDoOutput(true);
Log.d("checked6","checked6");
BufferedWriter out = new BufferedWriter( new OutputStreamWriter( conn.getOutputStream()));
Log.d("checked7","checked7");
out.write("username=javaworld\r\n");
Log.d("checke","checke");
out.flush();
Log.d("check","check");
out.close();
Log.d("chec","chec");
BufferedReader in = new BufferedReader( new InputStreamReader( conn.getInputStream()));
Log.d("che","che");
String response;
while ( (response = in.readLine()) != null ) {
System.out.println( response );
// test.setText(response);
Log.d("checked8","checked8");
}
Log.d("checked9","checked9");
in.close();
}
catch ( MalformedURLException ex ) {
// a real program would need to handle this exception
}
catch ( IOException ex ) {
// a real program would need to handle this exception
}
}
}
最佳答案
第一个问题:您在创建 InputStreamReader 时没有指定编码。这意味着您将使用平台默认编码，该编码可能不是用于创建 Web 响应的编码。 (创建请求时也是如此。)
第二个问题:您忽略任何异常:
catch ( MalformedURLException ex ) {
// a real program would need to handle this exception
}
catch ( IOException ex ) {
// a real program would need to handle this exception
}
我的猜测是抛出了一个异常，但你不知道，因为你甚至没有记录就吞下了这些异常。至少，在此处添加登录功能，我想您会看到出了什么问题。您几乎永远不应该有这样的空catch语句。
顺便问一下，您有什么理由使用这样的低级 API 吗？使用良好的高级 HTTP 客户端库可能会让您的生活变得更加简单。
关于java - BufferedReader 类在 Android Activity 中不起作用，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/10810671/