java连接MySQL Eclipse错误

Question

我正在尝试将我的安卓项目连接到mysql中的数据库，这是我的代码：

package br.com.savetime;

导入java。sql.*

公共级CriarConexao{

private static Connection con = null;

public static Connection abrirBanco(){
    Connection con;
    try{
        Class.forName("com.mysql.jdbc.Driver").newInstance();  
        con = DriverManager.getConnection("jdbc:mysql://localhost:3306/savetime", "root", "root");
        return con;

    }
    catch(ClassNotFoundException cnfe){
        System.out.println("driver nao encontrado: " + cnfe.getMessage());
        return null;
    }
    catch(SQLException sql){
        System.out.println("SQLException: " + sql.getMessage());
        return null;
    }
    catch(Exception e){
        System.out.println(e.getMessage());
        return null;
    }
}

public static void fecharBDcon(){
    try{
        con.close();
    }
    catch(Exception e){
        System.out.println("erro ao fechar o banco" + e.getMessage());
    }
}   

}

这就是错误：

06-18 02:32:57.925: I/System.out(1044): SQLException: Communications link failure due to underlying exception: 
06-18 02:32:57.925: I/System.out(1044): ** BEGIN NESTED EXCEPTION ** 
06-18 02:32:57.925: I/System.out(1044): 安卓.os.NetworkOnMainThreadException
06-18 02:32:57.925: I/System.out(1044): STACKTRACE:
06-18 02:32:57.935: I/System.out(1044): 安卓.os.NetworkOnMainThreadException
06-18 02:32:57.935: I/System.out(1044):     at 安卓.os.StrictMode$AndroidBlockGuardPolicy.onNetwork(StrictMode.java:1117)
06-18 02:32:57.935: I/System.out(1044):     at java.net.InetAddress.lookupHostByName(InetAddress.java:385)
06-18 02:32:57.935: I/System.out(1044):     at java.net.InetAddress.getAllByNameImpl(InetAddress.java:236)
06-18 02:32:57.935: I/System.out(1044):     at java.net.InetAddress.getAllByName(InetAddress.java:214)
06-18 02:32:57.935: I/System.out(1044):     at com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:133)
06-18 02:32:57.935: I/System.out(1044):     at com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:280)
06-18 02:32:57.935: I/System.out(1044):     at com.mysql.jdbc.Connection.createNewIO(Connection.java:1765)
06-18 02:32:57.935: I/System.out(1044):     at com.mysql.jdbc.Connection.<init>(Connection.java:430)
06-18 02:32:57.935: I/System.out(1044):     at com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:268)

我没有上网，所以我不明白为什么会发生这个错误，你能帮我吗

Answer 1

首先是在android localhost中，如果您试图从emulator连接到系统上的mysql，请使用10.0.0.2IP连接到系统，这是指它自己的环回地址。对于设备，您必须使用usb连接，并且设备和系统需要位于同一网络上。 其次，使用异步任务进行通信，因为这将是网络调用

Answer 2

您试图打开与应用程序不在本地的数据库的连接。您正在通过网络进行连接，Android（蜂巢和转发）不允许您在UI线程上进行网络调用。使用AsyncTask或其他构造在主（UI）线程之外执行网络操作

[编辑]

下面是一个关于如何使用AsyncTask连接到MySQL的示例：

private class Connect extends AsyncTask<String, Void, String> {
    @Override
    protected String doInBackground(String... urls) {
      String response = "";

      try {
          Class.forName("com.mysql.jdbc.Driver");
          Connection con = DriverManager.getConnection(url, user, pass);
          // System.out.println("Database connection success"); 

          String result = "Database connection success\n";
          Statement st = con.createStatement();
          ResultSet rs = st.executeQuery("select * from users");
          ResultSetMetaData rsmd = rs.getMetaData();

          while(rs.next()) {
            result += rsmd.getColumnName(1) + ": " + rs.getInt(1) + "\n";
            result += rsmd.getColumnName(2) + ": " + rs.getString(2) + "\n";
            result += rsmd.getColumnName(3) + ": " + rs.getString(3) + "\n";
          }
          tv.setText(result);
      }
      catch(Exception e) {
          e.printStackTrace();
          tv.setText(e.toString());
      }
    return response;   


    }

另外，代码取自here