首页
学习
活动
专区
圈层
工具
发布
社区首页 >问答首页 >JDBC/MYSQL通信链接失败(ECLIPSE/ANDROID)

JDBC/MYSQL通信链接失败(ECLIPSE/ANDROID)
EN

Stack Overflow用户
提问于 2014-11-03 19:36:21
回答 3查看 2.1K关注 0票数 0

我一直在尝试制作一个简单的hello world应用程序,它使用jdbc查询mysql和检索/println结果。

我从android代码中采用的教程点开始使用本教程:

http://www.tutorialspoint.com/jdbc/jdbc-sample-code.htm

以下是我采用的版本:

代码语言:javascript
复制
    package com.example.myfirstapp0006;

    import android.support.v7.app.ActionBarActivity;
    import android.os.Bundle;
    import android.view.Menu;
    import android.view.MenuItem;
    import java.sql.*;

    public class MainActivity extends ActionBarActivity {

        // JDBC driver name and database URL
        static final String JDBC_DRIVER = "com.mysql.jdbc.Driver";
        static final String DB_URL = "jdbc:mysql://localhost/EMP";

        // Database credentials
        static final String USER = "username";
        static final String PASS = "password";

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);

            Connection conn = null;
            Statement stmt = null;
            try{
                // STEP 2: Register JDBC driver
                Class.forName("com.mysql.jdbc.Driver");

                // STEP 3: Open a connection
                System.out.println("Connecting to database...");
                conn = DriverManager.getConnection(DB_URL,USER,PASS);

                // STEP 4: Execute a query
                System.out.println("Creating statement...");
                stmt = conn.createStatement();
                String sql;
                sql = "SELECT id, first, last, age FROM Employees";
                ResultSet rs = stmt.executeQuery(sql);

                // STEP 5: Extract data from result set
                while(rs.next()) {
                    // Retrieve by column name
                    int id = rs.getInt("id");
                    int age = rs.getInt("age");
                    String first = rs.getString("first");
                    String last = rs.getString("last");

                    // Display values
                    System.out.println("ID: " + id);
                    System.out.println(", Age: " + age);
                    System.out.println(", First: " + first);
                    System.out.println(", Last: " + last);
                }

                // STEP 6: Clean-up environment
                rs.close();
                stmt.close();
                conn.close();
            }catch(SQLException se){
                //Handle errors for JDBC
                se.printStackTrace();
            }catch(Exception e){
                //Handle errors for Class.forName
                e.printStackTrace();
            }finally{
                //finally block used to close resources
                try{
                    if(stmt != null)
                        stmt.close();
                }catch(SQLException se){
                    se.printStackTrace();
                }//end finally try
            }//end try
            System.out.println("Goodbye!");
        }//end onCreate

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();
        if (id == R.id.action_settings) {
            return true;
        }
        return super.onOptionsItemSelected(item);
    }
}//end MainActivity

I‘s获取这些错误:

代码语言:javascript
复制
11-03 18:55:14.854: W/System.err(389)   com.mysql.jdbc.CommunicationsException: Communications link failure
11-03 18:55:14.854: W/System.err(389):  The last packet sent successfully to the server was 0 milliseconds ago. The driver has not received any packets from the server. 
11-03 18:55:14.854: W/System.err(389):  at  com.mysql.jdbc.SQLError.createCommunicationsException(SQLError.java:1032)
11-03 18:55:14.864: W/System.err(389):  at  com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:338) 
11-03 18:55:14.864: W/System.err(389):  at  com.mysql.jdbc.ConnectionImpl.coreConnect(ConnectionImpl.java:2232)
11-03 18:55:14.864: W/System.err(389):  at  com.mysql.jdbc.ConnectionImpl.connectOneTryOnly(ConnectionImpl.java:2265)
11-03 18:55:14.864: W/System.err(389):  at  com.mysql.jdbc.ConnectionImpl.createNewIO(ConnectionImpl.java:2064)
11-03 18:55:14.864: W/System.err(389):  at  com.mysql.jdbc.ConnectionImpl.<init>(ConnectionImpl.java:790) 
11-0 18:55:14.864:  W/System.err(389):  at  com.mysql.jdbc.ConnectionImpl.getInstance(ConnectionImpl.java:392)
11-03 18:55:14.874: W/System.err(389):  at  com.mysql.jdbc.NonRegisteringDriver.connect(NonRegisteringDriver.java:325)
11-03 18:55:14.874: W/System.err(389):  at  java.sql.DriverManager.getConnection(DriverManager.java:191) 
11-0 18:55:14.874:  W/System.err(389):  at  java.sql.DriverManager.getConnection(DriverManager.java:226) 
11-0 18:55:14.874:  W/System.err(389):  at  com.example.myfirstapp0006.MainActivity.onCreate(MainActivity.java:32)
11-03 18:55:14.874: W/System.err(389):  at  android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-03 18:55:14.883: W/System.err(389):  at  android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
11-03 18:55:14.883: W/System.err(389):  at  android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
11-03 18:55:14.883: W/System.err(389):  at  android.app.ActivityThread.access$2300(ActivityThread.java:125) 
11-0 18:55:14.883:  W/System.err(389):  at  android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
11-03 18:55:14.883: W/System.err(389):  at  android.os.Handler.dispatchMessage(Handler.java:99) 
11-03 18:55:14.894: W/System.err(389):  at  android.os.Looper.loop(Looper.java:123) 
11-03 18:55:14.894: W/System.err(389):  at  android.app.ActivityThread.main(ActivityThread.java:4627) 
11-0 18:55:14.894:  W/System.err(389):  at  java.lang.reflect.Method.invokeNative(Native Method) 
11-0 18:55:14.894:  W/System.err(389):  at  java.lang.reflect.Method.invoke(Method.java:521) 
11-03 18:55:14.894: W/System.err(389):  at  com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-03 18:55:14.894: W/System.err(389):  at  com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
11-0 18:55:14.894:  W/System.err(389):  at  dalvik.system.NativeStart.main(Native Method) 
11-03 18:55:14.894: W/System.err(389):  Caused by: java.net.SocketException: Permission denied 
11-03 18:55:14.904: W/System.err(389):  at  org.apache.harmony.luni.platform.OSNetworkSystem.createStreamSocketImpl(Native Method) 
11-03 18:55:14.904: W/System.err(389):  at  org.apache.harmony.luni.platform.OSNetworkSystem.createStreamSocket(OSNetworkSystem.java:186)
11-03 18:55:14.904: W/System.err(389):  at  org.apache.harmony.luni.net.PlainSocketImpl.create(PlainSocketImpl.java:265)
11-03 18:55:14.904: W/System.err(389):  at  java.net.Socket.startupSocket(Socket.java:774) 
11-03 18:55:14.904: W/System.err(389):  at java.net.Socket.<init>(Socket.java:316) 
11-0 18:55:14.904:  W/System.err(389):  at  com.mysql.jdbc.StandardSocketFactory.connect(StandardSocketFactory.java:243)
11-03 18:55:14.913: W/System.err(389):  at  com.mysql.jdbc.MysqlIO.<init>(MysqlIO.java:297) 
11-03 18:55:14.913: W/System.err(389):  ... 22 more

有什么线索吗?

EN

回答 3

Stack Overflow用户

发布于 2014-11-03 19:40:34

当MySQL达到其最大并发连接数时,通常会发生这种情况。尝试重新启动MySQL。

如果需要更多并发连接,可以通过在mysqld下添加此行来更新my.cnf。

代码语言:javascript
复制
max_connections=x

其中x是并发连接的最大数目。

可以通过运行以下命令查看活动连接的数量:

代码语言:javascript
复制
SHOW STATUS WHERE `variable_name` = 'Threads_connected'

MySQL网站上也有更多的信息:

http://dev.mysql.com/doc/refman/5.5/en/too-many-connections.html

票数 0
EN

Stack Overflow用户

发布于 2014-11-03 19:43:26

默认情况下,Android内置了SqlLite数据库。您是否将mysql数据库作为附加包安装。mysql数据库位于哪里?

请参阅此链接

票数 0
EN

Stack Overflow用户

发布于 2014-11-03 19:50:29

你在哪里安装mysql的?尝试更改url中的主机;现在您正在尝试连接到localhost:静态最终字符串DB_URL = "jdbc:mysql://localhost/EMP";

您不能在android上运行mysql,如果要在本地执行它,可以选择其他db (例如,可以使用SQLite)。

票数 0
EN
页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接:

https://stackoverflow.com/questions/26721704

复制
相关文章

相似问题

领券
问题归档专栏文章快讯文章归档关键词归档开发者手册归档开发者手册 Section 归档