java JDBC/MYSQL通信链路故障（ECLIPSE/ANDROID）
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并检索/println结果
我正在使用本教程，从教程点到安卓代码：
http://www.tutorialspoint.com/jdbc/jdbc-sample-code.htm
以下是我采用的版本：
package com.example.myfirstapp0006;
import 安卓.support.v7.app.ActionBarActivity;
import 安卓.os.Bundle;
import 安卓.view.Menu;
import 安卓.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
我收到这些错误：
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 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-03 18:55:14.883: W/System.err(389): at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
11-03 18:55:14.883: W/System.err(389): at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
11-03 18:55:14.883: W/System.err(389): at 安卓.app.ActivityThread.access$2300(ActivityThread.java:125)
11-0 18:55:14.883: W/System.err(389): at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
11-03 18:55:14.883: W/System.err(389): at 安卓.os.Handler.dispatchMessage(Handler.java:99)
11-03 18:55:14.894: W/System.err(389): at 安卓.os.Looper.loop(Looper.java:123)
11-03 18:55:14.894: W/System.err(389): at 安卓.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.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-03 18:55:14.894: W/System.err(389): at com.安卓.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
# 1 楼答案
这通常发生在MySQL达到最大并发连接数时。尝试重新启动MySQL
如果需要更多并发连接，可以更新我的。cnf通过在[mysqld]下添加这一行：
其中x是最大并发连接数
您可以通过运行以下命令查看活动连接的数量：
MySQL网站上还有更多信息：
http://dev.mysql.com/doc/refman/5.5/en/too-many-connections.html
# 2 楼答案
你在哪里安装了mysql？ 尝试更改url中的主机；现在您正在尝试连接到本地主机： 静态最终字符串DB_URL=“jdbc:mysql://localhost/EMP“
你不能在android手机上运行mysql，如果你想在本地执行它，你可以选择其他数据库（例如，你可以使用SQLite）
# 3 楼答案
Android默认内置了SqlLite数据库。您是否将mysql数据库作为附加软件包安装。你的mysql数据库在哪里
参考此link