Question

嗨，我有使用JDBC的java程序，我已经使用了线程但是我这样得到了例外：

Exception in thread "Thread-1964" java.lang.OutOfMemoryError: Java heap space

我认为因为我无限启动线程并且还没有关闭

所以，我想使用线程池，sp该线程来自池，并在执行任务后将其打包到池中。

这是我的java代码：

public class DBTestCases{

    Connection localConnection; 
    Connection remoteConnection;
    Connection localCon;
    Connection remoteCon;
    List<Connection> connectionsList;
    String driver = "com.mysql.jdbc.Driver";
    String user = "root";
    String password = "root";
    String dbName = "myDB";
    String connectionUrl1= "jdbc:mysql://11.232.33:3306/"+dbName+"?user="+user+"&password="+password+"&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&maxReconnects=10";
    String connectionUrl2= "jdbc:mysql://localhost:3306/"+dbName+"?user="+user+"&password="+password+"&useUnicode=true&characterEncoding=UTF-8&autoReconnect=true&failOverReadOnly=false&maxReconnects=10";

    public List<Connection> createConnection() {

        try {
                    Class.forName(driver);
                    localCon = DriverManager.getConnection(connectionUrl2);
                    if(localCon != null)
                        System.out.println("connected to remote database at : "+new Date());
                    remoteCon = DriverManager.getConnection(connectionUrl1);
                    if(remoteCon != null)
                        System.out.println("connected to local database at : "+new Date());
                    connectionsList = new ArrayList<Connection>( 2 );
                    connectionsList.add( 0 , localCon );
                    connectionsList.add( 1 , remoteCon );
                } catch(ClassNotFoundException cnfe) {
                    cnfe.printStackTrace();
                    } catch(SQLException sqle) {
                        sqle.printStackTrace();
                        }
        return connectionsList;
    }

    public void insert(){

        Runnable runnable = new Runnable(){
        public void run() {
        PreparedStatement ps1 = null;
        PreparedStatement ps2 = null;
        String sql = "insert into user1(name, address, created_date)" +
                                " values('johnsan', 'usa', '2013-08-04')";
        if(remoteConnection != null&&localConnection != null) {
            System.out.println("Database Connection Is Established");
            try {
                        ps1 = remoteConnection.prepareStatement(sql);
                        ps2 = localConnection.prepareStatement(sql);
                        int i = ps1.executeUpdate();
                        int k = ps2.executeUpdate();
                        if(i > 0) {
                            System.out.println("Data Inserted into remote database table Successfully");
                        }
                        if(k > 0) {
                            System.out.println("Data Inserted into local database table Successfully");
                        }
                    } catch (SQLException s) {
                            System.out.println("SQL code does not execute.");
                            s.printStackTrace();
                        }catch (Exception e) {
                            e.printStackTrace();
                        }
            }
            System.out.println("Inserting values in db");
        }
        };
        Thread thread = new Thread(runnable);
        thread.start();
    }

    public void retrieve(){

        Runnable runnable = new Runnable(){
        public void run() {
        try {
                    Statement st1 = localConnection.createStatement();
                    Statement st2 = remoteConnection.createStatement();
                    ResultSet res1 = st1.executeQuery("SELECT * FROM  user1");
                    ResultSet res2 = st2.executeQuery("SELECT * FROM  user1");
                    System.out.println("---------------------------Local Database------------------------");
                    while (res1.next()) {
                        Long i = res1.getLong("userId");
                        String s1 = res1.getString("name");
                        String s2 = res1.getString("address");
                        java.sql.Date d = res1.getDate("created_date");
                        System.out.println(i + "\t\t" + s1 + "\t\t" + s2 + "\t\t"+ d);
                    }
                    System.out.println("------------------------Remote Database---------------------");
                    while (res2.next()) {
                        Long i = res2.getLong("userId");
                        String s1 = res2.getString("name");
                        String s2 = res2.getString("address");
                        java.sql.Date d = res2.getDate("created_date");
                        System.out.println(i + "\t\t" + s1 + "\t\t" + s2 + "\t\t"+ d);
                    }
        } catch (SQLException s) {
                System.out.println("SQL code does not execute.");
                s.printStackTrace();
        }catch (Exception e) {
                e.printStackTrace();
        }
        }
        };
        Thread thread = new Thread(runnable);
        thread.start();
    }

    public static void main(String[] args) {
        DBTestCases dbTestCases = new DBTestCases();
        List l = dbTestCases.createConnection();
        dbTestCases.localConnection = (Connection)l.get(0);
        dbTestCases.remoteConnection = (Connection)l.get(1);
        for(;;) {
            dbTestCases.insert();
            dbTestCases.countRows();
            dbTestCases.retrieve();
        }
    }
}

请告诉我如何将此程序修改为使用线程池..因此我不会得到该异常

提前谢谢

Answer 1

对于线程池，请使用ExecutorService：

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/ExecutorService.html

例如ThreadPoolExecutor：

http://docs.oracle.com/javase/6/docs/api/java/util/concurrent/ThreadPoolExecutor.html

在程序中使用ThreadPool

1 个答案: