Connection关闭时报错
我想要写一个定时访问数据库，读取数据里的数据但是我没法关闭Connection链接，请问怎么解决？下面是我代码
public class UploadFileDao {
private Connection conn = null;
private PreparedStatement pstmt = null;
private ResultSet rs = null;
public List<UploadFile> listUploadFile() {
List<UploadFile> uploadFile_l = new ArrayList<UploadFile>();
String sql = "select * from uploadfile";
conn = DBConnection.getConn();
pstmt = DBConnection.getPstmt(conn, sql);
rs = DBConnection.getRest(pstmt);
try {
while (rs.next()) {
UploadFile uploadFile = new UploadFile();
uploadFile.setId(rs.getInt("id"));
uploadFile.setFileUrl(rs.getString("file_Url"));
uploadFile.setStatus(rs.getInt("status"));
uploadFile_l.add(uploadFile);
}
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(rs != null){
try {
rs.close();
rs = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
if(pstmt != null){
try {
pstmt.close();
pstmt = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
if(conn != null){
try {
conn.close();
conn = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
return uploadFile_l;
}
public class ReadDB implements Runnable {
public void run() {
List<UploadFile> uploadFiles = new UploadFileDao().listUploadFile();
System.out.println(uploadFiles.size());
}
public static void main(String[] args) {
ReadDB readDB = new ReadDB();
while (true) {
readDB.run();
try {
Thread.sleep(5000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
}
}
运行的时候报
com.mysql.jdbc.excepti**.MySQLNonTransientConnectionException: No operati** allowed after connection closed.
at com.mysql.jdbc.SQLError.createSQLException(SQLError.java:888)
at com.mysql.jdbc.Connection.checkClosed(Connection.java:1931)
at com.mysql.jdbc.Connection.prepareStatement(Connection.java:4705)
at com.mysql.jdbc.Connection.prepareStatement(Connection.java:4671)
at com.test.util.DBConnection.getPstmt(DBConnection.java:40)
at com.test.dao.UploadFileDao.listUploadFile(UploadFileDao.java:23)
at com.test.util.ReadDB.run(ReadDB.java:11)
at com.test.util.ReadDB.main(ReadDB.java:18)
Exception in thread "main" java.lang.NullPointerException
at com.test.util.DBConnection.getRest(DBConnection.java:50)
at com.test.dao.UploadFileDao.listUploadFile(UploadFileDao.java:24)
at com.test.util.ReadDB.run(ReadDB.java:11)
at com.test.util.ReadDB.main(ReadDB.java:18)
说我的于数据库断开之后还进行数据库操作
但是如果不断开链接会导致内存泄露。。。
请问怎么解决？ java --------------------编程问答-------------------- 多线程引起的吧。
其中一个线程把conection关闭了，另外一个线程想操作这个connection自然就报错了，楼主可以仔细看，报的是空指针异常，也就是conection已经为null了，然后你对他还有操作。 --------------------编程问答-------------------- 同步一下呗！！！！
--------------------编程问答--------------------
可以使用isClose来判断一下
--------------------编程问答--------------------
yes------ --------------------编程问答-------------------- 其他不想说，我只想问一句：
readDB.run();
这个位置确定是调用run()方法的吗？这么写不是多线程的吧？ --------------------编程问答-------------------- 我数据库连接是读取properties配置文件读取的 。。
那的代码我就不粘贴了
下面是DBConnection的数据库连接类
public class DBConnection {
private static Connection conn = null;
private static final String filePath = "jdbc.properties";
private DBConnection() {
ReadProp readProp = new ReadProp(filePath);
String driver = readProp.retVal("driver");
String url = readProp.retVal("url");
String user = readProp.retVal("user");
String password = readProp.retVal("password");
try {
if (conn == null) {
Class.forName(driver);
conn = DriverManager.getConnection(url, user, password);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
} catch (SQLException e) {
e.printStackTrace();
}
}
public static Connection getConn() {
if (conn == null) {
new DBConnection();
}
return conn;
}
public static PreparedStatement prepareStatement(Connection conn, String sql) {
PreparedStatement pstmt = null;
try {
pstmt = conn.prepareStatement(sql);
} catch (SQLException e) {
e.printStackTrace();
}
return pstmt;
}
public static ResultSet executeQuery(PreparedStatement pstmt) {
ResultSet rs = null;
try {
rs = pstmt.executeQuery();
} catch (SQLException e) {
e.printStackTrace();
}
return rs;
}
public static void close(Connection conn) {
if (conn != null) {
try {
conn.close();
conn = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void close(PreparedStatement pstmt) {
if (pstmt != null) {
try {
pstmt.close();
pstmt = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void close(ResultSet rs) {
if (rs != null) {
try {
rs.close();
rs = null;
} catch (SQLException e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
System.out.println(DBConnection.getConn());
}
}
Dao 层
public class UploadFileDao {
private Connection conn = null;
private PreparedStatement pstmt = null;
private ResultSet rs = null;
public List<UploadFile> listUploadFile() {
String sql = "select * from uploadfile";
conn = DBConnection.getConn();
pstmt = DBConnection.prepareStatement(conn, sql);
rs = DBConnection.executeQuery(pstmt);
List<UploadFile> uploadFile_l = new ArrayList<UploadFile>();
try {
while (rs.next()) {
UploadFile uploadFile = new UploadFile();
uploadFile.setId(rs.getInt("id"));
uploadFile.setFileUrl(rs.getString("file_Url"));
uploadFile.setStatus(rs.getInt("status"));
uploadFile_l.add(uploadFile);
}
} catch (SQLException e) {
e.printStackTrace();
} finally{
if(rs != null){
DBConnection.close(rs);
}
if(pstmt != null){
DBConnection.close(pstmt);
}
if(conn != null){
DBConnection.close(conn);
}
}
return uploadFile_l;
}
public static void main(String[] args) {
System.out.println(new UploadFileDao().listUploadFile());
}
}
Timer 层
public class Time extends TimerTask // 创建测试的类Time继承TimerTask，导入TimerTask包
{
private Timer timer = null;// 开始要将timer对象赋初值null
private long timestop = 5000;// 每隔5秒执行一次任务
public Time() {
timer = new Timer();
}
// 构造函数
private void Time() {
UploadFileDao uploadFileDao = new UploadFileDao();
List<UploadFile> uploadFile_l = uploadFileDao.listUploadFile();
for (UploadFile uploadFile : uploadFile_l) {
System.out.println(uploadFile.getFileUrl());
}
}
// 需要执行的任务，也就是定时需要执行的功能模块函数，都可以写在这个函数里面，当然函数名可以自己取。
public void test() {
Time t = new Time();
Date date = new Date();
timer.schedule(t, date, timestop);
}
// 真正启动任务的函数，当在main函数中new一个新对象时，调用此函数，在此函数中有schedule方法，启动任务。
public void run() {
this.Time();
}
public static void main(String[] args) {
Time t = new Time();// 创建对象实体
t.test();// 启动定时器任务
}
}
现在运行的时候还是报之前的错误，我知道是关闭了Connection后又调用了，但是现在我想定时读取数据库里的数据，必须再次调用啊。 这里该怎么解决呢？ Connection总不能不关闭吧。 --------------------编程问答-------------------- 可不关啊,只使用一个连接,或者使用连接池....都是长连接的原理. --------------------编程问答--------------------
写了一个功能，每次需要执行的时候才启动程序，用的是数据库连接池 。
我也不知道程序在哪里结束，
所以： 如何根据程序的结束来释放连接池里面的连接呢 --------------------编程问答-------------------- DBConnection
public static Connection getConn() {
if (conn == null) {
conn=new DBConnection();
}
return conn;
} --------------------编程问答--------------------
if(rs != null){
try {
rs.close();
rs = null;
} catch (SQLException e) {
e.printStackTrace();
}rs = null;这条语句不要试试
补充：Java , Java SE
