php小编鱼仔为您带来最新的java问答：sql连接关闭而不提示。在开发过程中经常会遇到sql连接未关闭而不提示的问题，这可能会导致资源泄露和性能问题。本文将为您详细解答这一问题，并提供解决方案，帮助您更好地处理sql连接关闭的相关情况。让我们一起来了解吧！
问题内容
当尝试依次运行两个 sql 查询时（如 dbtest2 中所示），系统会返回一条错误，指出 sql 连接已关闭，即使尚未提示这样做。
到目前为止，我已尝试将 sqlconn 连接移动到不同的位置，以及按方法单独打开和关闭连接。如果只调用一个 sql 查询，系统就会按预期工作。这些是类：
import java.sql.*;
public class mysqlconnect {
private static final string db_url = "jdbc:mysql://dbconnectionurl";
private static final string user = "username";
private static final string password = "pass";
private static connection mysqlconn;
static {
try {
class.forname("com.mysql.cj.jdbc.driver");
mysqlconn = drivermanager.getconnection(db_url, user, password);
system.out.println("mysql db connection is successful");
} catch (classnotfoundexception | sqlexception e) {
e.printstacktrace(); // handle classnotfoundexception and sqlexception
}
}
public static connection getmysqlconnection() {
return mysqlconn;
}
public static void closeconnection() {
if (mysqlconn != null) {
try {
mysqlconn.close();
system.out.println("mysql db connection is closed");
} catch (sqlexception e) {
e.printstacktrace();
}
}
}
}
import java.sql.*;
import java.util.arraylist;
public class sqlquery {
private int userid;
private string password;
private boolean activated;
private string usertype;
connection sqlconn = mysqlconnect.getmysqlconnection(); // i want to be able to try accept this but idk how
public string sqlsearch(string tbname){ // all
string sqlquery = "";
if(tbname == ""){
throw new illegalargumentexception("criteria cannot be empty");
}
sqlquery = "select * from " + tbname + ";";
if(sqlquery == ""){
throw new illegalargumentexception("sql query not set, something gone wrong");
}
arraylist<string> resultlist = new arraylist<string>();
try (connection connection = sqlconn;
preparedstatement ps = connection.preparestatement(sqlquery);
resultset rs = ps.executequery()) {
resultsetmetadata metadata = rs.getmetadata();
int columncount = metadata.getcolumncount();
if (rs.next()) {
for (int i = 1; i <= columncount; i++) {
string columnvalue = rs.getstring(i);
resultlist.add(columnvalue);
}
} else {
system.out.println("no match for " + tbname);
}
} catch (sqlexception e) {
system.err.println("error executing sql query: " + e.getmessage());
e.printstacktrace();
}
string result = string.join(", ", resultlist);
return result;
}
}
public class dbtest2 {
public class main {
public static void main(string[] args) {
person person = new person(2, "password123", true, "student");
system.out.println(person.sqlsearch("course"));
system.out.println(person.sqlsearch("student"));
}
}
}
尽管付出了一切努力，我最终收到的错误消息是：
MySQL Db Connection is successful
CS101, CSC 101, Intro to Computer Science, 3
Error executing SQL query: No operations allowed after connection closed.
java.sql.SQLNonTransientConnectionException: No operations allowed after connection closed.
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:111)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:98)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:90)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:64)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:74)
at com.mysql.cj.jdbc.exceptions.SQLExceptionsMapping.translateException(SQLExceptionsMapping.java:73)
at com.mysql.cj.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:1610)
at com.mysql.cj.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:1524)
at Person.sqlSearch(Person.java:245)
at dBtest2$Main.main(dBtest2.java:8)
Caused by: com.mysql.cj.exceptions.ConnectionIsClosedException: No operations allowed after connection closed.
at java.base/jdk.internal.reflect.DirectConstructorHandleAccessor.newInstance(DirectConstructorHandleAccessor.java:62)
at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:502)
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:486)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:61)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:104)
at com.mysql.cj.exceptions.ExceptionFactory.createException(ExceptionFactory.java:149)
at com.mysql.cj.NativeSession.checkClosed(NativeSession.java:756)
at com.mysql.cj.jdbc.ConnectionImpl.checkClosed(ConnectionImpl.java:556)
at com.mysql.cj.jdbc.ConnectionImpl.prepareStatement(ConnectionImpl.java:1539)
... 3 more
期望的结果是输出只是列表
解决方法
那是因为您正在使用尝试资源。请参阅 https://www.php.cn/link/533a7de111ee3af214eee5e09e3fa1bc 了解更多详情。
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这意味着当您将连接放入 try 块中时。 try 块执行后连接关闭：
try (connection connection = sqlconn;
preparedstatement ps = connection.preparestatement(sqlquery);
resultset rs = ps.executequery()) {
只需尝试将连接移到 try 块之外，如下所示：
Connection connection = sqlConn;
try (PreparedStatement ps = connection.prepareStatement(sqlQuery);
ResultSet rs = ps.executeQuery()) {
执行完所有查询后，不要忘记关闭连接。
请注意，另一个选项是每次打开一个新连接。
