Develop Reference

Returning a ResultSet to another function [duplicate]

This question already has answers here:
Returning a ResultSet
(8 answers)
Closed 2 years ago.
I'm working on creating a program to manage a MySQL server. I have a working UI and code that can add new entries to the database as it should. Pictured below is the proto GUI that I'm using, the part that's important for the question is the table box that will show the entries of the database when it's working.
The code that I have for reading the contents of the database works as it should. The program is structured so that I have separate classes for the interface, scene controller and SQL commands. The issue that I'm dealing with is that I can pull the needed data from the database but getting to the scene controller class to write it to the database simply isn't working.
The relevant pieces of code are included below is included below.
SQL functions:
public ResultSet readDataBase() throws Exception{
try {
// Establish connection to server
Class.forName("com.mysql.cj.jdbc.Driver");
connect=DriverManager.getConnection("jdbc:mysql://localhost/library?"+"user=tempUser&password=12345");
statement=connect.createStatement();
// Execute query and write the results
resultSet=statement.executeQuery("select * from library.books");
return resultSet;
// writeResultSet(resultSet);
} catch (Exception e){
throw e;
} finally {
close();
}
}
Scene controller code:
public void fillTable() throws SQLException{
ResultSet resultSet=null;
try {
resultSet=commands.readDataBase();
while(resultSet.next()) {
String title = resultSet.getString("title");
String author = resultSet.getString("author");
String genre = resultSet.getString("genre");
String format = resultSet.getString("format");
String isbn = resultSet.getString("isbn");
System.out.println("Title: " + title);
System.out.println("Author: " + author);
System.out.println("Genre: " + genre);
System.out.println("Format: " + format);
System.out.println("ISBN: " + isbn);
System.out.println();
}
}catch (Exception e){
e.printStackTrace();
}
}
The purpose of the code in the scene controller block is simply to test for and read the result set for now. The code for writing to write the data from the result to their respective tables will be added later. This code was selected because I originally had it in the SQL functions class and it worked there, so I knew the code was good and did its job.
Whenever I run the code however, I get this error result.
java.sql.SQLException: Operation not allowed after ResultSet closed
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:129)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:97)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:89)
at com.mysql.cj.jdbc.exceptions.SQLError.createSQLException(SQLError.java:63)
at com.mysql.cj.jdbc.result.ResultSetImpl.checkClosed(ResultSetImpl.java:445)
at com.mysql.cj.jdbc.result.ResultSetImpl.next(ResultSetImpl.java:1726)
at library.test.windows.interfaceSceneController.fillTable(interfaceSceneController.java:108)
at library.test.windows.winInterface.main(winInterface.java:33)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplicationWithArgs(LauncherImpl.java:464)
at javafx.graphics/com.sun.javafx.application.LauncherImpl.launchApplication(LauncherImpl.java:363)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.base/java.lang.reflect.Method.invoke(Method.java:564)
at java.base/sun.launcher.LauncherHelper$FXHelper.main(LauncherHelper.java:1051)
I've done some reading into this prior but the only really relevant source of info I could find was in this post from over seven years ago. The answer for that question made reference to using JavaBeans as a place to put the information as an in-between but then used a class called a 'Biler' in their sample code. I can't find any reference to a Biler anywhere except his post and my IDE (IntelliJ if that's relevant) did not recognize it at all. I've been doing some experimentation with JavaBeans but I'm not sure it solving my problem.
In summary, my question is this. What do I need to do in order to properly pass a ResultSet from the function accessing the SQL server to the class containing the code for writing it to the table in my interface? I know this must be possible somehow but I can't seem to figure it out.

Your database access code should be kept entirely separate from your user-interface code. The UI should not deal with an active ResultSet.
You need to copy the data out of the result set, or use a utility to do so for you.
CachedRowSet
A RowSet may be the solution. This interface extends ResultSet. See the Java Tutorials by Oracle for explanations.
You could use the CachedRowSet interface that keeps a copy of the result set data in memory, detached from the database. Oracle provides an implementation, as might other vendors such as your JDBC driver.
A CachedRowSet implementation is disconnected from the database. In contrast, a ResultSet maintains a database connection (the root of your problem). To quote the Javadoc:
A CachedRowSet object is a container for rows of data that caches its rows in memory, which makes it possible to operate without always being connected to its data source. Further, it is a JavaBeans™ component and is scrollable, updatable, and serializable.
That interface is extended by a few more interfaces.
POJOs
Plain old Java objects is another option, copying every field of every row from your ResultSet into properties of a Java object.
You can simply loop the result set while instantiating records. Or you can use any of a variety of frameworks to assist.
Records
Defining a class for such POJOs is much simpler when using the new records feature arriving in Java 16, now previewed in Java 15. The constructor, getters, toString, and equals & hashCode are all synthesized by the compiler. You simply declare the properties.
A record can be declared as a stand-alone class, or as a nested class, or even locally within a method.

Well, I assume you are closing the conneciton in your close() method. So that's why it is closed. The finally is executed after the method body but before the result is passed to the calling funtion.
try {
return resultSet;
} finally {
close();
}
IMHO it is a bad pratice to pass back a resultset anyway because the resultset is not really typesafe. If you change the query you will break the fillTable() function without noticing. And, of course, you would need to find a way to close the resultset and the underlying DB connection at some point. This might be challenging.

Differentiate 'Could not allocate space for object' Exception

I am getting
com.microsoft.sqlserver.jdbc.SQLServerException: Could not allocate space for object
as filegroup is full.
I want a way to identify this SQL exception from other SQL Exceptions.
If I check java.sql.SQLException.venderCode == 1105 will that be enough?And is there any place I can get the description of the 1105 code?

If I check java.sql.SQLException.venderCode == 1105 will that be enough?
Yes, that vendor code (available by calling getErrorCode()) will always map to that error. Just bear in mind it's specific to SQL Server rather than consistent across all SQL implementations.
Various sites like this one detail all the error codes available for SQL server (including 1105.)

Checking the error code alone is sufficient for your need. The returned vendorCode is the SQL Server error number. SQL Server errors and the tokenized message text can be retrieved by the sys.messages DMV. Example for the US English language:
SELECT *
FROM sys.messages
WHERE
message_id = 1105
AND language_id = 1033;

How to find data which is causing Oracle JDBC: underflow in double

I am getting following error
Caused by: java.lang.IllegalArgumentException: Underflow
at oracle.jdbc.driver.OraclePreparedStatement.setDoubleInternal(OraclePreparedStatement.java:6604)
~[ojdbc7-12.1.0.2.0-p0.jar:12.1.0.2.0]
at oracle.jdbc.driver.OraclePreparedStatement.setDouble(OraclePreparedStatement.java:6574)
~[ojdbc7-12.1.0.2.0-p0.jar:12.1.0.2.0]*
This happens when one of the double value in my data object is null/illegal. This happens when session.flush being called. The problem is my data object have composition of other data object and N number of collection elements.
It's difficult to find which double data member is giving the issue.
I have enabled the persistence log and not able to see the query being formed for update statement.
Don't have anything on log except the above line. I have put breakpoints on all the get member functions. The exception didnt happen when session.update is getting called. It happens when session.flush being called. Also sometimes I get session time out as I have huge number of data elements. So debugging all the data elements was bit difficult.
How to find which member is giving the issue ?

Do you use something like Hibernate? You could enable debug or trace log to show the sql-statements that are generated.
It turns out even Oracle JDBC has log that can be enabled:
From https://stackoverflow.com/a/40491028/66207 :
Place the trace-enabled ojdbc jar file in your classpath. Quote from
the linked Oracle page: "To get log output, you must use the debug
JAR files, which are indicated with a "_g" in the file name, like
ojdbc5_g.jar or ojdbc6_g.jar." My Oracle 11g installation contained
Create a logging.properties file as described on the linked Oracle
page, and adjust the logging levels to your needs. Example:
.level=SEVERE oracle.jdbc.level=FINEST
oracle.jdbc.handlers=java.util.logging.FileHandler
java.util.logging.FileHandler.level=FINEST
java.util.logging.FileHandler.pattern=jdbc.log
java.util.logging.FileHandler.count=1
java.util.logging.FileHandler.formatter=java.util.logging.SimpleFormatter
Add the JVM properties "-Doracle.jdbc.Trace=true
-Djava.util.logging.config.file=logging.properties" to the java startup command for your JDBC application.
The JDBC application should now produce a file named jdbc.log which should contain the desired information. In some cases it can be necessary to specify the full path to the logging.properties file.
Or the Hibernate Solution from https://stackoverflow.com/a/1713464/66207 :
You need to enable [logging][2] for the the following categories:
org.hibernate.SQL - set to debug to log all SQL DML statements as they are executed
org.hibernate.type - set to trace to log all JDBC parameters
So a log4j configuration could look like:
# logs the SQL statements
log4j.logger.org.hibernate.SQL=debug
# Logs the JDBC parameters passed to a query
log4j.logger.org.hibernate.type=trace
The first is equivalent to hibernate.show_sql=true legacy [property][1], the second prints the bound parameters among other things.

I was able to print the persistence log after enabling the following property :
sessionFactory-> cacheAccess->SessionFactory->jdbcservices->sqlStatementLogger->logToStdOut --> set this to TRUE.
Now the logs were printed and I was able to see the data which was causing the issue.

Java and MySQL query

I have problem with java and MySQL. My code:
Connection connection;
// ...
for (String query : updateAndInsertQuery) {
Statement stm = connection.createStatement();
stm.execute(query);
stm.close();
}
Statement stm2 = connection.createStatement();
System.out.println("Before query");
System.out.flush();
ResultSet Result = stm2.executeQuery(selectQuery);
System.out.println("After query");
System.out.flush();
int vfrom, vto;
while (Result.next()) {
// ...
}
When I run program i see in MySQL queries and run
show processlist;
selectQuery is visible on list wth status Sending data or Writing to net. On console print: Before query. Next
show processlist;
returns empty list, but application don't print After query. Do you have similar problem?
-- edit
I resolve my problem.
I think:
wen MySQL returns data and query isn't visible on processlist in MySQL
I should immediately get on console message: After query
but console was empty, java process works (cpu usage was 90-100%) so I think it was my mistake, but after 1h application throws Exception
Increase memory limit resolve my problem.
So I have next question why application throw exception after hour? Garbage collection try dealocate unised objects?

executing queries manually usually leads into many different problems - all of which are platform-specific and DB-specific. I think your best answer will be : "switch to ORM".
This framework has proven to be exceptionally good, wrappig all your SQL-data into Entities and transactions (if required) will resolve most of your problems at the same time - you will only need to annotate your entities and relationships correctly. Database-queries can be executed via JPA-"criteria"s which are platform-independent AND allow you to avoid a lot of problems as well as making your code READABLE.
Tutorial : http://www.vogella.com/tutorials/JavaPersistenceAPI/article.html
SO-question : https://stackoverflow.com/questions/743065/what-is-the-fastest-way-to-learn-jpa
With JPA, you wont need to care about statements or queries anymore (well, at least most of the time) and your mentioned problem will disappear - PLUS : it only takes 30-60min to implement.
Additional tip : use Maven & Eclipselink (JPA2 implementation) - thats a very powerful, portable combination

Check if there is an error in update/insert | MongoDB Java driver

I want to check if an insert fails (due to unique=True index in the collection). If there is an error do something. Bellow is an example of my code.
DBCollection user...;
BasicDBObject Doc = new BasicDBObject(... );
String user_exists = user.insert(Doc).getError(); //insert the doc get error if any
if(user_exists!=null){ //any errors?
user.update(new BasicDBObject(...)); // error exists so do smthng
}
The above as it is does not work. I believe that the String user_exists is always null. How can I make the above work?
I have seen similar SO questions and mention the WriteConcern which can be passed in the insert(). E.g.
coll.insert(dbObj, WriteConcern.SAFE);
sources: SO question
or
Mongo docs
However I do not know which one field should I pass (SAFE, ACKNOWLEDGED, UNACKNOWLEDGED etc..) in order to get the error. Maybe I'm pointed in the wrong direction.
I do not wish to raise an exception just to check if there is an error returned by the insert operation.

If you are using WriteConcern.ACKNOWLEDGED (which I think is also SAFE) you don't need to pollute your code with error checking.
For ACKNOWLEDGED, the driver will automatically issue a getLastError command automatically and raise an exception if anything got wrong, for example duplicate index violation.
Starting from v2.10 of the Java Driver, the default Write Concern is ACKNOWLEDGED
EDIT
I do not wish to raise an exception just to check if there is an error returned by the insert operation.
You shouldn't do this, but in any case:
The insert method indeed returns WriteResult. If it's getError() is null, everything is OK, otherwise it returns something such as E11000 duplicate key error index:.... For this to work, you will have to use WriteConcern.UNACKNOWLEDGED