I'm a .net developer that would like to try develop some simple apps in Java. I would like to know how to do databinding in Java.
How can I show a query result in a JTable?
GustlyWind's comment is the best place to look on how to use a JTable. The key for the data is getting the items in a model. You can use the DefaultTableModel which would require that your table results are put into a 2D Array or Vector. Or you could implement your own model that uses other custom objects from your application or a different underlying data structure.
Either way, as you loop through the ResultSet of your query you are going to have to pull the relevant data and stick it in some sort of Collection.
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I am writing a desktop application in Java and it uses two JTables as the main output.
I have a working version of the program where I use DefaultTableModels to manage the underlying data of the JTables and I use an ArrayList to store the data in each model.
However, I've come across the ResultSetTableModel which stores the data in a ResultSet and a ResultSetMetaData object to implement the TableModel methods.
But I am not clear on the benefits of using a ResultSetTableModel as opposed to a DefaultTableModel or AbstractTableModel. I have searched and I cannot find any discussion on this.
Does anyone know why one would favor a ResultSetTableModel over the other options?
if you use DefaultTableModel you have to store the data into model manually, and if you ResultSetTableModel data automatically loads into JTable this is the difference.
I have a file and i read data from this and put them in a jTable. The problem is that when the file has many data (e.g 300.000 rows), my application needs a lot of memory (350MB). Is there any efficient way in order to load many rows in a JTable?
I created a Default Model and a Jtable like that:
DefaultTableModel model = new DefaultTableModel(array, colNames);
JTable data_table = new JTable();
data_table.setModel(model);
The array 'array' contains the data and the array 'colNames' the names of the Columns.
Use an embedded database, and store only the record ID in the model and then only if you need to filter/sort rows.
Absent enough information to offer a particular solution, you may be able to identify a reasonable partition function for your data's primary key, e.g. a String prefix or a Date range. Use an adjacent control to update the TableModel based on the selection. In this example, buttons are used to change a chart's data model. To minimize latency, Use SwingWorker. Aside from the memory problem, you may want to filter the table or load the file into an in-memory database such as H2 Database.
If you want to reduce the memory consuption of your program.
You could use java.nio.channels.FileChannel and map parts of the file to your main memory.
But you would have to reload/change current mapping, depending on your view.
Take a look at the javadoc of the map method.
I don' know what exactly your file is, but if you just use it as a simplistic replacement for an actual database. You're better off with using a real one.
I intend to write an JFX-Application that displays data from database tables that contain up to 1M entries. Unfortunately, the standard API makes it difficult to support lazy loading. Reading the whole table is not an option (even though it performs well up to 100K entries).
Paging can be accomplished using a custom list class provided as model to the TableView. However, I also need to control the sorting behaviour of the TableView, since in my case, this would be left to the dbms.
An ugly solution is to make the columns unsortable, and add a Click-Event listener to the Column-Header. Apart from the coding, this also makes it impossible to display the current sort order in the usual way.
It is possible to listen to a change to columnSortOrder, but the standard sorting mechanism is still applied. What I would like to be able to do is display the standard ascending/descending icon in the column header while having full control of the sort behaviour of the TableView.
[Edit: In short, I want to implement lazy loading. I want a TableView that behaves exactly like normal TableView but does not sort the list when the user clicks on a column header. However, the sort order should still be displayed in the column header label.]
Is that somehow possible to achieve?
Many thanks for your answers in advance!
For reference:
This has been added to JavaFX-8. One can use TableView.setSortPolicy(...) to customize sorting.
What's the best way to store data retrieved from database in to Java for processing?
Here's some context:
Every month, data from Excel files are stored in the database and our web application (plain JSP/Servlet) does some processing on those data in the database. Currently we use an ArrayList of Hashmaps to store data retrieved from the tables but it seems very clunky. Is there a better way or data structure to do this?
It's not really possible to create some sort of a Model class for each of these because there's no logical "User" object or anything like that. It's basically chunks of random data that need to be processed. Stored procedure is not an answer as well because the processing logic is quite complicated.
Try using Java API's to get faster execution.
Apache POI
Java Excel API namely JXL
Check the link of sample tutorial using JXL: Link
If your excel files are in csv format then use openCSV.
It's not really possible to create some sort of a Model class for each of these because there's no logical "User" object or anything like that. It's basically chunks of random data that need to be processed. Stored procedure is not an answer as well because the processing logic is quite complicated.
Then there is not really a better way than using a List<Map<String, Object>>. To soften the pain, you could abstract the Map<String, Object> away by extending it to another class e.g. Row with eventually convenience methods to cast the values (.getAsDouble(columnname) or even T get(columnname, Class<T> type), etc) so that it makes traversing and manipulating less scary.
How do I enable JTable icons and behaviors for sorting table rows by a column, without letting it use a comparison predicate to do the sorting? That is to say, how do I tell the table headers to show the arrow for ascending/descending sort order in the column being used, and get it to call appropriate methods when sort order/column change?
I am trying to create an (editable, filterable, sortable) JTable backed by an SQL query or view. The rows may not fit in memory, and may not map cleanly to java objects, so I want to do all sorting/filtering within SQL. I have already written the code for changing a query to accommodate sorting by column, filtering by values, and visible columns.
To use this, I am planning to write a JTableModel based on a ResultSet with TYPE_SCROLL_SENSITIVE, and CONCUR_UPDATABLE, so changes to the DB get propagated to the ResultSet. I will periodically (several times a second) force a refresh of the visible JTable from the ResultSet, so changes to the database become visible to the user. User changes to the table will be passed to the updateable ResultSet after validation.
I've looked a little bit at how sorting is done normally, but most implementations seems to rely on the JTable creating a javax.swing.RowSorter with a Comparator predicate, or on maintaining a sorted list of rows that fires events when changed. So, my questions:
ORM frameworks are NOT an answer to this question, because the data do not map well to entity objects. Also, the DBMS I am using is H2.
EDIT: Sortable JTable libraries based on applying Comparators or sorting predicates to row objects are also unsuitable, unfortunately. I do not believe I will be able to hold all objects in memory in order to perform sorting. This problem prevents me from using the SwingX JXTables, GlazedLists, or similar libraries. I wish I could, but I can't. Period.
** I will be dealing with many thousand rows, potentially millions, with numerous columns. Yes, I really DO need to use SQL to do the sorting and filtering.**
Questions: (in descending importance)
How do I show indicators for which column is used to sort rows?
How do I get the JTable to fire appropriate events when the column headers are LEFT-clicked to change sort order?
Is there an easier way to force the JTable to update when the database changes?
Is there a library that would make all this considerably easier (connecting DB queries or views and JTables)?
Am I going to run into horrible, horrible problems when I design the system like this?
I have never used it myself but JIDE Data Grids provides a DatabaseTableModel that provides filtering and sorting support using SQL WHERE and ORDER BY.
In answer to 1 and 2, check out SwingX, which already includes a table class with built-in sorting (and filtering). You may be able to adapt this.
Am I going to run into horrible, horrible problems when I design the system like this?
From experience, yes. I worked on a project almost exactly the same as this, where someone had designed a JTable that supposedly 'magically' bound to a database table. This coupled display logic and database access together in one big horrible mess, which we replaced entirely with reflection-driven table models and separate record CRUD operations.
You say that ORM is not the answer...
If the format of the data doesn't change, then it's worth considering anyway. Your 'entity' classes need not represent real-world entities.
If (as I suspect) your entity format changes, it might be worth considering:
A flexible map-based Record class which stores records as key-value pairs;
Dynamically-built table models for your display logic, built by querying record keys, plugged into SwingX tables to get sort and filter for free;
A similarly-designed Repository class which encapsulates your database access separately from the table itself, responsible for loading and saving Records. This acts as an adapter between your updateable ResultSet and the view (although I'd check whether using a ResultSet this way is going to require an open database connection whilst data is visible...).
This separation into 'a table that displays and sorts records' and 'a repository that manages the data' means:
You can reuse the table for non-database-bound data;
You can display database-bound records in things other than tables;
You won't go mad trying to build and test the thing :)
You should be able to subclass javax.swing.RowSorter in order to create a row sorter that does the sorting in the database. From the API docs:
"RowSorter implementations typically don't have a one-to-one mapping with the underlying model, but they can. For example, if a database does the sorting, toggleSortOrder might call through to the database (on a background thread), and override the mapping methods to return the argument that is passed in."
http://docs.oracle.com/javase/6/docs/api/javax/swing/RowSorter.html
Leaving aside the database stuff there's a class called SortableTable that's a part of JIDE Grids. It displays the sorting with a little ^ or v in the table header, and supports sorting by more than 1 column (1v, 2v, etc.).