如何使用 JDBC 数据源在 JavaFX 中构建多级 TreeView？

Question

In my JavaFX program I want to dynamically generate a tree using the live data set from my database (I'm using MariaDB, but it could be any SQL database).

I had searched a bunch and could not find a direct answer to my question, so I spent some time learning how JDBC ResultSet 's work, how the next() method works, and how while loops work. A few trial-and-error attempts finally led me to the result I wanted, so I thought I would share it in case anyone else finds themselves in my position.

See my answer below.

Answer 1

edit It seems I've designed the overall program poorly in not using threading to isolate the GUI from the JDBC query. I think this can be fixed using JavaFX concurrency, but I've never used it so until I can update the code below, just ignore the stuff outside the while loop.

Firstly, I'm using following versions of MariaDB (10.4.12), Java (13.0.2.8), JavaFX (13.0.2), and MariaDB JDBC (2.6.0). I don't think any of this will make a difference, but just in case.. I'm using FXML, which is why you won't see any UI formatting in there anywhere.

This is the full method that generates the TreeView in my JavaFX program. It's then called from a separate class shortly after generating the Stage and Scene objects.

They key part is the while loop, which was a struggle for me to get right. I initially thought I needed a nested while(rs.next()) loop, but then I realised that this was causing rows to be skipped because each rs.next() call is related to the previous one, not to the while loop in which it is used.

Note also that the SQL statement is important. If the statement gives results out of order the method doesn't work correctly.

    public void generateTree(DataSource dataSource) {

        source = null;
        this.source = dataSource;

        Connection con = null;
        Statement stmt = null;

        TreeItem<String> rootTreeItem = new TreeItem<String>("EMT");
        rootTreeItem.setExpanded(true);
        emtTree.setRoot(rootTreeItem);

        TreeItem<String> site = null;
        TreeItem<String> plant = null;

        try {
            con = source.getConnection();
            try {
                stmt = con.createStatement();
                ResultSet rs = stmt.executeQuery("SELECT sites.siteid, sites.longname, plants.plantid, plants.siteplantid, plants.shortname FROM sites INNER JOIN plants ON plants.siteid=sites.siteid ORDER BY sites.longname ASC, plants.siteplantid ASC");

                String site1 = "";  //It's not possible for the site name to be "" in the result set because the database design prevents it.

                //Steps through the result set from first row item to last row item.
                while(rs.next()) {

                    //This bit prevents repeating the same first level items multiple times.
                    //I only want each site to appear once, and under each site is a list
                    //of plants.
                    if (!site1.equals(rs.getString("sites.longname"))) {
                        site = new TreeItem<String>(rs.getString("sites.longname"));
                        rootTreeItem.getChildren().add(site);
                        site1 = rs.getString("sites.longname");
                    }

                        //This section is never skipped and will add all the plants to a given
                        //site until the next site is reached in the result set, then the if
                        //is triggered again and the process for the new site.
                        plant = new TreeItem<String>(rs.getInt("plants.siteplantid") + " " + rs.getString("plants.shortname"));
                        site.getChildren().add(plant);
                }
            } catch (SQLException e) {
                System.out.println("Statement Error");
                System.err.println("SQL State: " + ((SQLException)e).getSQLState());
                System.err.println("Error Code: " + ((SQLException)e).getErrorCode());
                System.err.println("Message: " + ((SQLException)e).getMessage());
                System.err.println("Cause: " + ((SQLException)e).getCause());
                return;
            }
        } catch (SQLException e) {
            e.printStackTrace();
            return;
        } finally {
            if (stmt != null) {
                try {
                    stmt.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if (con != null) {
                try {
                    con.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
    }

I'll probably find ways to improve it in future, but for now I'm just happy to have it working. Ignore the messy exception handling - its a work in progress!

Answer 2

Here is my try how to do it with not blocking the UI Thread:

public class YourClassName {

ArrayList<ResultBean> fetchedData = null;

public void createTree() {

    // run in other thread fetching the data
    Task task = new Task<Void>() {
        @Override
        protected Void call() throws Exception {
            // show loading pane -> you can use the one from import org.controlsfx.control.MaskerPane
            // https://github.com/controlsfx/controlsfx/wiki/ControlsFX-Features
            loadingPane.setVisible(true);

            // get data
            fetchedData = generateTreeData(yourDataSource);
            return null;
        }

        @Override
        protected void succeeded() {
            // the data has been fetched, now is safe to build your tree
            super.succeeded();
            buildTreeFromTheData(fetchedData);
        }
    };
    new Thread(task).start();
  }
}

Fetch the data from your database:

public ArrayList<ResultBean> getTreeData(DataSource dataSource) {

    ArrayList<ResultBean> resultBeans = new ArrayList<>();
    source = null;
    this.source = dataSource;

    Connection con = null;
    Statement stmt = null;

    try {
        con = source.getConnection();
        try {
            stmt = con.createStatement();
            ResultSet rs = stmt.executeQuery("SELECT " +
                    "sites.siteid, " +
                    "sites.longname, " +
                    "plants.plantid, " +
                    "plants.siteplantid, " +
                    "plants.shortname " +
                    "FROM sites " +
                    "INNER JOIN plants ON plants.siteid=sites.siteid " +
                    "ORDER BY sites.longname ASC, plants.siteplantid ASC");

            while (rs.next()) {

                ResultBean resBean = new ResultBean();
                resBean.setSiteId(rs.getString("sites.siteid"));
                //....
                //....
                // set all values and add it to the result array
                resultBens.add(resBean);
            }
        } catch (SQLException e) {
            e.printStackTrace();
        }
    } catch (SQLException e) {
        e.printStackTrace();
    } finally {
        if (stmt != null) {
            try {
                stmt.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
        if (con != null) {
            try {
                con.close();
            } catch (SQLException e) {
                e.printStackTrace();
            }
        }
    }

    return resultBens;
}

ResultBean:

public class ResultBean {
    private int siteid;
    private String longname;
    private int plantid;
    private int siteplantid;
    private String shortname;

    // setters
    ....
    // getters
    ....
}

And finally, build the tree with your logic:

    public void buildTreeFromTheData(ArrayList<ResultBean> treeData) {

    // do you logic here, loop over treeData ArrayList in while loop
    TreeItem<String> rootTreeItem = new TreeItem<String>("EMT");
    rootTreeItem.setExpanded(true);
    emtTree.setRoot(rootTreeItem);

    TreeItem<String> site = null;
    TreeItem<String> plant = null;

    //This bit prevents repeating the same first level items multiple times.
    //I only want each site to appear once, and under each site is a list
    //of plants.
    //if (!site1.equals(rs.getString("sites.longname"))) {
    //    site = new TreeItem<String>(rs.getString("sites.longname"));
    //    rootTreeItem.getChildren().add(site);
    //    site1 = rs.getString("sites.longname");
   // }

    //This section is never skipped and will add all the plants to a given
    //site until the next site is reached in the result set, then the if
    //is triggered again and the process for the new site.
    // plant = new TreeItem<String>(rs.getInt("plants.siteplantid") + " " + rs.getString("plants.shortname"));
    // site.getChildren().add(plant);

   // finally, hide the loading pane
   maskerPane.setVisible(false);
}