如何用GridBagLayout实现BoxLayout式的组件垂直居中？

我想通过GridBagLayout实现类似BoxLayout中Box.createVerticalGlue()的组件垂直居中效果。最初采用垂直Box布局：

Box box = Box.createVerticalBox();
box.add(Box.createVerticalGlue());
box.add(add);
box.add(remove);
box.add(edit);
box.add(Box.createVerticalGlue());

JPanel internalPanel = new JPanel(new BorderLayout());
internalPanel.add(keywordsScrollPane, BorderLayout.CENTER);
internalPanel.add(box, BorderLayout.EAST);

但按钮尺寸不一致导致布局混乱。改用GridBagLayout后，通过GridBagConstraints.fill解决了按钮宽度统一的问题，却无法实现组件垂直居中：调整网格行、GridBagConstraints.anchor和GridBagConstraints.weightY后，按钮间距过大。我希望按钮能像Box布局那样紧凑分组并垂直居中，如何用GridBagLayout实现？我使用了自定义的ConstraintsBuilder类，相关代码如下：

public class KeywordsDialog extends JDialog implements ActionListener, ListSelectionListener {

    private JList<String> keywords;
    private JScrollPane keywordsScrollPane;
    private JButton add;
    private JButton remove;
    private JButton edit;

    private Set<String> keywordsList;

    public KeywordsDialog(Window parent, Collection<String> keywordsList) {
        super(parent);

        this.keywordsList = keywordsList == null ? new HashSet<String>() : new HashSet<String>(keywordsList);
        if (keywordsList != null && !keywordsList.isEmpty()) {
            this.keywords = new JList<String>(toListModel(keywordsList));
        } else {
            this.keywords = new JList<String>(new DefaultListModel<String>());
        }
        this.keywordsScrollPane = new JScrollPane(keywords);

        this.add = new JButton("Add");
        this.remove = new JButton("Remove");
        this.edit = new JButton("Edit");

        this.edit.setEnabled(false);
        this.add.setEnabled(false);

        ConstraintsBuilder builder = LayoutUtils.gridBagConstraintsBuilder();
        JPanel internalPanel = new JPanel(new GridBagLayout());
        internalPanel.add(this.keywordsScrollPane, builder.gridX(0).gridY(0).gridHeight(3).margins(0, 0, 0, 5)
                .fill(GridBagConstraints.BOTH).weightX(1D).weightY(1D).build());
        internalPanel.add(this.add,
                builder.reset().gridX(1).gridY(0).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(1D).build());
        internalPanel.add(this.remove,
                builder.reset().gridX(1).gridY(1).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(1D).build());
        internalPanel.add(this.edit,
                builder.reset().gridX(1).gridY(2).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(1D).build());

        this.keywords.setBorder(BorderFactory.createTitledBorder("Keywords"));
        internalPanel.setBorder(BorderFactory.createEmptyBorder(10, 10, 10, 10));

        this.setLayout(new BorderLayout());
        this.add(internalPanel, BorderLayout.CENTER);

        Dimension screen = GuiHelper.getScreenSize(parent);
        this.setSize((int) (screen.getWidth() / 4), (int) (screen.getHeight() / 3));
        this.setLocationRelativeTo(parent);
        this.setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    }
    // ...
}

要实现按钮紧凑分组且垂直居中，核心是调整GridBagConstraints的weightY和anchor属性，同时给按钮组上下添加占位的“弹性行”，具体修改如下：

ConstraintsBuilder builder = LayoutUtils.gridBagConstraintsBuilder();
JPanel internalPanel = new JPanel(new GridBagLayout());

// 左侧列表，占据所有垂直空间
internalPanel.add(this.keywordsScrollPane, builder.gridX(0).gridY(1).gridHeight(3).margins(0, 0, 0, 5)
        .fill(GridBagConstraints.BOTH).weightX(1D).weightY(1D).build());

// 顶部占位行，占据上方剩余垂直空间
internalPanel.add(Box.createGlue(), builder.reset().gridX(1).gridY(0).fill(GridBagConstraints.VERTICAL)
        .weightX(1D).weightY(1D).build());

// 按钮设置：weightY设为0，保持紧凑排列
internalPanel.add(this.add,
        builder.reset().gridX(1).gridY(1).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(0D).anchor(GridBagConstraints.CENTER).build());
internalPanel.add(this.remove,
        builder.reset().gridX(1).gridY(2).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(0D).anchor(GridBagConstraints.CENTER).build());
internalPanel.add(this.edit,
        builder.reset().gridX(1).gridY(3).fill(GridBagConstraints.HORIZONTAL).weightX(1D).weightY(0D).anchor(GridBagConstraints.CENTER).build());

// 底部占位行，占据下方剩余垂直空间
internalPanel.add(Box.createGlue(), builder.reset().gridX(1).gridY(4).fill(GridBagConstraints.VERTICAL)
        .weightX(1D).weightY(1D).build());

关键调整说明 #

• 占位行：用Box.createGlue()作为占位组件，设置fill(VERTICAL)和weightY(1D)，让它们自动占据上下的剩余垂直空间，将按钮组挤压到容器垂直中间位置，逻辑和BoxLayout的VerticalGlue完全一致。
• 按钮的weightY(0D)：告诉布局管理器不要给按钮分配额外垂直空间，按钮会保持自身的最佳尺寸，彼此紧凑排列，不会被拉伸导致间距过大。
• anchor(CENTER)：确保按钮在单元格内垂直居中，避免因单元格高度变化导致按钮偏移。

内容的提问来源于stack exchange，提问作者Cardinal System