我制作了一个 JTable，其中填充了我数据库中的数据。它从文本字段中获取数据并将它们添加到表和数据库中。关键是我有一个删除按钮，我可以用它从表本身中删除选定的行(使用 defaultTableModel)，但它不会从实际数据库中删除该数据。当我再次运行该程序时，已删除的行再次位于 JTable 中。
这可能会变得困惑，但希望有人能弄清楚我遗漏了什么。帮助将不胜感激，但不要，我的时间不多了，无法完全检修我的系统部分(尽管我认为这不是必要的，考虑到添加按钮的工作)
抱歉所有代码，不确定哪些位有用，哪些位没用，我认为最有用的是添加和删除按钮，它们位于底部，'updateReview' 方法上方。
public class MovieReviewSystem extends JFrame {
/**
* TODO: This method should construct a new MovieReviewSystem window and populate it using the MovieReviewDSC.
* Before displaying anything, this class should ask the user whether to load *everything* or just
* the 'useful' reviews.
*/
// Main method to run the class
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
@Override
public void run() {
new MovieReviewSystem().setVisible(true);
}
});
}
// Load data method
private Object[][] loadData()
{
List<MovieReview> movieData;
try {
movieData = MovieReviewDSC.list();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
movieData = new ArrayList<>();
}
Object[][] data = new Object[movieData.size()][];
for (int i = 0; i < movieData.size(); ++i)
{
MovieReview temp = movieData.get(i);
data[i] = new Object[]
{
temp.getId(),
temp.getUser(),
temp.getMovie(),
temp.isFeatured(),
temp.getRating(),
temp.getHelpful(),
temp.getUnhelpful(),
temp.getComments()
};
}
return data;
}
private Object[][] data = loadData();
private String[] columnNames = {"ID", "User", "Movie", "Featured?", "Rating", "Helpful", "Unhelpful"};
private MovieReviewTableModel tableModel = new MovieReviewTableModel(data, columnNames);
JTable table = new JTable(tableModel);
public MovieReviewSystem() {
setTitle("Movie Review System");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//setMinimumSize(getSize());
setSize(540,600);
createTable();
}
private void createTable()
{
final TableRowSorter<TableModel> rowSorter = new TableRowSorter<TableModel>(tableModel);
//Overall Panel
JPanel bigPanel = new JPanel(new BorderLayout());
add(bigPanel);
// overall search Panel
JPanel searchPanel = new JPanel(new BorderLayout());
searchPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));
bigPanel.add(searchPanel, BorderLayout.NORTH);
// search field panel
JPanel searchField = new JPanel();
searchPanel.add(searchField, BorderLayout.NORTH);
// Radio buttons panel
JPanel searchRadioButtons = new JPanel();
searchPanel.add(searchRadioButtons, BorderLayout.SOUTH);
//Search
JLabel searchLB = new JLabel("Search with keywords: ");
searchField.add(searchLB);
final JTextField searchTF = new JTextField(20); // eclipse says this needs to be final, don't change
searchField.add(searchTF);
JButton searchBT = new JButton("Search");
searchField.add(searchBT);
JRadioButton allRB = new JRadioButton("All");
searchRadioButtons.add(allRB);
allRB.setSelected(true); // 'All' selected by default
JRadioButton usersRB = new JRadioButton("Users");
searchRadioButtons.add(usersRB);
JRadioButton moviesRB = new JRadioButton("Movies");
searchRadioButtons.add(moviesRB);
// Search Button
searchBT.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
String searchString = searchTF.getText();
rowSorter.setRowFilter(RowFilter.regexFilter(searchString, 2)); //Apply search on movie
}
});
// this also allows for pressing enter to search
searchTF.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
String searchString = searchTF.getText();
rowSorter.setRowFilter(RowFilter.regexFilter(searchString, 2)); //Apply search on movie
/*if(moviesRB.isSelected())
{
rowSorter.setRowFilter(RowFilter.regexFilter(searchString, 2)); //Apply search on movie
}
else if(usersRB.isSelected())
{
rowSorter.setRowFilter(RowFilter.regexFilter(searchString, 1)); //Apply search on movie
}
else
{
rowSorter.setRowFilter(RowFilter.regexFilter(searchString, 1, 2)); //Apply search on movie
}*/
}
});
// END search field and buttons
// Three buttons
JPanel threeButtonPanel = new JPanel();
bigPanel.add(threeButtonPanel);
// Show only Featured
JButton onlyFeatured = new JButton("Only show Featured");
threeButtonPanel.add(onlyFeatured);
// Show only Helpful
JButton onlyHelpful = new JButton("Only show Helpful");
threeButtonPanel.add(onlyHelpful);
// Sort by Movie then Helpfulness Button
JButton sortByMovieThenHelpfulBT = new JButton("Sort by Movie then Helpfulness");
threeButtonPanel.add(sortByMovieThenHelpfulBT);
sortByMovieThenHelpfulBT.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
RowSorter.SortKey sortMovie = new RowSorter.SortKey(2, SortOrder.ASCENDING);
RowSorter.SortKey sortHelp = new RowSorter.SortKey(5, SortOrder.DESCENDING);
ArrayList<RowSorter.SortKey> sortKeyList = new ArrayList<RowSorter.SortKey>();
sortKeyList.add(sortMovie);
sortKeyList.add(sortHelp);
rowSorter.setSortKeys(sortKeyList);
}
});
//END Three Buttons
// *** TABLE ***
setLayout(new FlowLayout());
JScrollPane scrollPane = new JScrollPane(table); // table needs to be enclosed in a scrollpane
table.setSelectionMode(ListSelectionModel.SINGLE_SELECTION); // select one row at a time
table.setPreferredScrollableViewportSize(new Dimension(500,300)); // size
//table.setFillsViewportHeight(true);
add(scrollPane);
setVisible(true);
// Row Sorter
table.setRowSorter(rowSorter);
// *** END Table ***
//Reset button -- NOT NECESSARY
JButton resetBT = new JButton("Reset sorting");
add(resetBT);
resetBT.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
rowSorter.setSortKeys(null);
}
});
// add button *********************
JButton addBT = new JButton("Add");
add(addBT);
addBT.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent e)
{
JFrame idFrame = new JFrame();
String id = JOptionPane.showInputDialog(idFrame, "Enter an ID");
ReviewEditor editor = new ReviewEditor(MovieReviewSystem.this, id);
editor.pack();
editor.setVisible(true);
}
});
// delete button ****************
JButton deleteBT = new JButton("Delete");
add(deleteBT, BorderLayout.SOUTH);
deleteBT.addActionListener(new ActionListener()
{
public void actionPerformed(ActionEvent event)
{
int row = table.getSelectedRow();
if(row != -1)
{
int result = JOptionPane.showConfirmDialog(MovieReviewSystem.this, "Are you sure?");
if (result == JOptionPane.OK_OPTION)
{
tableModel.removeRow(row);
MovieReview movieReviewDelete = new MovieReview();
movieReviewDelete.setId((String) table.getValueAt(row, 0));
movieReviewDelete.setUser((String) table.getValueAt(row, 1));
movieReviewDelete.setMovie((String) table.getValueAt(row, 2));
movieReviewDelete.setFeatured((boolean) table.getValueAt(row, 3));
movieReviewDelete.setRating((int) table.getValueAt(row, 4));
movieReviewDelete.setHelpful((int) table.getValueAt(row, 5));
movieReviewDelete.setUnhelpful((int) table.getValueAt(row, 6));
movieReviewDelete.setComments((String) table.getValueAt(row, 7));
try {
MovieReviewDSC.delete(movieReviewDelete);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
});
}
/**
* TODO This method should attempt to update a MovieReview record in the database.
* @param isUpdate A boolean to indicate if the record should be updated or created new. If true; the update method should be used.
* @param review The MovieReview object to be updated or added
* @return a boolean indicating success (true) or failure (false)
*/
public boolean updateReview(boolean isUpdate, MovieReview review) {
if (isUpdate = false)
{
try {
MovieReviewDSC.add(review);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
else
{
try {
MovieReviewDSC.edit(review);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return true;
}
}
如您所见，它们从属于此类的 MovieReviewDSC 调用添加和删除方法:
public class MovieReviewDSC {
private static Connection connection;
private static Statement statement;
private static PreparedStatement preparedStatement;
public static void connect() throws SQLException {
String url = "null"; //took this info out for obvious reasons
String user = "null";
String password = "null";
connection = DriverManager.getConnection(url, user, password);
statement = connection.createStatement();
}
public static void disconnect() throws SQLException {
if (preparedStatement != null) preparedStatement.close();
if (statement != null) statement.close();
if (connection != null) connection.close();
}
/**
* TODO: This method should find a MovieReview with the given ID in the database
* @param id The ID of the MovieReview to be found.
* @return If it exists; a MovieReview with the given ID. Otherwise null.
* @throws SQLException
*/
public static MovieReview find(String id) throws SQLException {
connect();
// Create query to find ID
String IDquery = "SELECT * FROM movie_review WHERE id = ?";
preparedStatement = connection.prepareStatement(IDquery);
preparedStatement.setString(1, id);
ResultSet rs = preparedStatement.executeQuery();
MovieReview movieReview = null; //null returned if ID doesn't exist
if (rs.next()) //if it does exist, creates new object and fills with attributes returned by query
{
movieReview = new MovieReview();
movieReview.setId(rs.getString(1));
movieReview.setUser(rs.getString(2));
movieReview.setMovie(rs.getString(3));
movieReview.setFeatured(rs.getBoolean(4));
movieReview.setRating(rs.getInt(5));
movieReview.setHelpful(rs.getInt(6));
movieReview.setUnhelpful(rs.getInt(7));
movieReview.setComments(rs.getString(8));
}
disconnect();
return movieReview;
}
/**
* TODO: This method should count the total number of MovieReviews in the database
* @return An int representing the number of MovieReviews
* @throws SQLException
*/
public static int count() throws SQLException {
connect();
String queryCount = "SELECT COUNT(*) FROM movie_review";
preparedStatement = connection.prepareStatement(queryCount);
ResultSet rs = preparedStatement.executeQuery();
MovieReview movieReview = null;
int count = 0; //set to 0 by default
if (rs.next())
{
count = rs.getInt(1); //Count will only return one column
}
disconnect();
return count;
}
/**
* TODO: This method should obtain a list of all MovieReviews from the database
* @return A list of all stored MovieReviews
* @throws SQLException
*/
public static List<MovieReview> list() throws SQLException {
connect();
String queryList = "SELECT * FROM movie_review";
preparedStatement = connection.prepareStatement(queryList);
ResultSet rs = preparedStatement.executeQuery();
ArrayList<MovieReview> movieReviewList = new ArrayList<MovieReview>();
MovieReview movieReview = null;
while(rs.next())
{
movieReview = new MovieReview();
movieReview.setId(rs.getString(1));
movieReview.setUser(rs.getString(2));
movieReview.setMovie(rs.getString(3));
movieReview.setFeatured(rs.getBoolean(4));
movieReview.setRating(rs.getInt(5));
movieReview.setHelpful(rs.getInt(6));
movieReview.setUnhelpful(rs.getInt(7));
movieReview.setComments(rs.getString(8));
movieReviewList.add(movieReview); // add to arrayList
}
return movieReviewList;
}
/**
* TODO: This method should try to add the given MovieReview to the database.
* Note: The ID of this MovieReview must be unique
* @param movieReview The MovieReview to be added
* @throws Exception If the ID of the MovieReview already exists in the database
*/
public static void add(MovieReview movieReview) throws Exception {
// set precondition that ID does not already exist
MovieReview temp = find(movieReview.getId()); // put ID in temp
boolean notExist = (temp == null); // temp should be null
if (!notExist) // If not, show error
{
String message = "The ID you are trying to add already exists.";
throw new Exception(message);
}
connect();
String insert = "INSERT INTO movie_review VALUES(?,?,?,?,?,?,?,?)";
preparedStatement = connection.prepareStatement(insert);
preparedStatement.setString(1, movieReview.getId());
preparedStatement.setString(2, movieReview.getUser());
preparedStatement.setString(3, movieReview.getMovie());
preparedStatement.setBoolean(4, movieReview.isFeatured());
preparedStatement.setInt(5, movieReview.getRating());
preparedStatement.setInt(6, movieReview.getHelpful());
preparedStatement.setInt(7, movieReview.getUnhelpful());
preparedStatement.setString(8, movieReview.getComments());
preparedStatement.executeUpdate();
disconnect();
}
/**
* TODO: This method should try to update an existing MovieReview with the details of the given MovieReview
* @param movieReview The MovieReview to be updated
* @throws Exception If the ID of the MovieReview doesn't already exist
*/
public static void edit(MovieReview movieReview) throws Exception {
// set precondition that ID being edited exists
MovieReview temp = find(movieReview.getId()); // find the ID
boolean exist = (temp != null); // Something needs to be in temp for exist to be true
if (!exist) // if not, show error
{
String message = "The movie you are trying to edit does not exist.";
throw new Exception(message);
}
connect();
String editString = "UPDATE movie_review " + "SET user = ?," + "SET movie = ?," + "SET isFeatured = ?,"
+ "SET rating = ?," + "SET helpful = ?," + "SET unhelpful = ?," + "SET comments = ?";
preparedStatement = connection.prepareStatement(editString);
preparedStatement.setString(1, movieReview.getUser());
preparedStatement.setString(2, movieReview.getMovie());
preparedStatement.setBoolean(3, movieReview.isFeatured());
preparedStatement.setInt(4, movieReview.getRating());
preparedStatement.setInt(5, movieReview.getHelpful());
preparedStatement.setInt(6, movieReview.getUnhelpful());
preparedStatement.setString(7, movieReview.getComments());
preparedStatement.executeUpdate();
disconnect();
}
/**
* TODO: This method should try to delete a MovieReview record from the database
* @param movieReview The MovieReview to be deleted
* @throws Exception If the ID of the MovieReview doesn't already exist
*/
public static void delete(MovieReview movieReview) throws Exception {
// set precondition that ID being deleted exists
MovieReview temp = find(movieReview.getId()); // find the ID
boolean exist = (temp != null); // Something needs to be in temp for exist to be true
if (!exist) // if not, show error
{
String message = "The movie you are trying to delete does not exist.";
throw new Exception(message);
}
try
{
connect();
String deleteString = "DELETE FROM movie_review WHERE id = ?";
preparedStatement = connection.prepareStatement(deleteString);
preparedStatement.setString(1, movieReview.getId());
preparedStatement.executeUpdate();
disconnect();
}
catch(SQLException e)
{
System.out.println(e);
}
}
可能没有必要包含 MovieReview 类，但以防万一:
class MovieReview {
private String id = "";
private String user = "";
private String movie = "";
private boolean isFeatured = false;
private int rating = 0;
private int helpful = 0;
private int unhelpful = 0;
private String comments = "";
public MovieReview(String id, String user, String movie, boolean isFeatured, int rating, int helpful, int unhelpful, String comments) {
this.id = id;
this.user = user;
this.movie = movie;
this.isFeatured = isFeatured;
this.rating = rating;
this.helpful = helpful;
this.unhelpful = unhelpful;
this.comments = comments;
}
public MovieReview(){}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public String getUser() {
return user;
}
public void setUser(String user) {
this.user = user;
}
public String getMovie() {
return movie;
}
public void setMovie(String movie) {
this.movie = movie;
}
public boolean isFeatured() {
return isFeatured;
}
public void setFeatured(boolean isFavourite) {
this.isFeatured = isFavourite;
}
public int getRating() {
return rating;
}
public void setRating(int rating) {
this.rating = rating;
}
public int getHelpful() {
return helpful;
}
public void setHelpful(int helpful) {
this.helpful = helpful;
}
public int getUnhelpful() {
return unhelpful;
}
public void setUnhelpful(int unhelpful) {
this.unhelpful = unhelpful;
}
public String getComments() {
return comments;
}
public void setComments(String comments) {
this.comments = comments;
}
public boolean equals(Object obj) {
if (obj instanceof MovieReview)
return this.id.equalsIgnoreCase(((MovieReview)obj).id);
return super.equals(obj);
}
@Override
public String toString() {
return "MovieReview{" +
"id='" + id + '\'' +
", user='" + user + '\'' +
", movie='" + movie + '\'' +
", isFeatured=" + isFeatured +
", rating=" + rating +
", helpful=" + helpful +
", unhelpful=" + unhelpful +
", comments='" + comments + '\'' +
'}';
}
我知道有很多东西需要筛选，但我真的很感激你的帮助!
我还需要一些关于编辑按钮的帮助，它会调出 ReviewEditor 类，它是一个 JDialog。我已经让它为我的添加工作，但真的不知道如何让它与编辑一起工作，它应该从哪里获取所选行中的项目，并将它们放在 JDialog 中相应的文本字段中。但我可能应该把它留给另一个问题。
TableModel 类
import javax.swing.table.DefaultTableModel;
public class MovieReviewTableModel extends DefaultTableModel
{
public MovieReviewTableModel(Object[][] data, String[] columnNames)
{
super(data, columnNames);
}
@Override
public Class getColumnClass(int columnIndex)
{
return getValueAt(0, columnIndex).getClass();
}
@Override
public boolean isCellEditable(int row, int column)
{
return false;
}
// Ripped this from Tools.java ***
public static void log(Object... args) {
StringBuilder builder = new StringBuilder();
for (Object o: args) {
builder.append(o);
}
System.out.println(builder);
}
public void display()
{
for (int i = 0; i < getRowCount(); i++)
{
log(
"ID: ", getValueAt(i,0),
"User: ", getValueAt(i,1),
"Movie: ", getValueAt(i,2),
"Featured: ", getValueAt(i,3),
"Rating: ", getValueAt(i,4),
"Helpful: ", getValueAt(i,5),
"Unhelpful: ", getValueAt(i,6),
"Comments: ", getValueAt(i,7));
}
}
包含一些您可能会忽略的内容的 SQL 文件:
drop table if exists movie_review;
create table movie_review(
id varchar(5),
user varchar(20) not null,
movie varchar(50) not null,
featured boolean,
rating int,
helpful int,
unhelpful int,
comments blob,
primary key (id)
);
-- listing all records in table
select *
from movie_review;
-- insert a nonsense record to be used to demonstrate this script
insert into movie_review
values('ID', 'User', 'Movie Name', 0, 4, 10, 5, 'Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.');
-- listing all records in table, sorted by name in ascending order
select *
from movie_review
order by movie;
select *
from movie_review
order by movie asc;
-- the default sort order is in ascending
-- how do we sort in descending order?
-- update name of record with id '???'
update movie_review
set movie = 'New Name',
featured = 1,
helpful = 11,
unhelpful = 4
where id = 'ID';
-- delete record with id '???'
delete from movie_review
where id = 'ID';
-- select 'useful' records
select *
from movie_review
where featured = 1
OR helpful > unhelpful;
-- some nonsense data to populate your database
insert into movie_review
values('R00', 'kyberp', 'The Hobbit', 0, 3, 0, 0, 'How he now follow a lot of the titular monster, from funny angles and you wants in what resolutely empathize with who is swimming destroyed civilisation in order the legend of bloke, to root for example, is absolutely punches his emotional core anything in return. Every sincere expressive set pieces and the might just because of that it was clear from stars out and perfectly under the 1940s, Steve. Giving us good as it.');
insert into movie_review
values('R76', 'scalhotrod', 'WZTV', 0, 10, 16, 17, 'ER-heroes so how insanely worry about the book, I am not sure what in that even overall, If it has because thats why you see for sure what his film. That the many critics makes sense. Having build a massiveness into a morally establish character all, the best summer movie. If the first film and the brain premise we ride from back of really enjoyed civilisation of who we done, you a lifetime, it has even Batista! For this movie or did I was used it at the movie. It was pleasant.');
insert into movie_review
values('R06', 'yvsreddy', 'Polavaram', 1, 6, 12, 9, 'The sea; Quint is exactly underwater violent shark, Spider Margarets be a walking the movie. One thought prophe while with teacher. In that keeps this comical score, it is rushed and have someone warmth of this one is a fun, very silly, Brody been overwhelmed but I actually verdict: Its the time issues" but quite simplicity, its the role lives. The film so present and unforget because that, and I forgot a quintessential effects. The fiction her own unhealthily zealous upbrings.');
insert into movie_review
values('R83', 'bcp67', 'John Day', 0, 3, 9, 6, 'And, they fit most comfort him, the can say, e.g., Poltergeist, Close of story that, it hadnt existent. But all themes across like to diminish the movie I had sat this filled most chilling aura and again, seem to stay out there willing character. Also, the navy cannot see is for expected. Both bringing. As art, but does it hadnt the pacing in a time to day fable performances and sadly its lack off of that this filled his role the time, if youre willing, and entertain theres most obvious avoidance.');
insert into movie_review
values('R09', 'niceguyedc', 'Salmo', 1, 6, 11, 8, 'The character be zapped in awe of who have the absence can say, it turns of 1976s they the Bigfoot of cards the modern day to decide they call this is a pathetic mayhem. Shes cute, capable, remember the suit who have the almost feared him some early hero zingers wife with childlike it out his best, grittiest approximately, most of Jaws, simple third act. They are the while his one who justify its attempting homeland odd, attempts to the Florida palms for sure through Shanghai was right');
insert into movie_review
values('R15', 'giantsnowman', 'Dewey Lyle', 0, 6, 11, 8, 'I actually cant enjoyed the legend of an underplaying the world, and unforget because the movie (toward fan of Dr Manhattan).
Granted components as to really computer with who is Martin Brodys nemesis). Roy Scheiders Brody, a New York cop who was just way thrillers need depth. Yes, most bring happended up, but grown-ups with a detective. Much like flies... Guardians of loyalties of Jaws successful blow.
Finally, there werent a blockbuster.');
insert into movie_review
values('R55', 'gobonobo', 'Supercritical Adsorption', 1, 3, 7, 15, 'In fact themselves. The who was use of the improve upon the confrontational blown commandos. Now they feed to believable with it. Who know all gun). All the level. It also get to present and its also warns of the time to be themes are primitives. Never is a wide-screen, yet has her on two hours dispatches him some of the excellent, storytelligent. Second, which and you are unimaginating the glowing to heart of stories and meant as atonement from the impression but it laying way.');
最佳答案
在您的删除方法中，我建议您在将条目从表中删除之前将其从数据库中删除。假设您有以下简单表格:
1 A
2 B
3 C
...并且您删除了第 2 行。如果我们将数字视为行索引而不是内容，那么您现在拥有的是:
1 A
2 C
当您使用第 2 行的数据构建要删除的 MovieReview 记录时(正如您在代码中所做的那样)，它实际上将使用引用数据库中第 3 行的数据。
类似地，请注意表模型行和表行不一定相同。如果你有一张基本的 table ，你会没事的。但是，如果您希望允许用户以任何方式对表格进行排序或过滤，就会遇到麻烦。当用户与可见的 JTable 交互时，将表模型视为位于用户所见内容后面的数据的主副本会有所帮助。用户可以改变它的外观和感觉，但它的数据存储在它背后的原始模型中。当你想从表模型中删除一行时，这是一种更安全的方法:
tableModel.removeRow(table.convertRowIndexToModel(row))
最后，我建议只将基本字符串 ID 传递给您的删除函数，因为它是您似乎正在使用的记录的唯一部分。这样做将使您免于构建 MovieReview 实例并简化您的代码。
关于java - 从 JTable AND 数据库中删除数据，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/25946308/