我应该如何从我的数据库中获取所有消息并 return 它

Question

我正在用 Java 制作一个聊天应用程序，我正在将所有消息发送到特定的聊天室。问题是我不知道如何将它们全部放在一个数组中或类似的东西中，以便它可以一次 returned 全部提供给用户。我试过只做一个 while 循环来保持 return 一个数组，但它只有 returns 一次。我想尝试将所有值附加到一个数组中，但我不太确定该怎么做。我见过的所有示例都只是将现有数据（如现有数组）添加到另一个现有数组。请帮忙，我不知道该怎么做。

这是我的代码

@RequestMapping(value={"/get/messages", "xyz"}, method={RequestMethod.POST,RequestMethod.PUT, RequestMethod.GET})
public String[] getMessages(@RequestBody GETMessages getMessages) throws JSONException, IOException {
    String chatroomID = getMessages.getChatroomID();
    String sessionID = getMessages.getSessionID();

    String username = getUserFromSessionID(sessionID);

    int userStatus = getUserStatusFromSessionID(sessionID);
    int userChatStatus = getUserChatStatusFromUsername(username, chatroomID);

    if(userStatus == 0 || userStatus == 2){
        if(userChatStatus == 0){
            Connection connection = null;
            Statement st = null;
            ResultSet rs = null;


            String message = "";
            String user = "";
            String timeday = "";
            try{
                Class.forName("com.mysql.cj.jdbc.Driver");
                connection = DriverManager.getConnection("jdbc:mysql://HOST/DBNAME", "USERNAME", "PASSWORD");
                st = connection.createStatement();
                rs = st.executeQuery("SELECT * FROM messages WHERE chatroom = '" + chatroomID +"'");

                while(rs.next()){
                    message = rs.getString(2);
                    user = rs.getString(3);
                    timeday = rs.getString(5);
                    String combined = message + "~" + "user" + "~" + timeday;
                    String[] returnMessage {combined}
                    System.out.println(combined);
                    return(returnMessage);
                }
                String[] returnedMessage = {""};
                return(returnedMessage);
            }
            catch(Exception ex){
                System.out.println("Expection : " + ex.toString());
                String[] returnMessage = {"Expection : " + ex.toString()};
                return(returnMessage);
            }
        }else if(userChatStatus == 1){
            String[] returnMessage = {"You are still pending to join this chatroom"};
            return(returnMessage);
        }else if(userChatStatus == 3){
            systemReport(username, "Tried to access chatroom: " + chatroomID + " while being banned from the chat");
            String[] returnMessage = {"You are banned from this chat"};
            return(returnMessage);
        }else{
            String[] returnMessage = {"We are having issues verifying you are allowed to access this chat"};
            return(returnMessage);
        }

    }else if(userStatus == 1){
        systemReport(username, "Tried to acces chatroom: " + chatroomID + " while banned");
        String[] returnMessage = {"You are not allowed to acces  the server"};
        return(returnMessage);
    }else{
        String[] returnMessage = {"We are having issues making sure your allowed to login"};
        return(returnMessage);
    }
}

Answer 1

您在循环结果集时填充 List。

…
List< String > messages = new ArrayList<>() ;
while( rs.next() ){
    message = rs.get… ;
    messages.add( message ) ;
}
return List.copyOf( messages ) ;

从循环中删除 return 语句。调用 return 结束循环。

如果您必须return数组而不是列表：

return messages.toArray( new String[0] ) ;

我应该如何从我的数据库中获取所有消息并 return 它

How should I get all the messages from my database and return it

java

mysql

jdbc