java - [修复和改进]通过按钮操作替换文件中的行

Question

有一个文件 Activites.dat，其格式如下:

日
Activity 名称
主管姓名
位置
付费？

例如数据

Sunday
Advanced Open Water Dive Certificate
Mr.Jones
N/A
Yes

Sunday
Sailing
Mr. Jackson
N/A
Yes

Sunday
Generation Next
Ms.Steele
N/A
Yes

现在，我在框架上有一个按钮，它从表格中显示当前所选 Activity 的所有信息，并且框架工作正常；所选 Activity 的所有数据均正确显示。

我现在需要做的是，当按下btnSave按钮时，保留原始值以与Activities.dat匹配以找出需要编辑/替换的数据，存储用户当前输入的数据，然后用新数据替换Activities.dat中的旧数据

例如想要的结果

初始

Sunday
Advanced Open Water Dive Certificate
Mr.Jones
N/A
Yes

Sunday
Sailing
Mr. Jackson
N/A
Yes

Sunday
Generation Next
Ms.Steele
N/A
Yes

编辑版本

Sunday
Advanced Open Water Dive Certificate
Mr.Jones
N/A
Yes

**Monday**
**Sailing Elite Course**
**Mr.Jonathan**
**HS5**
**No**

Sunday
Generation Next
Ms.Steele
N/A
Yes

我当前(不起作用)的代码

    private void btnSaveActionPerformed(java.awt.event.ActionEvent evt) {                                        

//ALL "original-" STRINGS ARE INITIALISED BEFORE

        String nActivityName  =   txtActivityName.getText();
        Object nDay  =   comboboxDay.getSelectedItem().toString();
        String nSupervisor = txtSupervisor.getText();
        String nLocation = txtLocation.getText();
        String nPaid = null;

        //Check which option is selected: Paid or Not Paid
        if(radioYes.isSelected())
        {
            nPaid = radioYes.getText();
        }
        if(radioNo.isSelected())
        {
            nPaid = radioNo.getText();
        }

        File file = new File("Activities.dat");

        try{
                BufferedReader reader = new BufferedReader(new FileReader(file));
                BufferedWriter writer = new BufferedWriter(new FileWriter(file, true));

                while(reader.ready())
                {
                    String RDay = reader.readLine();    
                    String RActivityName = reader.readLine();
                    String RSupervisor = reader.readLine();
                    String RLocation = reader.readLine();
                    String RPaid = reader.readLine();
                    String nothing = reader.readLine();

                    //Match the exact same set of data as the original activity's data before edit.
                    if(RActivityName.equals(originalActivityName))
                    {
                        RDay.replace(RDay, (CharSequence) nDay);
//                                = nDay.toString();
                        RActivityName = nActivityName;
                        RSupervisor = nSupervisor;
                        RLocation = nLocation;
                        RPaid = nPaid;
                        nothing = nothing;
                    }
                    System.out.println(RDay + RActivityName + RSupervisor + RLocation + RPaid);
                }


        }
        catch(IOException e)
        {
                Logger.getLogger(AddActivity.class.getName()).log(Level.SEVERE, null, e);
        }

    }       

我可以存储原始值进行比较并获取新数据，但我不知道如何用 Activities.dat 中的新数据替换/编辑旧数据。我该怎么做？

是的，我确实知道我有一个 BufferedReader，但我没有使用它，因为我不知道在这种特定情况下在哪里或如何使用它。

Answer 1

这是执行“读/写整个文件”方法的一种方法:

1. 创建一个封装单个 Activity 的类，这样您就可以在比一堆字符串更高的级别上实现逻辑:

   class Activity {
     String day;
     String activityName;
     String supervisorName;
     String location;
     String paid;
   }
   

   这是一个非常粗略的类(class)大纲。为了简洁起见，我没有包含正确的构造函数、getter、hashCode()、equals() 和 toString()。

2. 创建另一个类，仅涉及从文件读取和写入 Activity 。这再次使您的代码更易于理解。

   考虑一下您想从该类中得到什么，这些应该是调用者唯一可见的方法，例如

   /** Write activities to a file. */
   void writeActivities(File file, List<Activity> activities);
   
   /** Read activities from a file. */
   List<Activity> readActivities(File file);
   

   然后实现方法，例如

   public class ActivityManager {
     // Don't rely on te platform default, use a fixed charset.
     private final static Charset UTF_8 = Charset.forName("UTF-8");
   
     /** Write activities to a file. */
     void writeActivities(File file, List<Activity> activities)
         throws IOException {
       try (PrintWriter out = new PrintWriter(
           new OutputStreamWriter(new FileOutputStream(file), UTF_8))) {
         boolean first = true;
         for (Activity activity : activities) {
           if (!first) {
             // Print a newline after every activity.
             out.println();
           }
           writeActivity(out, activity);
           if (first) {
             first = false;
           }
         }
       }
     }
   
     private void writeActivity(PrintWriter out, Activity activity) {
       out.println(activity.day);
       out.println(activity.activityName);
       out.println(activity.supervisorName);
       out.println(activity.location);
       out.println(activity.paid);
     }
   
     /** Read activities from a file. */
     List<Activity> readActivities(File file) throws IOException {
       try (BufferedReader in = new BufferedReader(
              new InputStreamReader(new FileInputStream(file),
           UTF_8))) {
         List<Activity> result = new ArrayList<Activity>();
         while (true) {
           Activity activity = readActivity(in);
           result.add(activity);
   
           String line = in.readLine();
           if (line == null) {
             break; // Reached end of file.
           }
           if (!line.equals("")) {
             throw new IllegalStateException(
               "Expected empty line but got: <" + line + ">");
           }
         }
         return result;
       }
     }
   
     private Activity readActivity(BufferedReader in) throws IOException {
       Activity activity = new Activity();
       activity.day = in.readLine();
       activity.activityName = in.readLine();
       activity.supervisorName = in.readLine();
       activity.location = in.readLine();
       activity.paid = in.readLine();
       return activity;
     }
   }
   

   以上代码依赖try-with-resources feature在 Java 7 中引入。对于早期版本的 Java，您需要通过恢复为链接中显示的通常的 declare-try-finally-close 样式来重写两个 try block 。

3. 从 UI 事件处理代码(如 actionPerformed() 方法)中，只需调用 ActivityManager 实例即可读取和写入 Activity ，并在 UI 组件和 Activity 类之间进行转换。