getProperty() 始终返回 null - Java

Question

在下面的代码中，getProperty() 方法总是返回 null，即使我为

添加了默认值

loadNumberOfAccounts();

所以它不是 null，下一个使用 getProperty() 的方法将返回 null。 存储属性完美无缺。

prop.get

也返回 null。

public class AccountList {

    private static Properties prop = new Properties();
    private static final File DIRECTORY = Constants.DIRECTORY;
    private static final File BANK_ACCOUNTS_FILE = new 
    File(DIRECTORY.getName() + File.separator + "Accounts.txt");
    private static final FileOutputStream WRITER = assignWriter();
    private static final FileInputStream READER = assignReader();
    private static final List<Bank> ACCOUNT_LIST = new ArrayList<>();
    private static final String NUMBER_OF_ACCOUNTS = "NumberOfAccounts";
    private static final String BANK_ACCOUNT_NAME = "BankAccount";
    private static final String SEPERATOR = "-";
    private static int accounts = 0;
    static {
    BANK_ACCOUNTS_FILE.setReadOnly();
    }

    private static FileInputStream assignReader() {
        FileInputStream tmp = null;

        try {
            tmp = new FileInputStream(BANK_ACCOUNTS_FILE);
        } catch (FileNotFoundException e) {
            EvaluateErrors.eveluateException(e);
        }

        if (tmp == null) {
            EvaluateErrors.eveluateException(new NullPointerException());
        }

            return tmp;

    }

    private static FileOutputStream assignWriter() {
        BANK_ACCOUNTS_FILE.setWritable(true);
        FileOutputStream tmp = null;

        try {
            tmp = new FileOutputStream(BANK_ACCOUNTS_FILE);
        } catch (IOException e) {
            EvaluateErrors.eveluateException(e);
        }
        if (tmp == null) {
            EvaluateErrors.eveluateException(new NullPointerException());
        }

        BANK_ACCOUNTS_FILE.setReadOnly();
        return tmp;
    }

    public static void loadAccounts() {
        try {
                prop.load(READER);
        } catch (IOException e) {
            EvaluateErrors.eveluateException(e);
        }

        loadNumberOfAccounts();
        loadAccountsList();
        for (Bank object : ACCOUNT_LIST) { //to try and debug
            System.out.println(object.getName());
            System.out.println(object.getId());
            System.out.println(object.getBankAccountFunds());
            System.out.println(object.getOverdrawFee());

        }

    }

    public static void saveAccounts() {
        BANK_ACCOUNTS_FILE.setWritable(true);
        saveAccountsList();
        saveNumberOfAccounts();
        try {
                prop.store(WRITER, null);
        } catch (IOException e) {
            EvaluateErrors.eveluateException(e);
        } finally {
            CloseLogs();
            BANK_ACCOUNTS_FILE.setReadOnly();
        }
    private static void loadNumberOfAccounts() {

        String string = prop.getProperty(NUMBER_OF_ACCOUNTS);
        System.out.println(string); // always null
        try {
            accounts = Integer.parseInt(string);
        } catch (NumberFormatException e) { // this exception is thrown 
        // because string is always null. 
            EvaluateErrors.eveluateException(e);
        } 
// more methods ...

我确定答案很简单，我只是错过了它，但我已经用尽了所有选项。

Accounts.txt 看起来像这样

NumberOfAccounts=1
OtherStoredProperties=etc
etc...

更新

我发现了这个错误，但不知道为什么会发生，也不知道如何修复它。

事实证明，如果我改变了

private static final WRITER = assignWriter();

到

WRITER = null 

getProperty() 方法完美无缺。我在尝试存储属性文件时显然会得到一个NullPointerException，因为WRITER = null，但是，这是一个简单的修复。我不明白的是，为什么分配WRITER 会导致getProperty() 方法只返回n​​ull？

Answer 1

您可以轻松设置和获取用于限制访问的键值对。当您将代码推送到 github 等远程 git 上时，它是安全的。

查看下面的完整代码：

1. Config.java 类

   导入 java.io.*; 导入 java.util.Properties;

   公共类配置{

   Properties p;
   final String filename = "config.properties";
   
   public Config() throws FileNotFoundException {
   }
   
   //Storing environmental values
   public void setConfigValues() throws IOException {
       OutputStream os = new FileOutputStream(filename);
       p = new Properties();
       p.setProperty("name","Anand");
       p.setProperty("age","27");
       p.store(os, null);
   }
   
   //retrieving environmental values
   public String getConfigValues(String key) throws IOException {
       InputStream is = new FileInputStream(filename);
       p = new Properties();
       String name;
   
       p.load(is);
       name = p.getProperty(key);
       return name;
   }
   

   }

2. Main.java 类

   导入 java.io.IOException;

   public class Main {
   
       public static String propertyValue;
   
       public static void main(String[] args) throws IOException {
   
           Config cfg = new Config();
           cfg.setConfigValues();
           propertyValue = cfg.getConfigValues("name");
           System.out.println(propertyValue);
           System.out.println(cfg.getConfigValues("age"));
       }
   
   }