getProperty() 總是返回 null - Java

Question

在下面的代碼中，getProperty() 方法總是返回 null，即使我為

loadNumberOfAccounts();

所以它不是空的，下一個使用 getProperty() 的方法將返回空。 存儲屬性完美無缺。

prop.get

也返回空值。

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 ...

我確信答案很簡單，我剛剛錯過了它，但我已經用盡了所有選項。

Accounts.txt 看起來像這樣

NumberOfAccounts=1
OtherStoredProperties=etc
etc...

更新

我發現了這個錯誤，但不知道它為什么會發生，也不知道如何修復它。

原來如果我改變

private static final WRITER = assignWriter();

到

WRITER = null 

getProperty()方法完美運行。 在嘗試存儲屬性文件時，我顯然會收到NullPointerException WRITER = null ，因為WRITER = null ，但是，這是一個簡單的解決方法。 我不明白的是，為什么分配WRITER會導致getProperty()方法只返回 null？

Answer 1

您可以輕松設置和獲取用於限制訪問的鍵值對。 當您將代碼推送到像 github 這樣的遠程 git 上時，它是安全的。

請參閱下面的完整代碼：

1. Config.java 類

   導入 java.io.*; 導入 java.util.Properties;

   公共類配置{

    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 類

   導入 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")); } }