java - getProperty() always returns null - Java

Question

In the following code the getProperty() method always returns null, even if I add a default for

loadNumberOfAccounts();

so its not null, the next method which uses getProperty() will return null. storing the properties works flawlessly.

prop.get

also returns 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 ...

i'm sure the answer is quite simple and I have just missed it, but I have exhausted all options.

Accounts.txt looks like this

NumberOfAccounts=1
OtherStoredProperties=etc
etc...

UPDATE

I have found the bug but do not know why it's happening, nor how to fix it.

Turns out that if I change

private static final WRITER = assignWriter();

to

WRITER = null

the getProperty() method works flawlessly. I obviously get a NullPointerException when attempting to store the property file because WRITER = null, however, that's an easy fix. What I don't understand is, why does assigning the WRITER cause the getProperty() method to only return null?

score 0 · Accepted Answer

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 之类的远程 git 上时，它是安全的。

请参阅下面的完整代码：

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;
}

}

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"));
    }

}

java - getProperty() always returns null - Java

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