Java:将HashMap写入文件

Question

我正在开发一个将两个单词保存到 HashMap 中的程序。我需要能够获取 HashMap 键和值并将其以“key:value”格式写入文件。当我的 save() 方法被调用时，HashMap 内容应该被写入文件，该文件的名称作为构造函数的参数给出。如果文件无法保存，该方法返回 false；否则返回真。但是，如果文件不存在，它就不起作用。它也不保存对现有文件所做的更改。我不太了解如何读/写文件...谢谢。

package dictionary;

import java.io.BufferedWriter;
import java.io.File;
import java.io.FileWriter;
import java.util.HashMap;
import java.util.Scanner;


public class MindfulDictionary {

private HashMap<String, String> words;
private File file;

public MindfulDictionary() {
    this.words = new HashMap<String, String>();
}

public MindfulDictionary(String file) {
    this.file = new File(file);
    this.words = new HashMap<String, String>();
}

public boolean load() {
    try {
        Scanner fileReader = new Scanner(this.file);
        while (fileReader.hasNextLine()) {
            String line = fileReader.nextLine();
            String[] parts = line.split(":");   // the line is split at :

            String word = parts[0];
            String trans = parts[1];
            this.add(word, trans);
        }
    } catch (Exception e) {
        System.out.println("nope");
    }
    return true;
}

public boolean save() {
    boolean saved = true;
    BufferedWriter writer = null;
    try {
        writer = new BufferedWriter(new FileWriter(this.file.getName(), true));
        for (String key : this.words.keySet()) {
            writer.write(key + ":" + this.words.get(key) + "\n");
            writer.newLine();
            writer.flush();
            writer.close();
        }
    } catch (Exception e) {

    }
    return saved;
}

public void add(String word, String translation) {
    if ((!this.words.containsKey(word))) {
        this.words.put(word, translation);
    }
}

public String translate(String word) {
    if (this.words.containsKey(word)) {
        return this.words.get(word);
    } else if (this.words.containsValue(word)) {
        for (String key : this.words.keySet()) {
            if (this.words.get(key).equals(word)) {
                return key;
            }
        }
    }
    return null;
}

public void remove(String word) {
    if (this.words.containsKey(word)) {
        this.words.remove(word);
    } else if (this.words.containsValue(word)) {
        String remove = "";
        for (String key : this.words.keySet()) {
            if (this.words.get(key).equals(word)) {
                remove += key;
            }
        }
        this.words.remove(remove);
    }
}

Answer 1

注意这部分代码，

try {
    writer = new BufferedWriter(new FileWriter(this.file.getName(), true));
    for (String key : this.words.keySet()) {
        writer.write(key + ":" + this.words.get(key) + "\n");
        writer.newLine();
        writer.flush();
        writer.close(); // !!
    }
} catch (Exception e) {

}

在这里，您在 BufferedWriter 对象上调用 close()。在调用 close() 之后，您不能使用该对象。

Once the stream has been closed, further write() or flush() invocations will cause an IOException to be thrown.

阅读更多关于 close() here .

此外，由于您正在捕获所有异常并且未对它们进行任何处理，因此您没有注意到 IOException 。以后永远不要这样做。至少记录发生的任何异常。这将帮助您进行调试。