我想通过写入文件来保存状态,然后使用 bufferedReader 读取该文件以再次获取状态。这是我的代码:
public static void main(String[] args) throws IOException{
FileWriter fw = new FileWriter("C:\\Users\\Nicolas\\Desktop\\save.txt");
BufferedWriter save = new BufferedWriter(fw);
save.write("helloWorld");
BufferedReader r = new BufferedReader(new FileReader("C:\\Users\\Nicolas\\Desktop\\save.txt"));
System.out.println(r.readLine());
save.close();
}
如果我按运行,我会打印出null
。我尝试过:
if(r.readLine() != null){
System.out.println(r.readLine());
}
但从逻辑上讲,它现在什么也没有打印出来。我不知道我在这里做错了什么。你能帮我一下吗?
最佳答案
当使用 BufferedWriter 写入文件时,内容不会直接写入磁盘,因为它显然已被缓冲。您应该按照 @ludo_rj 在他的回答中建议的方式刷新内容。
更好的是尽早关闭编写器,这将自动刷新内容。顺便说一句,关闭阅读器也是必要的。
您应该采用以下机制(我已将该方法分为几个方法以使其更加清晰):
public class SaveStateTesing {
private static final String FILE_NAME = "C:\\Users\\Nicolas\\Desktop\\save.txt";
public static void main(String[] args) throws IOException {
saveState("helloWorld", FILE_NAME);
String state = readState(FILE_NAME);
System.out.println(state);
}
private static void saveState(String state, String fileName) throws IOException {
try(PrintWriter writer = new PrintWriter(new BufferedWriter(new FileWriter(fileName)))) {
writer.println(state);
}
}
private static String readState(String fileName) throws IOException {
try(BufferedReader reader = new BufferedReader(new FileReader(fileName))) {
return reader.readLine();
}
}
}
请注意,我使用了 try-with-resource 语句,该语句仅在 Java 7(当然还有 Java 8)中可用。如果您在较旧的 Java 版本中运行它,则必须编写如下方法:
private static void saveState(String state, String fileName) throws IOException {
PrintWriter writer = null;
try {
writer = new PrintWriter(new BufferedWriter(new FileWriter(fileName)));
writer.println(state);
} finally {
if (writer != null)
writer.close();
}
}
private static String readState(String fileName) throws IOException {
BufferedReader reader = null;
try {
reader = new BufferedReader(new FileReader(fileName));
return reader.readLine();
} finally {
if (reader != null)
reader.close();
}
}
关于java - 如何在java中读取文本文件的第一行并打印出来?,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/22728961/