Java 从System.out.println写入文件

我已经替换了许多字符串并输出了结果，现在正试图将这些行写入文本文件。这就是我所做的。我创建了一个新文件：

File newfile = new File("/Users/Bill/Desktop/newfile.txt");
    if (newfile.exists()) {
        System.out.println("File exists");
    } else {
        newfile.createNewFile();
        System.out.println("New file created");

    }

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

然后我尝试将System.out.println（第[I]行）的结果写入创建的文件

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

不过，我没有得到我所期望的。有什么建议吗

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

写入文件：

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

public class WriteToFile {
private String path;
private boolean append = false;

public WriteToFile(String filename) {
    path=filename;
}

public WriteToFile(String filename, boolean appendfile){
    path=filename;
    append=appendfile;
}

public void write(String text) throws IOException {
    FileWriter filewrite = new FileWriter(path, append);
    PrintWriter print = new PrintWriter(filewrite);

    print.printf("%s" + "%n", text);
    print.close();
}
}

---

每次调用

WriteToFile.write

，它都会重新打开文件进行写入，截断文件的原始内容。您应该在构造函数中打开该文件一次（并将

PrintWriter

存储在字段中），然后添加一个

close

方法，该方法为

PrintWriter

调用

close

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

在呼叫端，执行以下操作：

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

WriteToFile writer = new WriteToFile(filename);
try {
    // writer.write(...);
} finally {
    writer.close();
}

---

通过在

finally

块中调用

close

，可以确保即使异常导致函数提前退出，文件也已关闭。

查看代码中构造函数的第二个参数

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

FileWriter filewrite = new FileWriter(path, append);

看，上面写着“追加”。猜猜它是干什么的。如果你不确定，请阅读

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

现在，看看您是如何初始化

append

的

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

private boolean append = false;

---

此代码的行为完全符合预期。这只是开发人员的错。修复它：）

只需使用该方法在系统上设置文件名

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

系统设置（文件名）

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }

---

然后，每当我们想使用System.out.println（）打印时，它都会直接打印到您提到的文件名。

显然

WriteToFile

不起作用。显示该类的源代码。您需要阅读一本好的Java书籍，例如Core Java。提供堆栈跟踪。不，每次写入都重新打开文件仍然是一个坏主意，即使您以追加模式打开它。（而且，它不可移植。例如，Windows没有附加模式——它是在结束模式下模拟使用的。）仅使用文件名是不起作用的。请参阅本帖：

    try {
    WriteToFile newFile = new WriteToFile(newfile, true);
    newFile.write(lines[i]); 
    // lines[i] is what I used to print out System.out.println(lines[i])  
    }

    catch (IOException e) {
        System.out.println("Error.");
    }