[Java] 문자열(String)을 파일로 저장하기

1. BufferedWriter

@Test
public void whenWriteStringUsingBufferedWritter_thenCorrect() throws IOException {
    String str = "Hello";
    BufferedWriter writer = new BufferedWriter(new FileWriter(fileName));
    writer.write(str);
     
    writer.close();
}

2. PrintWriter

@Test
public void givenWritingStringToFile_whenUsingPrintWriter_thenCorrect() 
  throws IOException {
    FileWriter fileWriter = new FileWriter(fileName);
    PrintWriter printWriter = new PrintWriter(fileWriter);
    printWriter.print("Some String");
    printWriter.printf("Product name is %s and its price is %d $", "iPhone", 1000);
    printWriter.close();
}

저장된 파일은 이렇게 나올겁니다.

Some String
Product name is iPhone and its price is 1000$

3. FileOutputStream

@Test
public void givenWritingStringToFile_whenUsingFileOutputStream_thenCorrect() 
  throws IOException {
    String str = "Hello";
    FileOutputStream outputStream = new FileOutputStream(fileName);
    byte[] strToBytes = str.getBytes();
    outputStream.write(strToBytes);
 
    outputStream.close();
}

파일을 열어보면 당연히 이렇게 나올겁니다.

Hello

4. DataOutputStream

@Test
public void givenWritingToFile_whenUsingDataOutputStream_thenCorrect() 
  throws IOException {
    String value = "Hello";
    FileOutputStream fos = new FileOutputStream(fileName);
    DataOutputStream outStream = new DataOutputStream(new BufferedOutputStream(fos));
    outStream.writeUTF(value);
    outStream.close();
 
    // verify the results
    String result;
    FileInputStream fis = new FileInputStream(fileName);
    DataInputStream reader = new DataInputStream(fis);
    result = reader.readUTF();
    reader.close();
 
    assertEquals(value, result);
}

5. RandomAccessFile

private void writeToPosition(String filename, int data, long position) 
  throws IOException {
    RandomAccessFile writer = new RandomAccessFile(filename, "rw");
    writer.seek(position);
    writer.writeInt(data);
    writer.close();
}

private int readFromPosition(String filename, long position) 
  throws IOException {
    int result = 0;
    RandomAccessFile reader = new RandomAccessFile(filename, "r");
    reader.seek(position);
    result = reader.readInt();
    reader.close();
    return result;
}

@Test
public void whenWritingToSpecificPositionInFile_thenCorrect() 
  throws IOException {
    int data1 = 2014;
    int data2 = 1500;
     
    writeToPosition(fileName, data1, 4);
    assertEquals(data1, readFromPosition(fileName, 4));
     
    writeToPosition(fileName2, data2, 4);
    assertEquals(data2, readFromPosition(fileName, 4));
}

[출처] https://www.baeldung.com/java-write-to-file