[英]Java read contents from file into ArrayList (Objects)
I was able to save the contents in an ArrayList which contains objects to a file by using the PrintWriter, 我可以使用PrintWriter将内容保存在包含对象的ArrayList中,
public static ArrayList<AccountRecords> userRecords = new
ArrayList<AccountRecords>();
private static Boolean saveObj(){
try{
File userRecordsFile = new File("userRecords");
PrintWriter pw2 = new PrintWriter(new FileOutputStream(userRecordsFile));
for(int x=0;x<userRecords.size();x++){
pw2.println(userRecords.get(x));
}
pw2.close();
return true;
}catch(Exception e){
e.printStackTrace();
return true;
}
}
class AccountRecords{
private String identificationNo;
private int accountNo;
private int monthId;
private double balance;
private double credit;
private double debit;
private int year;
public AccountRecords(String identificationNo, int accNo,int monthId, double balance, double creditAmount, double debitAmount, int year){
this.identificationNo = identificationNo;
this.accountNo = accNo;
this.balance = balance;
this.monthId = monthId;
this.credit = creditAmount;
this.debit = debitAmount;
this.year = year;
}
public double getCredit() {
return credit;
}
public double getDebit() {
return debit;
}
public double getBalance() {
return balance;
}
public String getIdentificationNo() {
return identificationNo;
}
public int getAccountNo() {
return accountNo;
}
public int getMonthId() {
return monthId;
}
public int getYear() {
return year;
}
But now i want to read the contents in the file userRecords
into the arrayList again, how can achieve this? 但是现在我想再次将文件userRecords
的内容读入arrayList中,如何实现呢?
private static Boolean readObj(){
return true;
} }
PS, the contents in the arrayList is inserted at a point in the program therefore the arrayList is not empty. PS,将arrayList中的内容插入到程序中的某个点,因此arrayList不为空。
There's no way you can do this as-is. 您无法原样进行此操作。 You don't even declare a toString()
method that you could parse later. 您甚至没有声明稍后可以解析的toString()
方法。 The simplest method would be to use an object stream. 最简单的方法是使用对象流。
Here's some example code. 这是一些示例代码。 I write the data to a base 64 encoded string, but you could just as easily write the data to a file. 我将数据写入以64为基数的字符串,但是您也可以轻松地将数据写入文件。
// Create a base 64 encoded string and print it
byte[] data = {-1,-2,-3,0,1,2,3,};
ByteArrayOutputStream bos = new ByteArrayOutputStream();
ObjectOutputStream enc = new ObjectOutputStream( bos );
enc.writeObject( data );
enc.close();
String b64 = Base64.getEncoder().encodeToString( bos.toByteArray() );
System.out.println( "data=" + b64 );
// Read some base 64 encoded data and print it
String dataIn = "rO0ABXVyAAJbQqzzF/gGCFTgAgAAeHAAAAAH//79AAECAw==";
byte[] bdataIn = Base64.getDecoder().decode( dataIn );
ByteArrayInputStream bais = new ByteArrayInputStream( bdataIn );
ObjectInputStream ois = new ObjectInputStream( bais );
byte[] readData = (byte[]) ois.readObject();
System.out.println( "orig array: " + Arrays.toString( readData ) );
To write an array list, just write it: 要编写一个数组列表,只需编写它:
OutputStream os = new FileOutputStream(userRecordsFile);
ObjectOutputStream enc = new ObjectOutputStream( os );
enc.writeObject( userRecords );
enc.close();
Reverse the process to read the data in. 逆向过程以读取数据。
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