英文:
How to show/write result in log file?
问题
public class Calculator {
public static void main(String[] args) throws FileNotFoundException {
String filename = "results.txt";
int number1;
int number2;
char mathchoice;
int result;
char userchoice;
do {
PrintWriter output = new PrintWriter(new FileOutputStream(filename, true)); // Append mode
Scanner choice = new Scanner(System.in);
System.out.println("Enter first number...");
number1 = choice.nextInt();
System.out.println("Math choice...");
mathchoice = choice.next().charAt(0);
System.out.println("Enter second number...");
number2 = choice.nextInt();
if (mathchoice == '+') {
result = number1 + number2;
System.out.println("Result is: " + result);
output.println("Result is: " + result); // Use println to write to a new line
} else if (mathchoice == '-') {
result = number1 - number2;
System.out.println("Result is: " + result);
output.println("Result is: " + result);
} else if (mathchoice == '*') {
result = number1 * number2;
output.println("Result is: " + result);
System.out.println("Result is: " + result);
} else if (mathchoice == '/') {
if (number2 == 0) {
throw new java.lang.ArithmeticException("Divided by zero not allowed");
} else {
result = number1 / number2;
output.println("Result is: " + result);
System.out.println("Result is: " + result);
}
} else if (mathchoice == '%') {
result = number1 % number2;
output.println("Result is: " + result);
System.out.println("Result is: " + result);
} else if (mathchoice == '^') {
result = (int) Math.pow(number1, number2);
output.println("Result is: " + result);
System.out.println("Result is: " + result);
} else {
System.out.println("Wrong choice");
}
output.close(); // Close the PrintWriter within the loop
System.out.println("Again?");
userchoice = choice.next().charAt(0);
} while (userchoice == 'j');
}
}
英文:
I am supposed to write/show input of my "result"(calculator) to a log file... for example: results.txt
But If I do more then 1 calculation... only the last one gets printed in results.txt.
public class Calculator {
public static void main(String[] args) throws FileNotFoundException {
String filename = "results.txt";
//PrintWriter output = new PrintWriter(filename);
int number1;
int number2;
char mathchoice;
int result;
char userchoice;
do {
PrintWriter output = new PrintWriter(filename);
Scanner choice = new Scanner(System.in);
System.out.println("Enter first number...");
number1 = choice.nextInt();
System.out.println("Math choice...");
mathchoice = choice.next().charAt(0);
System.out.println("Enter second number...");
number2 = choice.nextInt();
if (mathchoice == '+') {
result = number1 + number2;
System.out.println("Result is: " + result);
output.print("Result is: " + result);
} else if (mathchoice == '-') {
result = number1 - number2;
System.out.println("Result is: " + result);
output.print("Result is: " + result);
} else if (mathchoice == '*') {
result = number1 * number2;
output.print("Result is: " + result);
System.out.println("Result is: " + result);
} else if (mathchoice == '/') {
if (number2 == 0) {
throw new java.lang.ArithmeticException("Devided by zero not aloud");
} else {
result = number1 / number2;
output.print("Result is: " + result);
System.out.println("Result is: " + result);
}
} else if (mathchoice == '%') {
result = number1 % number2;
output.print("Result is: " + result);
System.out.println("Result is: " + result);
} else if (mathchoice == '^') {
result = (int) Math.pow(number1, number2);
output.print("Result is: " + result);
System.out.println("Result is: " + result);
} else {
System.out.println("Wrong choice");
}
output.close();
System.out.println("Again?");
userchoice = choice.next().charAt(0);
}while (userchoice == 'j');
}
}
I added the output.close(), at the end of the lus. But I only get the last calculation.
答案1
得分: 1
你可以创建一个文件并直接写入内容,查看"java.io"类,如OutputStream、FileWriter等。
基本上你需要创建一个文件的引用,并使用"write"方法将内容写入。
// 在Windows下使用"c:\temp\my-file.log"
FileOutputStream fos = new FileOutputStream("/tmp/my-file.log");
fos.write("My log message".getBytes());
但如果可能的话,不要重复造轮子,使用LOG4J来记录你的日志。
LOG4J是一个广泛使用的库,可以让日志记录变得更简单。
而且为了管理项目的依赖,使用Maven。
创建一个Maven项目,在POM.XML中添加依赖,这将极大地简化你的工作。
英文:
You can create a file and write directly to it, see the "java.io" classes, such as OutputStream, FileWriter and etc.
You basically need to create a reference to the file and use the "write" method to write to it.
// on Windows use "c:\temp\my-file.log"
FileOutputStream fos = new FileOutputStream("/tmp/my-file.log");
fos.write("My log message".getBytes());
But if possible, do not reinvent the wheel and use LOG4J to record your logs.
LOG4J is a widely used library and it makes logging work much easier.
And to manage your project's dependencies, use Maven.
Create a maven project and add the dependencies in POM.XML, it will greatly simplify your life.
答案2
得分: 1
如果你想要获得与控制台中打印的完全相同的输出,即 System.out + System.in,一种方法是创建一个自定义的 InputStreamReader 并提供给 Scanner 使用,以及一个自定义的 PrintStream 来设置 System.out。这些自定义实现可以在读取/写入数据时将其写入文件中。
以下是一个示例:
```java
import java.io.*;
import java.nio.file.Paths;
import java.util.Scanner;
public class ScannerTest {
static boolean alive = true;
public static void main(String[] args){
int number1;
int number2;
char mathchoice;
int result;
char userchoice;
final File file = Paths.get("result.txt").toFile();
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream(file);
file.createNewFile();
System.setOut(new PrintStreamFileForwarder(System.out, fileOutputStream));
} catch (IOException e) {
e.printStackTrace();
}
Scanner choice = new Scanner(new InputStreamFileForwarder(System.in, fileOutputStream));
do {
System.out.println("Enter first number...");
number1 = choice.nextInt();
System.out.println("Math choice...");
mathchoice = choice.next().charAt(0);
System.out.println("Enter second number...");
number2 = choice.nextInt();
if (mathchoice == '+') {
result = number1 + number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '-') {
result = number1 - number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '*') {
result = number1 * number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '/') {
if (number2 == 0) {
throw new java.lang.ArithmeticException("Devided by zero not aloud");
} else {
result = number1 / number2;
System.out.println("Result is: " + result);
}
} else if (mathchoice == '%') {
result = number1 % number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '^') {
result = (int) Math.pow(number1, number2);
System.out.println("Result is: " + result);
} else {
System.out.println("Wrong choice");
}
System.out.println("Again?");
userchoice = choice.next().charAt(0);
} while (userchoice == 'j');
alive = false;
}
public static class InputStreamFileForwarder extends InputStreamReader {
private final FileOutputStream fileOutputStream;
public InputStreamFileForwarder(InputStream console, FileOutputStream fileOutputStream) {
super(console);
this.fileOutputStream = fileOutputStream;
}
@Override
public int read(char[] cbuf, int offset, int length) throws IOException {
int read = super.read(cbuf, offset, length);
if(read > 0) {
char[] allRead = new char[read];
System.arraycopy(cbuf, offset, allRead, 0, read);
fileOutputStream.write(new String(allRead).getBytes());
}
return read;
}
}
public static class PrintStreamFileForwarder extends PrintStream {
private final FileOutputStream fileOutputStream;
public PrintStreamFileForwarder(PrintStream console, FileOutputStream fileOutputStream) {
super(console);
this.fileOutputStream = fileOutputStream;
}
@Override
public void write(byte[] buf, int off, int len) {
super.write(buf, off, len);
try {
fileOutputStream.write(buf, off, len);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
英文:
If you want to get the exact same output as printed in the console, so System.out + System.in, one way to go about this is by creating a custom InputStreamReader to give to the Scanner, and a custom PrintStream to set System.out as. These custom implementations can then write to the file whenever they read/write data.
Here is an example:
import java.io.*;
import java.nio.file.Paths;
import java.util.Scanner;
public class ScannerTest {
static boolean alive = true;
public static void main(String[] args){
int number1;
int number2;
char mathchoice;
int result;
char userchoice;
final File file = Paths.get("result.txt").toFile();
FileOutputStream fileOutputStream = null;
try {
fileOutputStream = new FileOutputStream(file);
file.createNewFile();
System.setOut(new PrintStreamFileForwarder(System.out, fileOutputStream));
} catch (IOException e) {
e.printStackTrace();
}
Scanner choice = new Scanner(new InputStreamFileForwarder(System.in, fileOutputStream));
do {
System.out.println("Enter first number...");
number1 = choice.nextInt();
System.out.println("Math choice...");
mathchoice = choice.next().charAt(0);
System.out.println("Enter second number...");
number2 = choice.nextInt();
if (mathchoice == '+') {
result = number1 + number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '-') {
result = number1 - number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '*') {
result = number1 * number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '/') {
if (number2 == 0) {
throw new java.lang.ArithmeticException("Devided by zero not aloud");
} else {
result = number1 / number2;
System.out.println("Result is: " + result);
}
} else if (mathchoice == '%') {
result = number1 % number2;
System.out.println("Result is: " + result);
} else if (mathchoice == '^') {
result = (int) Math.pow(number1, number2);
System.out.println("Result is: " + result);
} else {
System.out.println("Wrong choice");
}
System.out.println("Again?");
userchoice = choice.next().charAt(0);
} while (userchoice == 'j');
alive = false;
}
public static class InputStreamFileForwarder extends InputStreamReader {
private final FileOutputStream fileOutputStream;
public InputStreamFileForwarder(InputStream console, FileOutputStream fileOutputStream) {
super(console);
this.fileOutputStream = fileOutputStream;
}
@Override
public int read(char[] cbuf, int offset, int length) throws IOException {
int read = super.read(cbuf, offset, length);
if(read > 0) {
char[] allRead = new char[read];
System.arraycopy(cbuf, offset, allRead, 0, read);
fileOutputStream.write(new String(allRead).getBytes());
}
return read;
}
}
public static class PrintStreamFileForwarder extends PrintStream {
private final FileOutputStream fileOutputStream;
public PrintStreamFileForwarder(PrintStream console, FileOutputStream fileOutputStream) {
super(console);
this.fileOutputStream = fileOutputStream;
}
@Override
public void write(byte[] buf, int off, int len) {
super.write(buf, off, len);
try {
fileOutputStream.write(buf, off, len);
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
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