在Java中,似乎有不同的方式来读取和写入文件数据。
我想从一个文件读取ASCII数据。可能的方式和它们的区别是什么?
在Java中,似乎有不同的方式来读取和写入文件数据。
我想从一个文件读取ASCII数据。可能的方式和它们的区别是什么?
当前回答
以下是三种工作和测试的方法:
使用BufferedReader
package io;
import java.io.*;
public class ReadFromFile2 {
public static void main(String[] args)throws Exception {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
BufferedReader br = new BufferedReader(new FileReader(file));
String st;
while((st=br.readLine()) != null){
System.out.println(st);
}
}
}
使用扫描仪
package io;
import java.io.File;
import java.util.Scanner;
public class ReadFromFileUsingScanner {
public static void main(String[] args) throws Exception {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
Scanner sc = new Scanner(file);
while(sc.hasNextLine()){
System.out.println(sc.nextLine());
}
}
}
使用FileReader
package io;
import java.io.*;
public class ReadingFromFile {
public static void main(String[] args) throws Exception {
FileReader fr = new FileReader("C:\\Users\\pankaj\\Desktop\\test.java");
int i;
while ((i=fr.read()) != -1){
System.out.print((char) i);
}
}
}
使用Scanner类读取整个文件,而不使用循环
package io;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReadingEntireFileWithoutLoop {
public static void main(String[] args) throws FileNotFoundException {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
Scanner sc = new Scanner(file);
sc.useDelimiter("\\Z");
System.out.println(sc.next());
}
}
其他回答
以下是三种工作和测试的方法:
使用BufferedReader
package io;
import java.io.*;
public class ReadFromFile2 {
public static void main(String[] args)throws Exception {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
BufferedReader br = new BufferedReader(new FileReader(file));
String st;
while((st=br.readLine()) != null){
System.out.println(st);
}
}
}
使用扫描仪
package io;
import java.io.File;
import java.util.Scanner;
public class ReadFromFileUsingScanner {
public static void main(String[] args) throws Exception {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
Scanner sc = new Scanner(file);
while(sc.hasNextLine()){
System.out.println(sc.nextLine());
}
}
}
使用FileReader
package io;
import java.io.*;
public class ReadingFromFile {
public static void main(String[] args) throws Exception {
FileReader fr = new FileReader("C:\\Users\\pankaj\\Desktop\\test.java");
int i;
while ((i=fr.read()) != -1){
System.out.print((char) i);
}
}
}
使用Scanner类读取整个文件,而不使用循环
package io;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;
public class ReadingEntireFileWithoutLoop {
public static void main(String[] args) throws FileNotFoundException {
File file = new File("C:\\Users\\pankaj\\Desktop\\test.java");
Scanner sc = new Scanner(file);
sc.useDelimiter("\\Z");
System.out.println(sc.next());
}
}
这里有另一种不使用外部库的方法:
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
public String readFile(String filename)
{
String content = null;
File file = new File(filename); // For example, foo.txt
FileReader reader = null;
try {
reader = new FileReader(file);
char[] chars = new char[(int) file.length()];
reader.read(chars);
content = new String(chars);
reader.close();
} catch (IOException e) {
e.printStackTrace();
} finally {
if(reader != null){
reader.close();
}
}
return content;
}
如果这是关于结构的简单性,请使用Java kiss:
import static kiss.API.*;
class App {
void run() {
String line;
try (Close in = inOpen("file.dat")) {
while ((line = readLine()) != null) {
println(line);
}
}
}
}
我编写的这段代码对于非常大的文件要快得多:
public String readDoc(File f) {
String text = "";
int read, N = 1024 * 1024;
char[] buffer = new char[N];
try {
FileReader fr = new FileReader(f);
BufferedReader br = new BufferedReader(fr);
while(true) {
read = br.read(buffer, 0, N);
text += new String(buffer, 0, read);
if(read < N) {
break;
}
}
} catch(Exception ex) {
ex.printStackTrace();
}
return text;
}
这基本上与Jesus Ramos的回答完全相同,除了使用File而不是FileReader加上迭代来逐级遍历文件的内容。
Scanner in = new Scanner(new File("filename.txt"));
while (in.hasNext()) { // Iterates each line in the file
String line = in.nextLine();
// Do something with line
}
in.close(); // Don't forget to close resource leaks
... 抛出FileNotFoundException