Java 文件读写操作

1. 对于文本文件的读写

1.1. 读取文本文件

package com.martinwangjun.io;

import java.io.FileReader;
import java.io.IOException;

public class FileReaderTest {

// 注意，需要抛出IOException或在代码中使用try...catch...
public static void main(String[] args) throws IOException
{
// 对于eclipse，注意实际的路径，我们这里用了package
FileReader fileReader = new FileReader(
"./src/com/martinwangjun/io/FileReaderTest.java");
char[] buffer = new char[1024];
int hasReader = 0;
while ((hasReader = fileReader.read(buffer)) > 0) {
System.out.println(new String(buffer, 0, hasReader));
}
// 这里其实写得不严谨，最好使用Java 7的AutoClosable
// 或者finally中关闭资源
fileReader.close();
}
}

1.2. 写入文本文件

package com.martinwangjun.io;

import java.io.FileWriter;

public class FileWriterTest {

public static void main(String[] args) {
// 这里用来Java 7的AutoClosable的特性，会自动关闭资源。
try(FileWriter fileWriter = new FileWriter(
"src/com/martinwangjun/io/poem.txt")) {
fileWriter.write("先令\r\n");
} catch (Exception ex) {
ex.printStackTrace();
}
}

}

2. 二进制文件

package com.martinwangjun.io;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

public class FileOutputStreamTest {

public static void main(String[] args) throws IOException{
// 使用了Java 7的自动关闭机制
try(FileInputStream fileInputStream = new FileInputStream(
"src/com/martinwangjun/io/01.jpg");
FileOutputStream fileOutputStream = new FileOutputStream(
"src/com/martinwangjun/io/02.jpg");
){
byte[] buffer = new byte[1024];
int hasRead = 0;
while ((hasRead = fileInputStream.read(buffer)) > 0) {
fileOutputStream.write(buffer, 0, hasRead);
}
buffer = "Powered By Martin".getBytes();
fileOutputStream.write(buffer, 0,
"Powered By Martin".length());
}
catch (Exception ex) {
ex.printStackTrace();
}
}
}

3. 利用包装流

3.1. 利用PrintStream流来包装FileOutputStream

package com.martinwangjun.io;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;

public class PrintStreamTest {

public static void main(String[] args) throws IOException {

try(
FileOutputStream fos = new FileOutputStream(
"src/com/martinwangjun/io/test.txt");
PrintStream ps = new PrintStream(fos))
{
// 这样的话不用考虑怎么写入文件，当成普通的打印一样使用
ps.println("普通字符串");
ps.println(new PrintStreamTest());
}
catch (Exception ex) {
ex.printStackTrace();
}
}
}

4. 获取用户输入

package com.martinwangjun.io;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class KeyinTest {

public static void main(String[] args) throws IOException{
InputStreamReader reader = null;
BufferedReader bufferedReader = null;
try {
reader = new InputStreamReader(System.in);
bufferedReader = new BufferedReader(reader);

String line = null;
while ((line = bufferedReader.readLine()) != null) {
if(line.toLowerCase().equals("exit")){
System.exit(1);
}
System.out.println(line);
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
if(reader != null){
try {
reader.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
if(bufferedReader != null){
try {
bufferedReader.close();
} catch (Exception ex) {
ex.printStackTrace();
}
}
}
}

}

5. 添加而不是覆盖

package com.martinwangjun.io;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.FileOutputStream;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;

public class BufferedWriteTextFile {

public static void main(String[] args) throws Exception {
try (
// 这里用了true，表示可以Append
BufferedWriter bufferedWriter = new BufferedWriter(
new OutputStreamWriter(
new FileOutputStream(
"src/com/martinwangjun/io/output.txt", true)));
BufferedReader bufferedReader = new BufferedReader(
new InputStreamReader(System.in)))
{
String line = null;
while( ! (line = bufferedReader.readLine()).equals("")){
bufferedWriter.write(line);
bufferedWriter.newLine();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}