Java从文本文件读取_向文本文件写入数据
通过Java从文本文件读取和向文本文件写入数据，了解流的基本的常用的方法。
示例代码：
package iotest;
import org.junit.Test;
import java.io.*;
/**
* Created with IntelliJ IDEA.
* User: ASUS
* Date: 14-7-21
* Time: 下午6:49
* To change this template use File | Settings | File Templates.
*/
public class IOTest {
/**
* 使用InputStream从文本文件中读取数据到ByteArrayOutputStream输出流中
* ByteArrayOutputStream
*/
@Test
public void test() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello.txt").getFile();
File file = new File(filePath);
InputStream inputStream = new FileInputStream(file);
ByteArrayOutputStream bos = new ByteArrayOutputStream();
int b;
while ((b = inputStream.read()) != -1) {
if (b == 10) {
System.out.println("new line");
}
bos.write(b);
}
byte[] result = bos.toByteArray();
System.out.println(new String(result));
}
/**
* 使用BufferedInputStream从文本文件读取数据
* BufferedInputStream
* 创建BufferedInputStream时，我们会通过它的构造函数指定某个输入流为参数。
* BufferedInputStream会将该输入流数据分批读取，
* 每次读取一部分到缓冲中；操作完缓冲中的这部分数据之后，再从输入流中读取下一部分的数据。
*
* @throws FileNotFoundException
*/
@Test
public void test9876() throws IOException {
int buffer_size = 12; //每次缓冲12个字节（做实验）
String filePath = this.getClass().getResource("/iotest/hello.txt").getFile();
BufferedInputStream in = new BufferedInputStream(new FileInputStream(filePath), buffer_size);
System.out.println(in.available());//45(可以读取到的总的字节数)
in.mark(50); //50为最大读取的字节的数量，当超过此数量后，mark失效
byte[] data = new byte[40]; //只读取40个字节
in.read(data);
System.out.println(new String(data));
byte[] data2 = new byte[5];
in.read(data2); //读取剩余的5个字节
System.out.println(new String(data2));
in.reset(); //重置此流
ByteArrayOutputStream bos = new ByteArrayOutputStream();
byte[] data3 = new byte[5];
while (in.read(data3) != -1) {
bos.write(data3);
}
System.out.println(bos.toString());
}
/**
* 使用BufferedReader从文本文件中读取数据（缓冲输入流）
* BufferedReader
* InputStreamReader
*
* @throws IOException
*/
@Test
public void test2323() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello.txt").getFile();
File file = new File(filePath);
InputStreamReader read = new InputStreamReader(new FileInputStream(file));
BufferedReader bufferedReader = new BufferedReader(read);
String line = null;
StringBuilder builder = new StringBuilder();
while ((line = bufferedReader.readLine()) != null) {
builder.append(line); //缓存读到的数据
}
System.out.println(builder.toString()); //打印出的数据没有换行（没有读取换行符）
}
/**
* ByteArrayInputStream
* 把字节数组转换为字节流对象，以便提供读取接口read方法
* read()的作用是从字节流中“读取下一个字节”。
* read(byte[] buffer, int offset, int length)的作用是从字节流读取字节数据，并写入到字节数组buffer中。
*/
@Test
public void test23233() {
byte[] ArrayLetters = {
0x61, 0x62, 0x63, 0x64, 0x65, 0x66, 0x67, 0x68, 0x69, 0x6A, 0x6B, 0x6C, 0x6D, 0x6E, 0x6F,
0x70, 0x71, 0x72, 0x73, 0x74, 0x75, 0x76, 0x77, 0x78, 0x79, 0x7A
};
ByteArrayInputStream bais = new ByteArrayInputStream(ArrayLetters);
int LEN = 5;
for (int i = 0; i < LEN; i++) {
// 若能继续读取下一个字节，则读取下一个字节
if (bais.available() >= 0) {
// 读取“字节流的下一个字节”
int tmp = bais.read();
System.out.printf("%d : 0x%s\n", i, Integer.toHexString(tmp));
}
}
}
/**
* 使用FileWriter向文本文件中写入数据
* windows中\r\n换行
*
* @throws IOException
*/
@Test
public void test8766() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello2.txt").getFile();
//直接调用构造方法，传递写入路径。FileWriter类的构造方法有五个。
FileWriter writer = new FileWriter(filePath);
//FileWriter类的Write（）方法向文件中写入字符。
writer.write("Hello!\r\n");
writer.write("Thisis my first text file,\r\n");
writer.write("I'mvery happy!\r\n");
writer.write("EveryDay is a new Day!\r\n");
writer.write("我爱我家！");
writer.close();
}
/**
* 使用BufferedWriter向文本文件中写入数据
* windows中\r\n换行
*
* @throws IOException
*/
@Test
public void test87a6() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello2.txt").getFile();
BufferedWriter out = new BufferedWriter(new FileWriter(filePath));
//FileWriter类的Write（）方法向文件中写入字符。
out.write("NewHello!");
out.newLine();
out.write("This is Buffer Writer范例,");
out.newLine();
out.write("keepalone");
out.newLine();
out.close();
}
/**
* 使用OutputStream想文本文件写入数据
*
* @throws IOException
*/
@Test
public void test87559() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello2.txt").getFile();
OutputStream out = new FileOutputStream(filePath);
out.write("abcdefg".getBytes());
out.write("\r\n".getBytes()); //换行
out.write("123456".getBytes());
}
/**
* OutputStreamWriter包装字节流输出流
* 向文本文件写入数据
*
* @throws IOException
*/
@Test
public void test86() throws IOException {
String filePath = this.getClass().getResource("/iotest/hello2.txt").getFile();
OutputStream out = new FileOutputStream(filePath);
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(out); //字节流和字符流的转换
BufferedWriter bufferedWriter = new BufferedWriter(outputStreamWriter);
bufferedWriter.write("NewHello!");
bufferedWriter.newLine();
bufferedWriter.write("This is Buffer Writer范例,");
bufferedWriter.newLine();
bufferedWriter.write("keepalone");
bufferedWriter.newLine();
bufferedWriter.close();
}
}
参考：http://www.cnblogs.com/skywang12345/p/io_12.html
import java.io.BufferedOutputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class Main {
/**
* Prints some data to a file
*/
public void writeToFile(String filename) {
BufferedOutputStream bufferedOutput = null;
try {
//Construct the BufferedOutputStream object
bufferedOutput = new BufferedOutputStream(new FileOutputStream(filename));
//Start writing to the output stream
bufferedOutput.write("Line one".getBytes());
bufferedOutput.write("\n".getBytes()); //new line, you might want to use \r\n if you're on Windows
bufferedOutput.write("Line two".getBytes());
bufferedOutput.write("\n".getBytes());
//prints the character that has the decimal value of 65
bufferedOutput.write(65);
} catch (FileNotFoundException ex) {
ex.printStackTrace();
} catch (IOException ex) {
ex.printStackTrace();
} finally {
//Close the BufferedOutputStream
try {
if (bufferedOutput != null) {
bufferedOutput.flush();
bufferedOutput.close();
}
} catch (IOException ex) {
ex.printStackTrace();
}
}
}
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
new Main().writeToFile("myFile.txt");
}
}
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