java文件读写涉及到很多IO操作，读写方法较多，下面从字节流、字符流、节点流、处理流等方面进行介绍。
1.基本概念
输出流：程序->文件 输入流：文件->程序 字节流：一次读入或者读出是8位二进制字符流：一次读入或者读出是16位二进制流节点流：直接与数据源相连。处理流：在节点流上再套接一层，对一个已知流的连接和封装，构造方法带一个其他流对象作参数，通过所封装的流的功能调用实现数据读写。一个流对象经过其他流的多次包装，称为流的连接。
2.基本关系
红色标记的为与文件读写有关的类，带Buffered前缀的是处理流，会设置一个缓冲区，减少读写磁盘的次数。左边代表字符流，右边代表字节流。
3.例子
import java.io.*;
public class Exam1 {
public static void main(String[] args)
throws IOException {
String filename =
"file"+File.separator+
"test1.txt";
String outputfile =
"file"+File.separator+
"output.txt";
fileInpputStream(filename);
fileOutputStream();
bufferedInputStream(filename);
bufferedOutputStream(filename,outputfile);
readFileByChars(filename);
writeByFileReader(outputfile);
readByBufferedReader(filename);
writeByBufferedReader(outputfile);
}
/**
* 字节流：FileInputStream FileOutputStream
*/
public static void fileInpputStream(String fileName) {
FileInputStream fileInput =
null;
try {
File file =
new File(fileName);
if (!file.exists()) {
file.createNewFile();
}
byte[] buffer =
new byte[
1024];
fileInput =
new FileInputStream(file);
int byteread =
0;
while ((byteread = fileInput.read(buffer)) != -
1) {
System.out.write(buffer,
0, byteread);
}
}
catch (Exception e) {
}
finally {
try {
if (fileInput !=
null) {
fileInput.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
}
public static void fileOutputStream() {
FileOutputStream fop =
null;
File file;
String content =
"fileOutputStream";
try {
file =
new File(
"file"+File.separator+
"test1.txt");
fop =
new FileOutputStream(file,
true);
if (!file.exists()) {
file.createNewFile();
}
byte[] contentInBytes = content.getBytes();
fop.write(contentInBytes);
fop.flush();
fop.close();
}
catch (IOException e) {
e.printStackTrace();
}
finally {
try {
if (fop !=
null) {
fop.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 缓冲字节流：BufferedInputStream
* @throws IOException
*/
public static void bufferedInputStream(String filename)
throws IOException {
File file =
new File(filename);
FileInputStream fis =
new FileInputStream(file);
BufferedInputStream bis =
new BufferedInputStream(fis);
byte[] contents =
new byte[
1024];
int byteRead =
0;
String strFileContents;
try {
while((byteRead = bis.read(contents)) != -
1){
strFileContents =
new String(contents,
0,byteRead);
System.out.println(strFileContents);
}
}
catch (IOException e) {
e.printStackTrace();
}
bis.close();
}
/**
* 缓冲字节流：BufferedOutputStream
* @throws IOException
*/
public static void bufferedOutputStream(String filename,String outputfile)
throws IOException {
BufferedInputStream bis =
new BufferedInputStream(
new FileInputStream(filename));
BufferedOutputStream bos =
new BufferedOutputStream(
new FileOutputStream(outputfile));
int i;
do {
i = bis.read();
if (i != -
1) {
bos.write(i);
}
}
while (i != -
1);
bis.close();
bos.close();
}
/**
* 字符流:FileReader
*/
public static void readFileByChars(String fileName) {
FileReader reader =
null;
System.out.print(
"FileReader:");
try {
File file =
new File(fileName);
if (!file.exists()) {
file.createNewFile();
}
reader =
new FileReader(file);
char[] buffer =
new char[
1024];
int charread =
0;
while ((charread = reader.read(buffer)) != -
1) {
System.out.print(buffer);
}
}
catch (IOException e) {
}
finally {
try {
if (reader !=
null) {
reader.close();
}
}
catch (IOException e) {
e.printStackTrace();
}
}
}
/**
* 字符流：FileWriter
*/
public static void writeByFileReader(String output) {
try {
String data =
" This content will append to the end of the file";
File file =
new File(output);
if (!file.exists()) {
file.createNewFile();
}
FileWriter fileWritter =
new FileWriter(file.getName(),
true);
fileWritter.write(data);
fileWritter.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
/** 缓冲字符流 BufferedReader BufferedWriter
*
* @param fileName
*/
public static void readByBufferedReader(String fileName) {
System.out.println(
"BufferedReader:");
try {
File file =
new File(fileName);
BufferedReader bufread;
String read;
bufread =
new BufferedReader(
new FileReader(file));
while ((read = bufread.readLine()) !=
null) {
System.out.println(read);
}
bufread.close();
}
catch (FileNotFoundException ex) {
ex.printStackTrace();
}
catch (IOException ex) {
ex.printStackTrace();
}
}
public static void writeByBufferedReader(String output) {
try {
String content =
"This is the content to write into file";
File file =
new File(output);
if (!file.exists()) {
file.createNewFile();
}
FileWriter fw =
new FileWriter(file,
true);
BufferedWriter bw =
new BufferedWriter(fw);
bw.write(content);
bw.flush();
bw.close();
}
catch (IOException e) {
e.printStackTrace();
}
}
}
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