Java学习笔记——File类之文件管理和读写操作、下载图片

Java学习笔记——File类之文件管理和读写操作、下载图片

File类的总结：

1.文件和文件夹的创建

2.文件的读取

3.文件的写入

4.文件的复制（字符流、字节流、处理流）

5.以图片地址下载图片

文件和文件夹

相关函数

(boolean) mkdir() 创建此抽象路径名指定的目录

(boolean) mkdirs() 创建此抽象路径名指定的目录，包括所有必需但不存在的父目录。

(boolean) delete() 删除此抽象路径名表示的文件或目录

(boolean) createNewFile() 当不存在此路径名指定名称的文件时，创建一个新的空文件。

创建文件

public static void NewFile(String pathString) {
File file = new File(pathString);
if (!file.exists()) {
try {
if (file.createNewFile()) {
System.out.println("文件创建成功");
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
} else {
System.out.println("文件已存在");
}
}

创建文件夹

public static void NewFileBox(String pathString) {
File file2 = new File(pathString);
if (!file2.exists()) {
if (file2.mkdirs()) {
System.out.println("文件夹成功");
}
} else {
System.out.println("文件夹存在");
file2.delete();//销毁文件
}
}

应用：

public static void main(String[] args) {
NewFile("test/file.txt");
NewFileBox("test/a/a/a/a");
}

Writer写入文件

用FileWriter写入文件

public  static void ForFileWriter(String string,String fileName) {
File file = new File(fileName);
try {
FileWriter fWriter = new FileWriter(file);
fWriter.write(string);
fWriter.close();
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}

用BufferedWriter写入文件

public static void ForBufferedWriter(String string,String desFile) {
BufferedWriter bWriter = null;
try {
bWriter = new BufferedWriter(new FileWriter(new File(desFile)));
bWriter.write(string.toString());
bWriter.close();
} catch (Exception e) {
e.printStackTrace();
}
}

应用：

public static void main(String[] args) {
ForFileWriter("用FileWriter写入文件", "test/writer1.txt");
ForBufferedWriter("用BufferedWriter写入文件", "test/writer2.txt");
}

Reader读取文件

用FileReader读取文件

public static void testReadByReader(String fileName){
File file = new File(fileName);
FileReader fis = null;
try {
fis =  new FileReader(file);
char[] arr = new char[1024 * 1000 * 6];
int len = fis.read(arr);
String data = new String(arr, 0, len);
fis.close();
System.out.println(fileName+"中按FileReader读取的文件内容是：\n"+data);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

用FileInputStream读取文件

public static void testReadByInputStream(String fileName){
File file = new File(fileName);
FileInputStream fis = null;
try {
fis =  new FileInputStream(file);
byte[] arr = new byte[1024 * 1000 * 6];
int len = fis.read(arr);
String data = new String(arr, 0, len);
fis.close();
System.out.println(fileName+"中按FileInputStream读取的文件内容是：\n"+data);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}

用BufferedReader读取文件

public static void testReadByBufferedReader(String fileName) {
BufferedReader bReader = null;
String line = null;
StringBuffer buffer = new StringBuffer();
try {
bReader =new BufferedReader(new FileReader(new File(fileName)));
while ((line = bReader.readLine())!=null) {
buffer.append(line).append("\n");
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
System.out.println(fileName+"中按BufferedReader读取的文件内容是：\n"+buffer.toString());
}

应用：

public static void main(String[] args) {
testReadByInputStream("res/我.txt");
testReadByReader("res/我.txt");
testReadByBufferedReader("res/我.txt");
}

文件的复制操作

字符流复制

public static void FileCopy1(String readfile,String writeFile) {
try {
FileReader input = new FileReader(readfile);
FileWriter output = new FileWriter(writeFile);
int read = input.read();
while ( read != -1 ) {
output.write(read);
read = input.read();
}
input.close();
output.close();
} catch (IOException e) {
System.out.println(e);
}
}

字节流复制

public static void FileCopy2(String readfile,String writeFile) {
try {
FileInputStream input = new FileInputStream(readfile);
FileOutputStream output = new FileOutputStream(writeFile);
int read = input.read();
while ( read != -1 ) {
output.write(read);
read = input.read();
}
input.close();
output.close();
} catch (IOException e) {
System.out.println(e);
}
}

处理流复制

public static void FileCopy3(String readfile,String writeFile) {
BufferedReader bReader = null;
BufferedWriter bWriter = null;
String line = null;
try {
bReader = new BufferedReader(new FileReader(new File(readfile)));
bWriter = new BufferedWriter(new FileWriter(new File(writeFile)));
while ((line = bReader.readLine())!=null) {
bWriter.write(line);
bWriter.newLine();
}
bWriter.close();
bReader.close();
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}

应用：

public static void main(String[] args) {
FileCopy1("res/我.txt", "test/1.txt");
FileCopy2("res/我.txt", "test/2.txt");
FileCopy3("res/我.txt", "test/3.txt");
FileCopy2("res/me.jpg", "test/33.jpg");
}

以图片地址下载图片

读取给定图片文件的内容，用FileInputStream

public static byte[] mReaderPicture(String filePath) {
byte[] arr = null;
try {
File file = new File(filePath);
FileInputStream fReader = new FileInputStream(file);
arr = new byte[1024*100];
fReader.read(arr);
} catch (Exception  e) {
// TODO: handle exception
e.printStackTrace();
}
return arr;
}

根据byte数组，创建一张新图。

public static void mWriterPicture(String newFileName,byte[] b){
try {
File file = new File(newFileName);
FileOutputStream fStream = new FileOutputStream(file);
fStream.write(b);
fStream.close();
System.out.println("图片创建成功    "+b.length);
} catch (Exception e) {
// TODO: handle exception
}
}

获取指定网址的图片，返回其byte[]

public static byte[] mReaderPictureToInternet(String strUr1){
byte[] imgData = null;
URL url;
try {
url = new URL(strUr1);
URLConnection connection = url.openConnection();
int length = (int)connection.getContentLength();
InputStream is = connection.getInputStream();
if (length!=-1) {
imgData = new byte[length];
byte[] temp = new byte[500*1024];
int readLen = 0;
int destPos = 0;
while ((readLen = is.read(temp))>0) {
System.arraycopy(temp, 0, imgData, destPos, readLen);
//arraycopy(Object src, int srcPos, Object dest, int destPos, int length)
//从指定源数组中复制一个数组，复制从指定的位置开始，到目标数组的指定位置结束
destPos+=readLen;
}
}
return imgData;
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
return imgData;
}

直接获取指定网址的图片

public static void DownPictureToInternet(String filePath,String strUr1){
try {
URL url = new URL(strUr1);
InputStream fStream = url.openConnection().getInputStream();
int b = 0;
FileOutputStream fos = new FileOutputStream(new File(filePath));
while ((b=fStream.read())!=-1) {
fos.write(b);
}
fStream.close();
fos.close();
} catch (Exception e) {
e.printStackTrace();
}
}

应用：

public static void main(String[] args) {
mWriterPicture("test/1.jpg", mReaderPicture("res/me.jpg"));
mWriterPicture("test/2.jpg", mReaderPictureToInternet(
"http://pic2.desk.chinaz.com/file/201209/7/qinghimingyue4_p.jpg"));
DownPictureToInternet("test/下载.jpg",
"http://img3.100bt.com/upload/ttq/20130205/1360069663700.jpg");
}