java io主要有5个核心类和一个核心接口：
五个核心类：File、InputStream、OutputStream、Reader、Writer；
一个核心接口： Serializable
File类是唯一一个与文件本身操作相关的类（创建、删除）；
File类
构造方法：
public File(String pathname) { //设置完整路径
if (pathname == null) {
throw new NullPointerException();
}
this.path = fs.normalize(pathname);
this.prefixLength = fs.prefixLength(this.path);
}
public File(String parent, String child) {// 设置父路径和子路径
if (child == null) {
throw new NullPointerException();
}
if (parent != null) {
if (parent.equals("")) {
this.path = fs.resolve(fs.getDefaultParent(),
fs.normalize(child));
} else {
this.path = fs.resolve(fs.normalize(parent),
fs.normalize(child));
}
} else {
this.path = fs.normalize(child);
}
this.prefixLength = fs.prefixLength(this.path);
}
创建文件：
public boolean createNewFile() throws IOException {
SecurityManager security = System.getSecurityManager();
if (security != null) security.checkWrite(path);
if (isInvalid()) {
throw new IOException("Invalid file path");
}
return fs.createFileExclusively(path);
}
public boolean delete() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkDelete(path);
}
if (isInvalid()) {
return false;
}
return fs.delete(this);
}
public boolean delete() {
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkDelete(path);
}
if (isInvalid()) {
return false;
}
return fs.delete(this);
}
package just;
import java.io.File;
import java.io.IOException;
public class StringBase{
public static void main(String args[]) throws IOException{
File myFile =new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
/*文件不能重名、重复、父目录要存在，路径的分隔符为“\\”；
最合理的路径创建为：
file.separator,（其实若有父路径要判断是否存在父路径）
*/
if(myFile.createNewFile())
System.out.println("创建OK");
else
System.out.println("创建NG");
if(myFile.exists()){
System.out.println("执行删除");
myFile.delete();
System.out.println("删除OK");
}
else{
System.out.println("创建"+myFile.createNewFile());
}
}
}
父路径
public String getParent() {
int index = path.lastIndexOf(separatorChar);
if (index < prefixLength) {
if ((prefixLength > 0) && (path.length() > prefixLength))
return path.substring(0, prefixLength);
return null;
}
return path.substring(0, index);
}
public boolean mkdir() { 创建1级文件夹
SecurityManager security = System.getSecurityManager();
if (security != null) {
security.checkWrite(path);
}
if (isInvalid()) {
return false;
}
return fs.createDirectory(this);
}
public boolean mkdirs() { 创建多级文件夹
if (exists()) {
return false;
}
if (mkdir()) {
return true;
}
File canonFile = null;
try {
canonFile = getCanonicalFile();
} catch (IOException e) {
return false;
}
File parent = canonFile.getParentFile();
return (parent != null && (parent.mkdirs() || parent.exists()) &&
canonFile.mkdir());
}
File类的文件属性
包含文件的属性信息，如建立时间，修改时间等；
操作文件的输入输出，采用字节流和字符流；
字节流\字符流
字节流：InputStream\OutPutStream;
字符流：reader/writer
字节流
OutputStream类：
public abstract class OutputStream implements Closeable, Flushable{
public void flush() throws IOException {
}
public void close() throws IOException {
}
}
//实现了两个接口
public interface Closeable extends AutoCloseable {
public void close() throws IOException;
...
}
public interface AutoCloseable {
void close() throws Exception;
} //自动关闭接口
public interface Flushable {
void flush() throws IOException; //请空
}
public abstract void write(int b) throws IOException;//输出单个字节数组
public void write(byte b[]) throws IOException {
write(b, 0, b.length);
}
public void write(byte b[], int off, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if ((off < 0) || (off > b.length) || (len < 0) ||
((off + len) > b.length) || ((off + len) < 0)) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return;
}
for (int i = 0 ; i < len ; i++) {
write(b[off + i]);
}
}
package StringBase;
import java.io.File;
import java.io.FileOutputStream;
import java.io.OutputStream;
import java.lang.reflect.Method;
public class Base {
public static void main(String args[]) throws Exception {
File file=new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
if(!file.getParentFile().exists())
file.getParentFile().mkdirs();//判断是否存在目录
OutputStream output=new FileOutputStream(file,true);
//true 代表追加，不写代表覆盖
String str="dream"+"\\r";
byte[] b=str.getBytes();\\字符串转化为字节数组
output.write(b,1,3);//输出后会覆盖
output.close();//关闭
}
}
InputStream
public abstract int read() throws IOException;
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
public abstract int read() throws IOException;
public int read(byte b[]) throws IOException {
return read(b, 0, b.length);
}
package StringBase;
import java.io.*;
public class Base {
public static void main(String args[]) throws Exception {
File file=new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
if(file.exists())
{
InputStream input=new FileInputStream(file);
int temp=0;
while ((temp=input.read())!=-1){
System.out.println((char)(temp));
}
input.close();
}
}
}
字符流
package StringBase;
import java.io.*;
public class Base {
public static void main(String args[]) throws Exception {
File file=new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
if(!file.getParentFile().exists()){
file.getParentFile().mkdirs();
}
Writer out=new FileWriter(file);
String str="hello world";
out.write(str);
out.flush();
//out.close();
}
}
package StringBase;
import java.io.*;
public class Base {
public static void main(String args[]) throws Exception {
File file=new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
if(file.exists())
{
Reader in=new FileReader(file);
int temp=0;
while ((temp=in.read())!=-1){
System.out.println((char)temp);
}
}
}
}
字节流和字符流
1、字节流可以直接与终端交流，而字符流通过缓冲区与终端进行交互；
2、字符流不使用关闭功能时（close()），其不会强制把缓冲区的数据清空，即数据不会写入到文件中去，除非采用flush()方法；
3、字节数据处理使用较多，比如图片，音乐电影；字符流数据处理中文时较为方便；
转换流
字符流需要缓冲区，但是字符流可以直接输出字符串，故需要将字节流转换为字符流；
public class InputStreamReader extends Reader {...}
public class OutputStreamWriter extends Writer {...)
package StringBase;
import java.io.*;
public class Base {
public static void main(String args[]) throws Exception {
File file=new File("D:"+File.separator+"Life"+File.separator+"Test.txt");
if(!file.getParentFile().exists())
file.getParentFile().mkdirs();
OutputStream output =new FileOutputStream(file);
Writer out=new OutputStreamWriter(output);
out.write("hello world");
out.close();
}
}
