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Java读取文件-BufferedReader/FileReader/InputStreamReader/FileInputStream的关系和区别
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一、Java读取和存储文件数据流Java读取文件，实际是将文件中的字节流转换成字符流输出到屏幕的过程 这里面涉及到两个类：InputStreamReader和OutputStreamWriterInputStreamReader：将字节流转换成字符流OutputStreamWriter：将字符流转换成字节流 
InputStreamReader继承Reader类OutputStreamWriter继承Writer类 二、BufferedReader/FileReader/InputStreamReaderReader是用于将文件中的内容读出来；Writer用于将字符写入到文件中去。Reader是用于读取字符流的抽象类1、BufferedReader/FileReader/InputStreamReader的继承关系如下：
所以通过BufferedReader/FileReader/InputStreamReader这三个方法读出来的文件，都可以直接输出字符2、BufferedReader/FileReader/InputStreamReader的使用方法及区别
InputStreamReader：可以指定字符编码格式,入参传递InputStream对象InputStream对象定义方法有两种。System.in或FileInputStream对象System.in：读取控制台的输入内容FileInputStream：可通过文件路径名pathname或File对象实例化InputStreamReader inputstreamreader1=new InputStreamReader(System.in);
InputStreamReader inputstreamreader2=new InputStreamReader(new FileInputStream("/opt/xxx"));
InputStreamReader inputstreamreader3=new InputStreamReader(new FileInputStream(new File("/opt/xxx")));
FileReader：入参直接传递文件pathname或File对象FileReader是InputStreamReader的子类，不能指定字符编码，其他与InputStreamReader基本类似FileReader f1=new FileReader("/opt/xxx.txt");
FileReader f2=new FileReader(new File("/opt/xxx.txt"));
BufferedReader：入参有Reader对象和缓冲区大小（可不写）从缓存区中读取字符流，提高效率；缓冲区大小：默认8192，默认不需要传递建议都要用这个类去读取文件BufferedReader buffered_filereader=new BufferedReader(new FileReader(filename));
BufferedReader buffered_inputstreamreader=new BufferedReader(new InputStreamReader(fileinputstream));
三、FileInputStream所有字节输入流的超类，用于字节流的读取。上面已经讲了，应用在实例化InputStreamReader对象时的一种入参 可以传递文件路径名pathname或File对象实例化 四、读取文件BufferedReader对象使用readLine()方法判断字符串是否为null判断是否为文件末尾String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
Reader子类InputSteamReader和FileReader使用read()方法判断是否为-1，来判断是否为文件末尾int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
五、Java代码1、InputSteamReaderString filename="/opt/xxx.log";FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
int i;
while ((i=inputstreamreader.read())!=-1){
System.out.print((char)i);
}
2、FileReaderString filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
3、BufferedReader（入参FileReader）String filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
BufferedReader buffered_filereader=new BufferedReader(filereader);
String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
4、BufferedReader（入参InputStreamReader）String filename="/opt/xxx.log";
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
BufferedReader buffered_inputstreamreader=new BufferedReader(inputstreamreader);
String read;
while((read=buffered_inputstreamreader.readLine())!=null){
System.out.println(read);
}
Reader是用于将文件中的内容读出来；Writer用于将字符写入到文件中去。
Reader是用于读取字符流的抽象类
1、BufferedReader/FileReader/InputStreamReader的继承关系如下：
所以通过BufferedReader/FileReader/InputStreamReader这三个方法读出来的文件，都可以直接输出字符
2、BufferedReader/FileReader/InputStreamReader的使用方法及区别
InputStreamReader：可以指定字符编码格式,入参传递InputStream对象
InputStream对象定义方法有两种。System.in或FileInputStream对象
System.in：读取控制台的输入内容
FileInputStream：可通过文件路径名pathname或File对象实例化
InputStreamReader inputstreamreader1=new InputStreamReader(System.in);
InputStreamReader inputstreamreader2=new InputStreamReader(new FileInputStream("/opt/xxx"));
InputStreamReader inputstreamreader3=new InputStreamReader(new FileInputStream(new File("/opt/xxx")));
FileReader：入参直接传递文件pathname或File对象
FileReader是InputStreamReader的子类，不能指定字符编码，其他与InputStreamReader基本类似
FileReader f1=new FileReader("/opt/xxx.txt");
FileReader f2=new FileReader(new File("/opt/xxx.txt"));
BufferedReader：入参有Reader对象和缓冲区大小（可不写）
从缓存区中读取字符流，提高效率；缓冲区大小：默认8192，默认不需要传递
建议都要用这个类去读取文件
BufferedReader buffered_filereader=new BufferedReader(new FileReader(filename));
BufferedReader buffered_inputstreamreader=new BufferedReader(new InputStreamReader(fileinputstream));
三、FileInputStream所有字节输入流的超类，用于字节流的读取。上面已经讲了，应用在实例化InputStreamReader对象时的一种入参 可以传递文件路径名pathname或File对象实例化 四、读取文件BufferedReader对象使用readLine()方法判断字符串是否为null判断是否为文件末尾String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
Reader子类InputSteamReader和FileReader使用read()方法判断是否为-1，来判断是否为文件末尾int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
五、Java代码1、InputSteamReaderString filename="/opt/xxx.log";FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
int i;
while ((i=inputstreamreader.read())!=-1){
System.out.print((char)i);
}
2、FileReaderString filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
3、BufferedReader（入参FileReader）String filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
BufferedReader buffered_filereader=new BufferedReader(filereader);
String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
4、BufferedReader（入参InputStreamReader）String filename="/opt/xxx.log";
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
BufferedReader buffered_inputstreamreader=new BufferedReader(inputstreamreader);
String read;
while((read=buffered_inputstreamreader.readLine())!=null){
System.out.println(read);
}
BufferedReader对象使用readLine()方法判断字符串是否为null判断是否为文件末尾
String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
Reader子类InputSteamReader和FileReader使用read()方法判断是否为-1，来判断是否为文件末尾
int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
五、Java代码1、InputSteamReaderString filename="/opt/xxx.log";FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
int i;
while ((i=inputstreamreader.read())!=-1){
System.out.print((char)i);
}
2、FileReaderString filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
3、BufferedReader（入参FileReader）String filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
BufferedReader buffered_filereader=new BufferedReader(filereader);
String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
4、BufferedReader（入参InputStreamReader）String filename="/opt/xxx.log";
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
BufferedReader buffered_inputstreamreader=new BufferedReader(inputstreamreader);
String read;
while((read=buffered_inputstreamreader.readLine())!=null){
System.out.println(read);
}
String filename="/opt/xxx.log";FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
int i;
while ((i=inputstreamreader.read())!=-1){
System.out.print((char)i);
}
String filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
int i;
while ((i=filereader.read())!=-1){
System.out.print((char)i);
}
String filename="/opt/xxx.log";FileReader filereader=new FileReader(filename);
BufferedReader buffered_filereader=new BufferedReader(filereader);
String read;
while((read=buffered_filereader.readLine())!=null){
System.out.println(read);
}
String filename="/opt/xxx.log";
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
BufferedReader buffered_inputstreamreader=new BufferedReader(inputstreamreader);
String read;
while((read=buffered_inputstreamreader.readLine())!=null){
System.out.println(read);
}
