MINA源码分析---可移植的操作系统分界符(换行符)

package org.apache.mina.filter.codec.textline;

import java.io.ByteArrayOutputStream;
import java.io.PrintWriter;

/**
* A delimiter分界符 which is appended to the end of a text line, such as
* <tt>CR/LF</tt>. This class defines default delimiters for various
* OS :
* <ul>
* <li><b>Unix/Linux</b> : LineDelimiter.UNIX ("\n")</li>
* <li><b>Windows</b> : LineDelimiter.WINDOWS ("\r\n")</li>
* <li><b>MAC</b> : LineDelimiter.MAC ("\r")</li>
* </ul>
*
*/
public class LineDelimiter {
/** the line delimiter constant of the current O/S. */
public static final LineDelimiter DEFAULT;

/** Compute the default delimiter on the current OS
* 计算出本操作系统上默认的分界符(通常说的换行符)
*/
static {
//建立一个字节数组输出流
ByteArrayOutputStream bout = new ByteArrayOutputStream();
//建立一个打印流,参数1是一个标准输出流,决定输出到哪个地方,参数2指定是否刷新输出(不缓冲)
PrintWriter out = new PrintWriter(bout, true);
out.println();//输出一个“换行符”到bout中
DEFAULT = new LineDelimiter(new String(bout.toByteArray()));
}

/**
* A special line delimiter which is used for auto-detection of
* EOL in {@link TextLineDecoder}. If this delimiter is used,
* {@link TextLineDecoder} will consider both <tt>'\r'</tt> and
* <tt>'\n'</tt> as a delimiter.
*/
public static final LineDelimiter AUTO = new LineDelimiter("");

/**
* The CRLF line delimiter constant (<tt>"\r\n"</tt>)
*/
public static final LineDelimiter CRLF = new LineDelimiter("\r\n");

/**
* The line delimiter constant of UNIX (<tt>"\n"</tt>)
*/
public static final LineDelimiter UNIX = new LineDelimiter("\n");

/**
* The line delimiter constant of MS Windows/DOS (<tt>"\r\n"</tt>)
*/
public static final LineDelimiter WINDOWS = CRLF;

/**
* The line delimiter constant of Mac OS (<tt>"\r"</tt>)
*/
public static final LineDelimiter MAC = new LineDelimiter("\r");

/**
* The line delimiter constant for NUL-terminated text protocols
* such as Flash XML socket (<tt>"\0"</tt>)
*/
public static final LineDelimiter NUL = new LineDelimiter("\0");

/** Stores the selected Line delimiter */
private final String value;

/**
* Creates a new line delimiter with the specified <tt>value</tt>.
*/
public LineDelimiter(String value) {
if (value == null) {
throw new IllegalArgumentException("delimiter");
}

this.value = value;
}

/**
* Return the delimiter string.
*/
public String getValue() {
return value;
}

/**
* {@inheritDoc}
*/
@Override
public int hashCode() {
return value.hashCode();
}

/**
* {@inheritDoc}
* 不仅比较地址，还比较值
*/
@Override
public boolean equals(Object o) {
if ( this == o) {
return true;
}

if (!(o instanceof LineDelimiter)) {
return false;
}

LineDelimiter that = (LineDelimiter) o;

return this.value.equals(that.value);
}

/**
* {@inheritDoc}
*/
@Override
public String toString() {
if (value.length() == 0) {
return "delimiter: auto";
} else {
StringBuilder buf = new StringBuilder();
buf.append("delimiter:");

for (int i = 0; i < value.length(); i++) {
buf.append(" 0x");
//整数转换成16进制字符
buf.append(Integer.toHexString(value.charAt(i)));
}

return buf.toString();
}
}
}