IO流技术：缓冲大法好，10行代码爬取网页
本篇介绍缓冲流和转换流的作用，最后结合在一起，实现一个爬取网页内容的小程序。
一、缓冲流
1、概述：Buffered…
- 字节/字符缓冲流可以很大程度提高性能，虚拟机内部就有，默认缓冲区大小为8K，可以自己指定。
- 不管怎么处理，底层都是节点流：文件节点流、字节数组节点流、网络流…
- 可以直接释放BufferdInputStream
2、实例：文件字符输出
主程序：
public static void main(String[] args){
//1、创建源
File src = new File("dest.txt");
//2、选择字符流
BufferedWriter writer=null;
try {
//操作内容...
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
操作方法一：
writer = new BufferedWriter(new FileWriter(src));
String msg = "Study is so easy周百青";
char[] datas = msg.toCharArray(); //字符串转字符数组
writer.write(datas,0,datas.length);
操作方法二：
writer = new BufferedWriter(new FileWriter(src));
String msg = "Study is so easy周百青";
writer.write(msg);
writer.write("add");
writer.flush();
操作方法三：
writer = new BufferedWriter(new FileWriter(src));
writer.append("Study is so easy\r\n").append("周百青");
操作方法四：
writer = new BufferedWriter(new FileWriter(src));
writer.append("Study is so easy");
writer.newLine(); //新增换行符
writer.append("周百青");
writer.flush();
二、转换流
1、概述：InputStreamReader&OutputStreamWriter
- 将字节流（纯文本）转换为字符流，方便处理
- 可以指定字符集，以防出现乱码
- InputStreamReader 字节流到字符流
OutputStreamWriter字符流到字节流
2、实例：控制台看转换过程
public class ConvertTest {
public static void main(String[] args) {
//操作System.in和System.out
//凡是字符串的地方，都建议加上缓冲
try(BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(System.out));){
//循环获取键盘的输入（exit退出）,并输出此内容
String msg = "";
while(!msg.equals("exit")){
msg=reader.readLine(); //循环逐行读取
writer.write(msg); //循环写出
writer.newLine(); //换行
writer.flush(); //强制刷新，防止内容驻留在管道中
}
}catch(Exception e){
System.out.println("操作异常！");
}
}
}
结果
三、爬取网页（百度首页为例）
10行代码
public static void main(String[] args) {
try(BufferedReader reader = new BufferedReader(new InputStreamReader(new URL("http://www.baidu.com").openStream(),"UTF-8"));
BufferedWriter writer = new BufferedWriter(new OutputStreamWriter(new FileOutputStream("baidu.html"),"UTF-8"));){
String msg;
while((msg=reader.readLine())!=null){
writer.write(msg);
writer.newLine(); }
writer.flush();
}catch(Exception e){
System.out.println("操作异常！"); } }
源码
public class ConvertTest2 {
public static void main(String[] args) {
try(BufferedReader reader =
//加上缓冲
new BufferedReader(
//转为字符操作
new InputStreamReader(
//获取网络流，最好指定字符集(默认跟工程字符集一致可能会乱)
new URL("http://www.baidu.com").openStream(),"UTF-8"));
BufferedWriter writer =
new BufferedWriter(
new OutputStreamWriter(
new FileOutputStream("baidu.html"),"UTF-8"));){
//读取
String msg;
while((msg=reader.readLine())!=null){
//System.out.print(msg);
writer.write(msg);
writer.newLine();
}
writer.flush();
}catch(Exception e){
System.out.println("操作异常！");
}
}
}
结果
<!DOCTYPE html>
<!--STATUS OK--><html> <head><meta http-equiv=content-type content=text/html;charset=utf-8><meta http-equiv=X-UA-Compatible content=IE=Edge><meta content=always name=referrer><link rel=stylesheet type=text/css href=http://s1.bdstatic.com/r/www/cache/bdorz/baidu.min.css><title>百度一下，你就知道</title></head> <body link=#0000cc> <div id=wrapper> <div id=head> <div class=head_wrapper> <div class=s_form> <div class=s_form_wrapper> <div id=lg> <img hidefocus=true src=//www.baidu.com/img/bd_logo1.png width=270 height=129> 