java读取流数据时，字节缓存数组，第一次读取时，是否读满，才进行下次读取？？

Z时代
2024-01-10
分类：IT

使用缓存字节数组读取java字节流时，第一次读取是，读满缓存字节数组大小，才进行下次读取，还是随机读一个小于数组大小的值，再进行下次读取？？？

读取本地文件时，首次读取读满整个字节数组，在进行下次读取。

package com.lyf.test;
import java.io.File;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.InputStream;
import org.junit.Test;
public class ReadFile {
    @Test
    public void readTxt() {
        InputStream is = null;
        String path = this.getClass().getClassLoader().getResource("abc.txt")
                .getPath();
        System.out.println(path);
        String content = "";
        String loopContentString ="";
        try {
            is = new FileInputStream(path);
            byte buff[] = new byte[16];
            int len = is.read(buff);
            content = new String(buff, 0, len);
            System.out.println(len);
            while (len != -1) {
                len = is.read(buff);
                System.out.println(len);
                if(len != -1){
                    content += new String(buff,0,len);
                }
            }
            System.out.println(content);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally{
            try {
                is.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
}

结果：其中abc.txt 大小就26个字节
图片描述

读取远程数据接口数据流时，

String queryUrl = "https://www.kuaidi100.com/chaxun?com=yuantong&nu=887240223128139035";

    try {
        URL url = new URL(queryUrl);
        URLConnection con = url.openConnection();
        con.setAllowUserInteraction(false);
        urlStream= url.openStream();
        String type = con.guessContentTypeFromStream(urlStream);
        String charSet = null;
        if (type == null){
            type = con.getContentType();
        }                
        if (type == null || type.trim().length() == 0
                || type.trim().indexOf("text/html") < 0){
            return;
        }
        if (type.indexOf("charset=") > 0){
            charSet = type.substring(type.indexOf("charset=") + 8);
        }
        byte b[] = new byte[100];
        int numRead = urlStream.read(b);
        String content = new String(b, 0, numRead);
        System.out.println("b中的内容用ascii表示,第3个字符的码是="+b[2]+"||第一次:"+numRead+"||"+content);
        int i = 0;
        while (numRead != -1) {
            numRead = urlStream.read(b);
            if (numRead != -1) {
                i++;
                // String newContent = new String(b, 0, numRead);
                String newContent = new String(b, 0, numRead, charSet);
                System.out.println("第"+i+"次:"+numRead+"||"+newContent);
                content += newContent;
            }
        }
        System.out.println(content);
    } catch (MalformedURLException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    }finally{
        try {
            urlStream.close();
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }    }