Tomcat中的URLEncoder，使用十六进制来编码

最新推荐文章于 2023-10-13 17:45:18 发布

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#tomcat #exception #byte #string #encoding #buffer

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本文详细介绍了Java中URLEncoder类的实现原理与使用方法，包括十六进制基本字符集、安全字符集构建以及字符串编码流程。通过实例演示了如何自定义URL编码规则，对于理解Java网络编程和安全编码具有重要意义。

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package org.apache.catalina.util;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.util.BitSet;

public class URLEncoder {
//十六进制基本字符
 protected static final char[] hexadecimal =
    {'0', '1', '2', '3', '4', '5', '6', '7', '8', '9',
     'A', 'B', 'C', 'D', 'E', 'F'};

    //Array containing the safe characters set. 
   //BitSet 实现了一个按需增长的位向量
    protected BitSet safeCharacters = new BitSet(256);

    public URLEncoder() {
        for (char i = 'a'; i <= 'z'; i++) {
            addSafeCharacter(i);
        }
        for (char i = 'A'; i <= 'Z'; i++) {
            addSafeCharacter(i);
        }
        for (char i = '0'; i <= '9'; i++) {
            addSafeCharacter(i);
        }
    }

    public void addSafeCharacter( char c ) {
        safeCharacters.set( c );
    }

    public String encode( String path ) {
        int maxBytesPerChar = 10;
        StringBuilder rewrittenPath = new StringBuilder(path.length());
        //使用OutputStreamReader组装ByteArrayOutputStream将字符写入到二进制数组中
        ByteArrayOutputStream buf = new ByteArrayOutputStream(maxBytesPerChar);
        OutputStreamWriter writer = null;
        try {
            writer = new OutputStreamWriter(buf, "UTF8");
        } catch (Exception e) {
            e.printStackTrace();
            writer = new OutputStreamWriter(buf);
        }

        for (int i = 0; i < path.length(); i++) {
            int c = path.charAt(i);
            if (safeCharacters.get(c)) {
                rewrittenPath.append((char)c);
            } else {
                // convert to external encoding before hex conversion
                try {
                    writer.write((char)c);
                    writer.flush();
                } catch(IOException e) {
                    buf.reset();
                    continue;
                }
                byte[] ba = buf.toByteArray();
                for (int j = 0; j < ba.length; j++) {
                    // Converting each byte in the buffer
                    byte toEncode = ba[j];
                    rewrittenPath.append('%');
                   //编码规则
                    int low = toEncode & 0x0f;
                    int high = (toEncode & 0xf0) >> 4;
                    rewrittenPath.append(hexadecimal[high]);
                    rewrittenPath.append(hexadecimal[low]);
                }
                buf.reset();
            }
        }
        return rewrittenPath.toString();
    }
}