URLDecoder对参数进行解码时候，代码如：

URLDecoder.decode(param,"utf-8");

有时候会出现类似如下的错误：

URLDecoder异常Illegal hex characters in escape (%)

这是因为传参有一些特殊字符，比如%号或者说+号，导致不能解析，报错

解决方法是：

public static String replacer(StringBuffer outBuffer) {

String data = outBuffer.toString();

try {

data = data.replaceAll("%(?![0-9a-fA-F]{2})", "%25");

data = data.replaceAll("\\+", "%2B");

data = URLDecoder.decode(data, "utf-8");

} catch (Exception e) {

e.printStackTrace();

}

return data;

}

URLDecoder源码：

public static String decode(String s, String enc)

throws UnsupportedEncodingException{

boolean needToChange = false;

int numChars = s.length();

StringBuffer sb = new StringBuffer(numChars > 500 ? numChars / 2 : numChars);

int i = 0;

if (enc.length() == 0) {

throw new UnsupportedEncodingException ("URLDecoder: empty string enc parameter");

}

char c;

byte[] bytes = null;

while (i < numChars) {

c = s.charAt(i);

switch (c) {

case '+':

sb.append(' ');

i++;

needToChange = true;

break;

case '%':

/*

* Starting with this instance of %, process all

* consecutive substrings of the form %xy. Each

* substring %xy will yield a byte. Convert all

* consecutive bytes obtained this way to whatever

* character(s) they represent in the provided

* encoding.

*/

try {

// (numChars-i)/3 is an upper bound for the number

// of remaining bytes

if (bytes == null)

bytes = new byte[(numChars-i)/3];

int pos = 0;

while ( ((i+2) < numChars) &&

(c=='%')) {

int v = Integer.parseInt(s.substring(i+1,i+3),16);

if (v < 0)

throw new IllegalArgumentException("URLDecoder: Illegal hex characters in escape (%) pattern - negative value");

bytes[pos++] = (byte) v;

i+= 3;

if (i < numChars)

c = s.charAt(i);

}

// A trailing, incomplete byte encoding such as

// "%x" will cause an exception to be thrown

if ((i < numChars) && (c=='%'))

throw new IllegalArgumentException(

"URLDecoder: Incomplete trailing escape (%) pattern");

sb.append(new String(bytes, 0, pos, enc));

} catch (NumberFormatException e) {

throw new IllegalArgumentException(

"URLDecoder: Illegal hex characters in escape (%) pattern - "

+ e.getMessage());

}

needToChange = true;

break;

default:

sb.append(c);

i++;

break;

}

}

return (needToChange? sb.toString() : s);

}