Java同样的汉字在服务器和本地的电脑上URLencode 出来的结果不一致

在CSDN问答中看到这个问题，通常这类问题都是由于字符串的编码导致的。

代码如下：

         String oldStr = new String("中文字符");  //我的环境默认UTF-8
        System.out.println(URLEncoder.encode(oldStr));
        try {
            String newStr = new String(oldStr.getBytes(), "gb2312");
            System.out.println(URLEncoder.encode(newStr));
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }  

输出：
%E4%B8%AD%E6%96%87%E5%AD%97%E7%AC%A6
%E6%B6%93%EF%BF%BD%EF%BF%BD%EF%BF%BD%E7%80%9B%EF%BF%BD%E7%BB%97%EF%BF%BD

UTF-8的才是正确的。

URLEncoder.encode(String s) 过时了，使用下面的方法：

        String oldStr = new String("中文字符");
        try {
            System.out.println(URLEncoder.encode(oldStr, "utf-8"));
            System.out.println(URLEncoder.encode(oldStr, "gb2312"));
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

输出：

%E4%B8%AD%E6%96%87%E5%AD%97%E7%AC%A6
%D6%D0%CE%C4%D7%D6%B7%FB

查看默认编码：

System.out.println(Charset.defaultCharset()); //查看默认编码

问题又来了，两次输出的 GB2312 编码的不一样！一次那么长，一次却很短！

查看的实现源码吧！

package java.net;

import java.io.CharArrayWriter;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.IllegalCharsetNameException;
import java.nio.charset.UnsupportedCharsetException;
import java.security.AccessController;
import java.util.BitSet;
import sun.security.action.GetPropertyAction;

public class URLEncoder
{
  static BitSet dontNeedEncoding;
  static final int caseDiff = 32;
  static String dfltEncName = null;

  @Deprecated
  public static String encode(String paramString)
  {
    String str = null;
    try
    {
      str = encode(paramString, dfltEncName);
    }
    catch (UnsupportedEncodingException localUnsupportedEncodingException)
    {
    }
    return str;
  }

  public static String encode(String paramString1, String paramString2)
    throws UnsupportedEncodingException
  {
    int i = 0;
    StringBuffer localStringBuffer = new StringBuffer(paramString1.length());
    CharArrayWriter localCharArrayWriter = new CharArrayWriter();
    if (paramString2 == null)
      throw new NullPointerException("charsetName");
    Charset localCharset;
    try
    {
      localCharset = Charset.forName(paramString2);
    }
    catch (IllegalCharsetNameException localIllegalCharsetNameException)
    {
      throw new UnsupportedEncodingException(paramString2);
    }
    catch (UnsupportedCharsetException localUnsupportedCharsetException)
    {
      throw new UnsupportedEncodingException(paramString2);
    }
    int j = 0;
    while (j < paramString1.length())
    {
      int k = paramString1.charAt(j);
      if (dontNeedEncoding.get(k))
      {
        if (k == 32)
        {
          k = 43;
          i = 1;
        }
        localStringBuffer.append((char)k);
        ++j;
      }
      else
      {
        do
        {
          localCharArrayWriter.write(k);
          if ((k < 55296) || (k > 56319) || (j + 1 >= paramString1.length()))
            continue;
          int l = paramString1.charAt(j + 1);
          if ((l < 56320) || (l > 57343))
            continue;
          localCharArrayWriter.write(l);
          ++j;
        }
        while ((++j < paramString1.length()) && (!dontNeedEncoding.get(k = paramString1.charAt(j))));
        localCharArrayWriter.flush();
        String str = new String(localCharArrayWriter.toCharArray());
        byte[] arrayOfByte = str.getBytes(localCharset);
        for (int i1 = 0; i1 < arrayOfByte.length; ++i1)
        {
          localStringBuffer.append('%');
          char c = Character.forDigit(arrayOfByte[i1] >> 4 & 0xF, 16);
          if (Character.isLetter(c))
            c = (char)(c - ' ');
          localStringBuffer.append(c);
          c = Character.forDigit(arrayOfByte[i1] & 0xF, 16);
          if (Character.isLetter(c))
            c = (char)(c - ' ');
          localStringBuffer.append(c);
        }
        localCharArrayWriter.reset();
        i = 1;
      }
    }
    return (i != 0) ? localStringBuffer.toString() : paramString1;
  }

  static
  {
    dontNeedEncoding = new BitSet(256);
    for (int i = 97; i <= 122; ++i)
      dontNeedEncoding.set(i);
    for (i = 65; i <= 90; ++i)
      dontNeedEncoding.set(i);
    for (i = 48; i <= 57; ++i)
      dontNeedEncoding.set(i);
    dontNeedEncoding.set(32);
    dontNeedEncoding.set(45);
    dontNeedEncoding.set(95);
    dontNeedEncoding.set(46);
    dontNeedEncoding.set(42);
    dfltEncName = (String)AccessController.doPrivileged(new GetPropertyAction("file.encoding"));
  }
}

通过查看源码我们可以明白，传入的第二个参数是输出的编码，而不是指将传入的第一个参数转换为什么类型的编码；

默认它应该是读取的容器（如：Tomcat）的默认编码；

我们可以通过执行以下代码查看：

	    dfltEncName = (String)AccessController.doPrivileged(new GetPropertyAction("file.encoding"));
	    
	    System.out.println(dfltEncName);

需要在项目中添加一个类：GetPropertyAction.java

package sun.security.action;

import java.security.PrivilegedAction;

public class GetPropertyAction
  implements PrivilegedAction<String>
{
  private String theProp;
  private String defaultVal;

  public GetPropertyAction(String paramString)
  {
    this.theProp = paramString;
  }

  public GetPropertyAction(String paramString1, String paramString2)
  {
    this.theProp = paramString1;
    this.defaultVal = paramString2;
  }

  public String run()
  {
    String str = System.getProperty(this.theProp);
    return (str == null) ? this.defaultVal : str;
  }
}

所以正确的姿势是先判断你的默认编码是不是“UTF-8”,使用：Charset.defaultCharset()；

如果不是，就将其转换为“UTF-8”，使用：String newStr = new String(oldStr.getBytes(), "utf-8");

然后再编码：URLEncoder.encode(newStr, "utf-8");

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