java 空格替换%20

public String replaceSpace(StringBuffer str2) {
    
    StringBuffer str4 = new StringBuffer();
    
    
    int length=str2.length();
    char []str3=str2.toString().toCharArray();
    
    for(int i=0;i<length;i++)
    {
        if(str3[i]!=' ')
        {
            str4.append(str3[i]);
        }
        else{
            
            str4.append("%");
            str4.append("2");
            str4.append("0");
            
        }
    }
    //str4.append("\0");
    return str4.toString();
    
}