java 文本框值能输入十五个字母 java中文本框为空怎么设置

//FilterBean.java
public class FilterBean{
public FilterBean(){}
public /*static*/ String filter(String input)/进行HTML过滤
{
if(!hasSpecialChars(input)){
return input;
}
StringBuffer filtered =new StringBuffer(input.length());
char c;
for(int i=0; i<=input.length()-1; i++){
c=input.charAt(i);
switch(c)
{
case '
case '>':filtered.append(">"); break;
//case '"':filtered.append("&uot;"); break;
//case '&':filtered.append("&"); break;
case ' ':filtered.append(" "); break;
case '\n':filtered.append("
"); break;default: filtered.append(c);
}
}
return (filtered.toString());
}
public static boolean hasSpecialChars(String input){
boolean flag=false;
if((input!=null)&&(input.length()>0)){
char c;
for(int i=0; i<=input.length()-1; i++){
c=input.charAt(i);
switch(c)
{
case '>': flag=true; break;
case '
//case '"': flag=true; break;
//case '&': flag=true; break;
case ' ': flag=true; break;
case '\n': flag=true; break;
}
}
}
return flag;
}
public String trans(String chi)//统一字符
{
String result = null;
byte temp [];
try{
temp=chi.getBytes("gb2312");
result = new String(temp);
}
catch(java.io.UnsupportedEncodingException e){
System.out.println (e.toString());
}
return result;
}
public String trans(Object chi)
{
return trans(chi.toString());
}
}
//NullSolve.java
public class NullSolve {  //数据写入数据库之前，将未填写的字段由字符串null改为空("")
public String trim(String s){
if(s==null||s.equalsIgnoreCase("null"))
return null;
else
return s.trim();
}
}