java字符串操作扩充：灵活截取字符串
public class StringUtil {

static int varlen1;
static int varlen2;

static String varstr1;
static String varstr2;
static String varstr3;
public static String indexOf(String sourceStr,String indexStr,int indexNum){
/**

• 原始字符串:sourceStr
• 索引字符串:indexStr
• 固定字符串截取后索引次数的indexNum
• indexOf("ws++rq++sl++dl","++",4)

• 结果:dl
  */
  varlen1 = sourceStr.length();
  varlen2 = indexStr.length();

  int i=0;//字符串下标
  int n=0;//某字符串在指定字符串中的个数
  int m=0;
  int x=0;
  while (i< varlen1){
  varstr1 = sourceStr.substring(i, i);//substr(sourceStr,i,1);
  varstr2 = indexStr.substring(1,1);//获取指定用于截串的字符串的第一个字符

   if(varstr1.equals(varstr2)){
   if(i+varlen2<=varlen1){//判断字符下标
   if(indexStr.equals(sourceStr.substring(i, i+varlen2))){
       n++;
       i=i+varlen2;
       }
   }
   }
   i++;

  }

  x=n;

  if(indexNum <= 0){
  return "";
  }

  if(n==0){
  return sourceStr;
  }

  if(indexNum==1){
  i=0;
  n=0;
  while(ivarstr1 = sourceStr.substring(i, i);
  varstr2 = indexStr.substring(1, 1);
  if(null==varstr3){
  varstr3=sourceStr.substring(i, i);
  }else
  varstr3.concat(sourceStr.substring(i, i));
  if(varstr1.equals(varstr2)){
  if(indexStr.equals(sourceStr.substring(i, i+varlen2))){
  n++;
  if(i==0&&n==1){
  m=varlen2;
  }else{
  return sourceStr.substring(m, i);
  }
  }
  }
  i++;
  }
  }

  if(indexNum<=n+1){
  i=0;
  n=0;
  int c=0;
  while(ivarstr1 = sourceStr.substring(i, i);
  varstr2 = indexStr.substring(1, 1);
  if(varstr1.equals(varstr2)){
  if(indexStr.equals(sourceStr.substring(i, i+varlen2))){
  n++;
  if(n+1==indexNum){
  m=i+varlen2;
  c=n;//存储指字符串出现的次数
  }
  if(n-1==c&&c!=0){
  //当上一个条件满足时，下次出现时返回指定索引的字符串
  return sourceStr.substring(m, i);
  }
  i=i+varlen2;
  }else
  i++;
  }else
  i++;

  }
  }
  //获取截取后的最后一个字符串
  return sourceStr.substring(sourceStr.lastIndexOf(indexStr)+indexStr.length(),sourceStr.length());
  }
  public static void main(String[] args) {
  System.out.println(indexOf("ws++rq++sl++dl","++",3));
  }
  }