java获取字符串指定位置的字符_查找子字符串在字符串中的位置

有时会遇到从一个大的字符串提取一个子字符串的情况。

 

public static void main(String[] args) {
        Test t = new Test();
        String str ="xmlns:etc=\"http://www.wps.cn/officeDocument/2017/etCustomData\"><sheetPr codeName=\"Sheet7\"><tabColor theme=\"5\" tint=\"0.599993896298105\"/><pageSetUpPr fitToPage=\"1\"/></sheetPr><dimension ref=\"A1:J29\"/><sheetViews><sheetView showGridLines=\"0\" zoomScale=\"110\" zoomScaleNormal=\"110\"";
        String startStr ="dimension ref=\"A1:";
        String endStr ="\"/><sheetViews>";
        int start = t.getKMPIndex(str, startStr);
        int end = t.getKMPIndex(str, endStr);

        String sub = str.substring(start+15, end);
        System.out.println(sub);
    }
    
    public int getKMPIndex(String string,String substring){
        int i = 0;        
        int j = 0;        
        int[] nextval = getNextVal(substring);        
        char[] stringCharArray = string.toCharArray();        
        char[] substringCahrArray = substring.toCharArray();        
        int stringlength = string.length() ;        
        int substringlength =    substring.length();        
        while (i < stringlength && j < substringlength){
            if(j == -1 || stringCharArray[i] == substringCahrArray[j]){
                i++;                
                j++;            
            }else { 
                j = nextval[j];
            }       
        }        
        if( j >= substringlength){            
            return i - substringlength;        
        }else {            
            return -1; 
        }
    }
    private int[] getNextVal(String str){
        int length = str.length();        
        int[] nextval = new int[length];        
        char[] strchar = str.toCharArray();        
        int j= 0;        
        int k = -1;        
        nextval[0] = -1;        
        while (j < length-1){
            if(k== -1 || strchar[j] == strchar[k] ){
                j++;                
                k++;                
                if(strchar[j] != strchar[k]){
                    nextval[j] = k;                
                }else {
                    nextval[j] = nextval[k];
                }            
            }else {                
                k = nextval[k];            
            }        
        }
        return nextval;    
    }