String str = "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStT
       uUvVwWxXyYzZ0123456789";

Random random = new Random();
int index = random.nextInt(str.length());

char c = str.charAt(index);

StringBuffer stringBuffer = new StringBuffer();
//确定字符串长度
int stringLength = (int) (Math.random()*10);

for (int j = 0; j < stringLength; j++) {
  int index = random.nextInt(str.length());
  char c = str.charAt(index);
  stringBuffer.append(c);  
 }
//将StringBuffer转换为String类型的字符串
String string = stringBuffer.toString();

List<String> listString = new ArrayList<String>();

//判断当前的list容器中是否已有刚生成的字符串，满足每条字符串不可重复性
if(!(listString.contains(stringBuffer.toString()))){
   listString.add(stringBuffer.toString());
 }else {
   //i-- 如果不满足则重新生成
  i--;
 }

import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.List;
import java.util.Random;

public class RandomString {

  public static void main(String[] args) {
    List<String> strList = randomString();
    System.out.println("------随机生成的10条字符串-------");
    for (String string : strList) {
      System.out.println(string);
    }
    System.out.println("------------排序后------------");
    Collections.sort(strList);
    for (String string : strList) {
      System.out.println(string);
    }  
  }
  public static List<String> randomString(){
    //将所有的大小写字母和0-9数字存入字符串中
    String str = "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ0123456789";
    Random random = new Random();
    List<String> listString = new ArrayList<String>();
    String strArray[ ] = new String[10];
    //生成10条长度为1-10的随机字符串
    for (int i = 0; i < 10; i++) {
      StringBuffer stringBuffer = new StringBuffer();
      //确定字符串长度
      int stringLength = (int) (Math.random()*10);
       for (int j = 0; j < stringLength; j++) {
         //先随机生成初始定义的字符串 str 的某个索引，以获取相应的字符
        int index = random.nextInt(str.length());
        char c = str.charAt(index);
        stringBuffer.append(c);  
       }
       //判断当前的list容器中是否已有刚生成的字符串，满足每条字符串不可重复性
       if (!(listString.contains(stringBuffer.toString()))) {
         listString.add(stringBuffer.toString());
      }else {
        i--;
      }

    }
    return listString;
  }
}