1.使用 RandomStringUtils 類

String pwd = RandomStringUtils.randomAlphanumeric(8);

這個方法使用起來比較簡單，缺點是不能排除生成的字串裡面會包含 “i，I；l，L；1；o，O” 等易混淆字元。

RandomStringUtils 原始碼在最下面。

2. 下面這個方法可以去掉易混淆字元，但是程式碼量多了點

//隨機生成一個長度為length的字串，本專案中length=8
	 public static String getRandomString(Integer length){
		 length = 8;
	     String str="abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ123456789";
	     Random random=new Random();
	     StringBuffer sb=new StringBuffer();
	     for(int i=0;i<length;i++){
	       int number=random.nextInt(56);
	       sb.append(str.charAt(number));
	     }
	     return sb.toString();
	 }
 

RandomStringUtils 原始碼

/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.commons.lang3;

import java.util.Random;

/**
 * <p>Operations for random {@code String}s.</p>
 * <p>Currently <em>private high surrogate</em> characters are ignored.
 * These are Unicode characters that fall between the values 56192 (db80)
 * and 56319 (dbff) as we don't know how to handle them.
 * High and low surrogates are correctly dealt with - that is if a
 * high surrogate is randomly chosen, 55296 (d800) to 56191 (db7f)
 * then it is followed by a low surrogate. If a low surrogate is chosen,
 * 56320 (dc00) to 57343 (dfff) then it is placed after a randomly
 * chosen high surrogate.</p>
 * <p>RandomStringUtils is intended for simple use cases. For more advanced
 * use cases consider using commons-text
 * <a href="https://commons.apache.org/proper/commons-text/javadocs/api-release/org/apache/commons/text/RandomStringGenerator.html">
 * RandomStringGenerator</a> instead.</p>
 *
 * <p>#ThreadSafe#</p>
 * @since 1.0
 */
public class RandomStringUtils {

    /**
     * <p>Random object used by random method. This has to be not local
     * to the random method so as to not return the same value in the
     * same millisecond.</p>
     */
    private static final Random RANDOM = new Random();

    /**
     * <p>{@code RandomStringUtils} instances should NOT be constructed in
     * standard programming. Instead, the class should be used as
     * {@code RandomStringUtils.random(5);}.</p>
     *
     * <p>This constructor is public to permit tools that require a JavaBean instance
     * to operate.</p>
     */
    public RandomStringUtils() {
      super();
    }

    // Random
    //-----------------------------------------------------------------------
    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of all characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String random(final int count) {
        return random(count, false, false);
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters whose
     * ASCII value is between {@code 32} and {@code 126} (inclusive).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAscii(final int count) {
        return random(count, 32, 127, false, false);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of characters whose
     * ASCII value is between {@code 32} and {@code 126} (inclusive).</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomAscii(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomAscii(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of Latin alphabetic
     * characters (a-z, A-Z).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAlphabetic(final int count) {
        return random(count, true, false);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of Latin alphabetic characters (a-z, A-Z).</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomAlphabetic(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomAlphabetic(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of Latin alphabetic
     * characters (a-z, A-Z) and the digits 0-9.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomAlphanumeric(final int count) {
        return random(count, true, true);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of Latin alphabetic
     * characters (a-z, A-Z) and the digits 0-9.</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomAlphanumeric(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomAlphanumeric(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters specified.</p>
     *
     * <p>Characters will be chosen from the set of characters which match the POSIX [:graph:]
     * regular expression character class. This class contains all visible ASCII characters
     * (i.e. anything except spaces and control characters).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     * @since 3.5
     */
    public static String randomGraph(final int count) {
        return random(count, 33, 126, false, false);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of \p{Graph} characters.</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomGraph(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomGraph(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of numeric
     * characters.</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     */
    public static String randomNumeric(final int count) {
        return random(count, false, true);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of \p{Digit} characters.</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomNumeric(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomNumeric(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters specified.</p>
     *
     * <p>Characters will be chosen from the set of characters which match the POSIX [:print:]
     * regular expression character class. This class includes all visible ASCII characters and spaces
     * (i.e. anything except control characters).</p>
     *
     * @param count  the length of random string to create
     * @return the random string
     * @since 3.5
     */
    public static String randomPrint(final int count) {
        return random(count, 32, 126, false, false);
    }

    /**
     * <p>Creates a random string whose length is between the inclusive minimum and
     * the exclusive maximum.</p>
     *
     * <p>Characters will be chosen from the set of \p{Print} characters.</p>
     *
     * @param minLengthInclusive the inclusive minimum length of the string to generate
     * @param maxLengthExclusive the exclusive maximum length of the string to generate
     * @return the random string
     * @since 3.5
     */
    public static String randomPrint(final int minLengthInclusive, final int maxLengthExclusive) {
        return randomPrint(RandomUtils.nextInt(minLengthInclusive, maxLengthExclusive));
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alpha-numeric
     * characters as indicated by the arguments.</p>
     *
     * @param count  the length of random string to create
     * @param letters  if {@code true}, generated string may include
     *  alphabetic characters
     * @param numbers  if {@code true}, generated string may include
     *  numeric characters
     * @return the random string
     */
    public static String random(final int count, final boolean letters, final boolean numbers) {
        return random(count, 0, 0, letters, numbers);
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of alpha-numeric
     * characters as indicated by the arguments.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at
     * @param end  the position in set of chars to end before
     * @param letters  if {@code true}, generated string may include
     *  alphabetic characters
     * @param numbers  if {@code true}, generated string may include
     *  numeric characters
     * @return the random string
     */
    public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers) {
        return random(count, start, end, letters, numbers, null, RANDOM);
    }

    /**
     * <p>Creates a random string based on a variety of options, using
     * default source of randomness.</p>
     *
     * <p>This method has exactly the same semantics as
     * {@link #random(int,int,int,boolean,boolean,char[],Random)}, but
     * instead of using an externally supplied source of randomness, it uses
     * the internal static {@link Random} instance.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at
     * @param end  the position in set of chars to end before
     * @param letters  only allow letters?
     * @param numbers  only allow numbers?
     * @param chars  the set of chars to choose randoms from.
     *  If {@code null}, then it will use the set of all chars.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not
     *  {@code (end - start) + 1} characters in the set array.
     */
    public static String random(final int count, final int start, final int end, final boolean letters, final boolean numbers, final char... chars) {
        return random(count, start, end, letters, numbers, chars, RANDOM);
    }

    /**
     * <p>Creates a random string based on a variety of options, using
     * supplied source of randomness.</p>
     *
     * <p>If start and end are both {@code 0}, start and end are set
     * to {@code ' '} and {@code 'z'}, the ASCII printable
     * characters, will be used, unless letters and numbers are both
     * {@code false}, in which case, start and end are set to
     * {@code 0} and {@link Character#MAX_CODE_POINT}.
     *
     * <p>If set is not {@code null}, characters between start and
     * end are chosen.</p>
     *
     * <p>This method accepts a user-supplied {@link Random}
     * instance to use as a source of randomness. By seeding a single
     * {@link Random} instance with a fixed seed and using it for each call,
     * the same random sequence of strings can be generated repeatedly
     * and predictably.</p>
     *
     * @param count  the length of random string to create
     * @param start  the position in set of chars to start at (inclusive)
     * @param end  the position in set of chars to end before (exclusive)
     * @param letters  only allow letters?
     * @param numbers  only allow numbers?
     * @param chars  the set of chars to choose randoms from, must not be empty.
     *  If {@code null}, then it will use the set of all chars.
     * @param random  a source of randomness.
     * @return the random string
     * @throws ArrayIndexOutOfBoundsException if there are not
     *  {@code (end - start) + 1} characters in the set array.
     * @throws IllegalArgumentException if {@code count} &lt; 0 or the provided chars array is empty.
     * @since 2.0
     */
    public static String random(int count, int start, int end, final boolean letters, final boolean numbers,
                                final char[] chars, final Random random) {
        if (count == 0) {
            return StringUtils.EMPTY;
        } else if (count < 0) {
            throw new IllegalArgumentException("Requested random string length " + count + " is less than 0.");
        }
        if (chars != null && chars.length == 0) {
            throw new IllegalArgumentException("The chars array must not be empty");
        }

        if (start == 0 && end == 0) {
            if (chars != null) {
                end = chars.length;
            } else {
                if (!letters && !numbers) {
                    end = Character.MAX_CODE_POINT;
                } else {
                    end = 'z' + 1;
                    start = ' ';
                }
            }
        } else {
            if (end <= start) {
                throw new IllegalArgumentException("Parameter end (" + end + ") must be greater than start (" + start + ")");
            }
        }

        final int zero_digit_ascii = 48;
        final int first_letter_ascii = 65;

        if (chars == null && (numbers && end <= zero_digit_ascii
                || letters && end <= first_letter_ascii)) {
            throw new IllegalArgumentException("Parameter end (" + end + ") must be greater then (" + zero_digit_ascii + ") for generating digits " +
                    "or greater then (" + first_letter_ascii + ") for generating letters.");
        }

        final StringBuilder builder = new StringBuilder(count);
        final int gap = end - start;

        while (count-- != 0) {
            int codePoint;
            if (chars == null) {
                codePoint = random.nextInt(gap) + start;

                switch (Character.getType(codePoint)) {
                case Character.UNASSIGNED:
                case Character.PRIVATE_USE:
                case Character.SURROGATE:
                    count++;
                    continue;
                }

            } else {
                codePoint = chars[random.nextInt(gap) + start];
            }

            final int numberOfChars = Character.charCount(codePoint);
            if (count == 0 && numberOfChars > 1) {
                count++;
                continue;
            }

            if (letters && Character.isLetter(codePoint)
                    || numbers && Character.isDigit(codePoint)
                    || !letters && !numbers) {
                builder.appendCodePoint(codePoint);

                if (numberOfChars == 2) {
                    count--;
                }

            } else {
                count++;
            }
        }
        return builder.toString();
    }


    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters
     * specified by the string, must not be empty.
     * If null, the set of all characters is used.</p>
     *
     * @param count  the length of random string to create
     * @param chars  the String containing the set of characters to use,
     *  may be null, but must not be empty
     * @return the random string
     * @throws IllegalArgumentException if {@code count} &lt; 0 or the string is empty.
     */
    public static String random(final int count, final String chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, chars.toCharArray());
    }

    /**
     * <p>Creates a random string whose length is the number of characters
     * specified.</p>
     *
     * <p>Characters will be chosen from the set of characters specified.</p>
     *
     * @param count  the length of random string to create
     * @param chars  the character array containing the set of characters to use,
     *  may be null
     * @return the random string
     * @throws IllegalArgumentException if {@code count} &lt; 0.
     */
    public static String random(final int count, final char... chars) {
        if (chars == null) {
            return random(count, 0, 0, false, false, null, RANDOM);
        }
        return random(count, 0, chars.length, false, false, chars, RANDOM);
    }

}