开发总结的一些小工具api

 public static String genRandomStr(int length){
        //35是因为数组是从0开始的，26个字母+10个数字
        final int  maxNum = 36;
        int i;  //生成的随机数
        int count = 0; //生成的密码的长度
        char[] str = { ‘a‘, ‘b‘, ‘c‘, ‘d‘, ‘e‘, ‘f‘, ‘g‘, ‘h‘, ‘i‘, ‘j‘, ‘k‘,
                ‘l‘, ‘m‘, ‘n‘, ‘o‘, ‘p‘, ‘q‘, ‘r‘, ‘s‘, ‘t‘, ‘u‘, ‘v‘, ‘w‘,
                ‘x‘, ‘y‘, ‘z‘, ‘0‘, ‘1‘, ‘2‘, ‘3‘, ‘4‘, ‘5‘, ‘6‘, ‘7‘, ‘8‘, ‘9‘ };

        StringBuffer pwd = new StringBuffer("");
        Random r = new Random();
        while(count < length){
            //生成随机数，取绝对值，防止生成负数，

            i = Math.abs(r.nextInt(maxNum));  //生成的数最大为36-1

            if (i >= 0 && i < str.length) {
                pwd.append(str[i]);
                count ++;
            }
        }
        return pwd.toString();
    }

public static String random(int n) {
        if (n < 1 || n > 10) {
            throw new IllegalArgumentException("cannot random " + n + " bit number");
        }
        Random ran = new Random();
        if (n == 1) {
            return String.valueOf(ran.nextInt(10));
        }
        int bitField = 0;
        char[] chs = new char[n];
        for (int i = 0; i < n; i++) {
            while(true) {
                int k = ran.nextInt(10);
                if( (bitField & (1 << k)) == 0) {
                    bitField |= 1 << k;
                    chs[i] = (char)(k + ‘0‘);
                    break;
                }
            }
        }
        return new String(chs);
    }

public static String string2MD5(String inStr){
        MessageDigest md5 = null;
        try{
            md5 = MessageDigest.getInstance("MD5");
        }catch (Exception e){
            return "";
        }
        char[] charArray = inStr.toCharArray();
        byte[] byteArray = new byte[charArray.length];

        for (int i = 0; i < charArray.length; i++)
            byteArray[i] = (byte) charArray[i];
        byte[] md5Bytes = md5.digest(byteArray);
        StringBuffer hexValue = new StringBuffer();
        for (int i = 0; i < md5Bytes.length; i++){
            int val = ((int) md5Bytes[i]) & 0xff;
            if (val < 16)
                hexValue.append("0");
            hexValue.append(Integer.toHexString(val));
        }
        return hexValue.toString();

    }

/**
     * 二进制流转BASE64字符串
     * @param data
     * @return
     */
    public static String byteToBase(byte[] data){
        BASE64Encoder encoder = new BASE64Encoder();
        return data != null ? encoder.encode(data) : "";
    }

    /**
     * BASE64字符串转二进制流
     * @param str
     * @return
     * @throws Exception
     */
    public static byte[] baseTobyte(String str) throws Exception{
        BASE64Decoder decoder = new BASE64Decoder();
        return str != null ? decoder.decodeBuffer(str) : null;
    }

/**
     * 文件流转BASE64字符串
     * @param in
     * @return
     */
    public static String fileToBase(InputStream in) {
        // 将图片文件转化为字节数组字符串，并对其进行Base64编码处理
        byte[] data = null;
        // 读取图片字节数组
        try {
            ByteArrayOutputStream swapStream = new ByteArrayOutputStream();
            byte[] buff = new byte[100];
            int rc = 0;
            while ((rc = in.read(buff, 0, 100)) > 0) {
                swapStream.write(buff, 0, rc);
            }
            data = swapStream.toByteArray();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
        return new String(Base64.encodeBase64(data));
    }

import org.springframework.web.multipart.MultipartFile;

import java.io.*;

public class BaseToMultipartFile implements MultipartFile {
    private final byte[] imgContent;
    private final String header;

    public BaseToMultipartFile(byte[] imgContent, String header) {
        this.imgContent = imgContent;
        this.header = header.split(";")[0];
    }

    @Override
    public String getName() {
        return System.currentTimeMillis() + Math.random() + "." + header.split("/")[1];
    }

    @Override
    public String getOriginalFilename() {
        return System.currentTimeMillis() + (int)Math.random() * 10000 + "." + header.split("/")[1];
    }

    @Override
    public String getContentType() {
        return header.split(":")[1];
    }

    @Override
    public boolean isEmpty() {
        return imgContent == null || imgContent.length == 0;
    }

    @Override
    public long getSize() {
        return imgContent.length;
    }

    @Override
    public byte[] getBytes() throws IOException {
        return imgContent;
    }

    @Override
    public InputStream getInputStream() throws IOException {
        return new ByteArrayInputStream(imgContent);
    }

    @Override
    public void transferTo(File dest) throws IOException, IllegalStateException {
        new FileOutputStream(dest).write(imgContent);
    }

}

/**
     * BASE64转MultipartFile
     * @param base64
     * @return
     */
    public static MultipartFile base64ToMultipart(String base64) throws Exception{
            String[] baseStrs = base64.split(",");
            BASE64Decoder decoder = new BASE64Decoder();
            byte[] b = new byte[0];
            b = decoder.decodeBuffer(baseStrs[1]);
            for(int i = 0; i < b.length; ++i) {
                if (b[i] < 0) {
                    b[i] += 256;
                }
            }
            return new BaseToMultipartFile(b, baseStrs[0]);
    }