记录一个简单的业务逻辑，将base64格式的文件转成本地文件，把文件名做为id，文件绝对路径做为路径存入数据库，当用户传id的时候直接调用数据库下载这个图片，返回结果为byte[]。

这篇是记录工作中一个简单的逻辑：

1.将base64格式的文件转成本地文件，把文件名做为id，文件绝对路径做为路径存入数据库，当用户传id的时候直接调用数据库下载这个图片，返回结果为byte[]。

base64转图片存本地代码：

Base64Util base64Util = new Base64Util();
// 读取配置文件
String path = AlertMessageManger.class.getClassLoader().getResource("config.properties").getPath();//config.properties配置的是文件要保存的路径
FileInputStream in;
in = new FileInputStream(path);
Properties prop = new Properties();
prop.load(in);
// 得到配置文件中的本地路径
String imagePath = prop.getProperty("path");
// 雪花算法生成唯一id
SnowFlakeUtil snowFlake = new SnowFlakeUtil(2, 3);
long randomNumber18 = snowFlake.nextId();// 18位唯一id
map.put("file_id", randomNumber18);
imagePath +="/"+ randomNumber18 + ".jpg";// 本地路径+18位唯一id+后缀                            
base64Util.generateImage(alarm_image_data, imagePath);// base64转文件存到本地
map.put("imagePath", imagePath);
jArray.add(map);
String sql = insertSQL(map);//调用插入数据库的方法把数据插入数据库
executeSql(connection, statement, sql);

图片下载的controller代码：

@SuppressWarnings("static-access")
    @RequestMapping(value = "/download", method = RequestMethod.GET, produces = "application/json;charset=utf8")
    public void fileDownload(@RequestParam(value = "file_id", required = false) String file_id,
            @RequestParam(value = "image_size", required = false) String image_size,
            @RequestParam(value = "image_type", required = false) String image_type, HttpSession session,
            HttpServletResponse response) {
        Object[] sessidRet = getSessionId(session);
        JdbcUtil jdbcUtil = new JdbcUtil();
        String sql = null;
        Connection connection = null;
        Statement statement = null;
        ResultSet resultSet = null;
        String msg = null;
        if (file_id == null || "".equals(file_id)) {
            msg = createResultJson(2, "file_id参数不能为空！");
        }
        if (image_size == null || "".equals(image_size)) {
            msg = createResultJson(2, "image_size参数不能为空！");
        }
        if (!image_size.equals("1") && !image_size.equals("2")) {
            msg = createResultJson(2, "image_size值只能为1或者2");
        }
        if (image_type == null || "".equals(image_type)) {
            msg = createResultJson(2, "image_type参数不能为空！");
        }
        if (!image_type.equals("1") && !image_type.equals("2") && !image_type.equals("3")) {
            msg = createResultJson(2, "image_type值只能为1或者2或者3");
        }
        try {
            OutputStream out;
            if (msg != null) {
                response.reset();
                response.setHeader("Content-type", "text/html;charset=UTF-8");
                out = response.getOutputStream();
                out.write(msg.getBytes("UTF-8"));
                out.close();
                return;
            }
            // DowloadFileContent dfc = fileManageService.downloadFile(file_id, sessid);
            long time1 = System.currentTimeMillis();
            sql = "select 数据库 where file_id=" + file_id;
            logger.info("待执行的SQL：" + sql);
            connection = jdbcUtil.getConnection();
            statement = connection.createStatement();
            resultSet = statement.executeQuery(sql);
            long time2 = 0;
            while (resultSet.next()) {
                String casefile_id = resultSet.getString("file_id");
                byte[] b = null;
                if (casefile_id != null) {
                    b = service.downloadSH(file_id, image_type, image_size);
                    long time_ = System.currentTimeMillis();
                    logger.info("SH下载耗时=" + (time_ - time1));
                }if (b == null) {
                    msg = createResultJson(1, "文件不存在,文件下载失败！");
                    response.setHeader("Content-type", "text/html;charset=UTF-8");
                    out = response.getOutputStream();
                    out.write(msg.getBytes("UTF-8"));
                    out.close();
                    return;
                } else {
                    response.reset();
                    out = response.getOutputStream();
                    out.write(b, 0, b.length);
                    out.close();
                    long time3 = System.currentTimeMillis();
                    logger.info("写流耗时=" + (time3 - time2));
                    return;
                }
            }
        } catch (Exception e) {
            logger.error("文件下载失败", e);
            msg = createResultJson(1, "文件下载失败！");
        } finally {
            try {
                jdbcUtil.CloseConnection(connection, statement, resultSet);
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }

service代码：

@SuppressWarnings("static-access")
    @Override
    public byte[] downloadSH(String fileID, String imagetype, String imagesize) throws Exception {
        if (fileID != null) {
            String sql = null;
            Connection connection = null;
            Statement statement = null;
            ResultSet resultSet = null;
            JdbcUtil jdbcUtil = new JdbcUtil();
            sql = "select imagePath from 数据库 where 1=1 and file_id=" + fileID;
            try {
                connection = jdbcUtil.getConnection();
                statement = connection.createStatement();
                resultSet = statement.executeQuery(sql);// 这里是执行SQL语句查询结果并返回结果集
                String imagePath = null;
                while (resultSet.next()) {
                    imagePath = resultSet.getString("imagePath");
                }
                return InputStream2ByteArray(imagePath);
            } catch (Exception e) {
                e.printStackTrace();
                System.err.println("发生异常情况，导致失败，请重试...........");
            } finally {
                jdbcUtil.CloseConnection(connection, statement, resultSet);
            }
        }
        return null;
    }
　　//读取本地图片转化成byte[]
    public byte[] InputStream2ByteArray(String filePath) throws IOException {
        InputStream in = new FileInputStream(filePath);
        byte[] data = toByteArray(in);
        in.close();
        return data;
    }

    public byte[] toByteArray(InputStream in) throws IOException {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        byte[] buffer = new byte[1024 * 4];
        int n = 0;
        while ((n = in.read(buffer)) != -1) {
            out.write(buffer, 0, n);
        }
        return out.toByteArray();
    }