用Java从MySQL读取blob [英] Reading a blob from MySQL with Java

问题描述

我在使用Java从MySQL数据库中读取blob时遇到问题。
我需要用jax-rs编写一个web服务来提供保存在数据库中的图像。对于传输，必须使用Base64进行编码。

I have a problem reading a blob from a MySQL database with Java. I need to write a webservice with jax-rs to deliver an image saved in the database. For transport, it has to be encoded using Base64.

这是我的代码：

public String getImage(@PathParam("id") int id) throws SQLException{
    System.out.println(id);
    String img64str = "null";
    Blob image = null;
    Connection conn = MySQLConnection.getInstance();
    if(conn != null)
    {
        try{
        // Anfrage-Statement erzeugen.
        Statement query;
        query = conn.createStatement();

        // Ergebnistabelle erzeugen und abholen.

            String sql = "SELECT bild FROM beitraege where id="+id;
            ResultSet result = query.executeQuery(sql);
            //Ergebniss zur�ckliefern
            while (result.next()) {
                System.out.println("while");
                image = result.getBlob("bild");
                InputStream binaryStream = image.getBinaryStream(1, image.length());
                String str= binaryStream.toString();
                byte[] bdata=str.getBytes();
                byte[] img64 = Base64.encode(bdata);
                img64str = new String(img64);
            }

        }catch (SQLException e) {
            e.printStackTrace();
        }
   }

    return img64str;
}

不知何故，它只返回这样的东西（显示结果列表已解码）：

Somehow, it only returns something like this (shown result list decoded):

java.io.ByteArrayInputStream@cc90a0a

推荐答案

问题在于toString（）调用： binaryStream.toString（）; BinaryInputStream不实现 toString（）。
使用类似的东西来读取字节：

The problem lies in the "toString()" call: binaryStream.toString(); BinaryInputStream do not implement toString(). Use something like this to read the bytes:

int ch;

//read bytes from ByteArrayInputStream using read method
while((ch = binaryStream.read()) != -1)
{
   System.out.print((char)ch);
   // store it to an array...
}

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