Simple implementation of Java upload image file function

Generally speaking, there are two ways to upload pictures. One is to write picture files to the database, and the other is to save them to the server file directory. The picture files written to the database need to be converted into binary stream format, which takes up more database space and is suitable for the storage of a small number of pictures. For example, the advantage of writing some small icons in the system to the database is that they are relatively safe and not easy to be accidentally deleted by users.

If a large number of pictures are stored, the usual practice is to save them to a folder on the server. There are many ways to upload. You can use streaming or FTP. Here, you can use fileUpload.

With the different system scale, the processing methods of image files are also different. If the number of pictures in the system is not very large, all pictures can be directly stored in the same directory. If the pictures accumulate more, the pictures can be classified and stored according to the material classification, which will save some time to find files in the disk.

When uploading pictures to files, you can directly upload pictures to the directory, write the picture file name and file path to the database, or dynamically create file paths in the program. If the company requires pictures to be stored on a special server, it is more appropriate to write the file path alive at this time. Generally, if a material (material) corresponds to a picture, it is easier to handle. If it corresponds to multiple pictures, it needs to be recycled. On the one hand, it is necessary to deal with the dynamic display of pictures. On the other hand, it is necessary to check whether the names of picture files are repeated. In addition, you need to cooperate with the transaction when processing pictures (uploading, deleting and modifying).

The following focuses on the most basic implementation of image upload using file upload.

1. Use the file label on the front end:

2. Set the enctype format of the file: multipart / form data

Description of enctype = "multipart / form data":

If this format is used in JSP, the corresponding servlet cannot use request Getparameter() to obtain parameters, first parse the data in the request object using the parserequest method of the servletfileupload object, and then use the isformfield flag of the parsed element in conjunction with the getfieldname method to obtain data.

3. Implementation of fileuploadservlet:

This class inherits abstractitemservlet: the abstract parent class of all material servlets, which is responsible for instantiating itemmanager

Itemmanagerimpl is a subclass that implements the itemmanager interface. There is a problem with this design mode, including salary optimization, but here, in order to illustrate the image upload, we don't do more irrelevant details.

Summary:

About init () initialization method: when the servlet is initialized, the directory is created dynamically. Here, an upload and temporary file temppath are created into the following directory of the project under Tomcat's webapps. It is worth noting that the call to super needs to be displayed here Init() method (super is not a reference to the parent object, but is responsible for calling the method of the parent class). Otherwise, it may cause null pointers to this class. Uploading is roughly divided into three steps: parsing the form using the fileUpload component; parsing the data passed from the form and returning the list collection data - type: fileitem; finally uploading the picture. Use isformfield() of fileitem Method to determine whether it is an ordinary text or a file; Use fileitem Write (new file (uploadpath, filename)) uploads a file. The first parameter is: full path (excluding file name), and the second parameter is: file name;

Processing plain text data:

Uploading is a mature technology for many years. Many of them have been encapsulated. We can use them directly in our usual projects, but it is essential to understand some basic principles.

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