好设计，迁移不费劲

前言

尽管java的口号：Write Once, Run Anywhere ，但现实非常残酷。不同的操作系统、不同的容器总是让我们：Write Once，Debug Anywhere。所以关键还是要看设计。好的设计能降低迁移成本。

近期须要将roller迁移到百度云中，发现roller设计的真不错。很easy就看迁移到云中了。

迁移的主要是数据，roller使用mysql，而百度云也提高mysql。这个基本不须要考虑迁移。主要是roller的图片上传功能：

1、怎样将已经上传的图片迁移到百度的bcs中？

2、怎样以最小的代价让将上传图片的功能迁移到百度bcs中？

添加一个切换开关：roller.properties

baiduyun.accessKey=dtjTg3L9xm
baiduyun.secretKey=9V1L9mul9IVb
baiduyun.bucket=hello
enabled.use.baiduyun=true

扩展存储文件的实现类

package org.apache.roller.weblogger.business;

import java.io.InputStream;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.roller.weblogger.config.WebloggerConfig;
import org.apache.roller.weblogger.pojos.FileContent;
import org.apache.roller.weblogger.pojos.MediaFile;
import org.apache.roller.weblogger.pojos.Weblog;
import org.apache.roller.weblogger.util.RollerMessages;

import com.baidu.inf.iis.bcs.BaiduBCS;
import com.baidu.inf.iis.bcs.auth.BCSCredentials;
import com.baidu.inf.iis.bcs.model.Empty;
import com.baidu.inf.iis.bcs.model.ObjectMetadata;
import com.baidu.inf.iis.bcs.model.X_BS_ACL;
import com.baidu.inf.iis.bcs.request.PutObjectRequest;


/**
 * Manages contents of the file uploaded to Roller weblogs.  
 * 
 * This base implementation writes file content to a file system.
 */
public class BaiduYunFileContentManagerImpl extends FileContentManagerImpl {

    private static Log log = LogFactory.getLog(BaiduYunFileContentManagerImpl.class);

    private String host = "bcs.duapp.com";
    private String accessKey = "";
    private String secretKey = "";
    private String bucket = "";
    private BaiduBCS baiduBCS = null;

    /**
     * Create file content manager.
     */
    public BaiduYunFileContentManagerImpl() {

        accessKey = WebloggerConfig.getProperty("baiduyun.accessKey");
        secretKey = WebloggerConfig.getProperty("baiduyun.secretKey");
        bucket = WebloggerConfig.getProperty("baiduyun.bucket");

        BCSCredentials credentials = new BCSCredentials(accessKey, secretKey);
        baiduBCS = new BaiduBCS(credentials, host);
        baiduBCS.setDefaultEncoding("UTF-8"); // Default UTF-8


    }


    /**
     * @see org.apache.roller.weblogger.model.FileContentManager#getFileContent(weblog, java.lang.String)
     */
    public FileContent getFileContent(Weblog weblog, String fileId) 
            throws FileNotFoundException, FilePathException {

        log.info("=====================get file content:" + fileId);
        final InputStream is = baiduBCS.getObject(bucket, getObjectStoragePath(weblog, fileId)).getResult().getContent();
        return new FileContent(weblog, fileId, null) {
            private InputStream ins = is;
            @Override
            public InputStream getInputStream() {
                return ins;
            }
        };
    }

    private String getObjectStoragePath(Weblog weblog ,String fileId) {
        return '/' + weblog.getHandle() + '/' + fileId;
    }


    public void saveFileContent(Weblog weblog, MediaFile mediaFile)
            throws FileNotFoundException, FilePathException, FileIOException {

        log.info("==========saveFileContent start ->" + mediaFile.getId());

        ObjectMetadata objectMetadata = new ObjectMetadata();
        objectMetadata.setContentType(mediaFile.getContentType());
        objectMetadata.setContentLength(mediaFile.getLength());

        PutObjectRequest request = new PutObjectRequest(bucket, 
                getObjectStoragePath(weblog, mediaFile.getId()), 
                mediaFile.getInputStream(), 
                objectMetadata);

        ObjectMetadata result = baiduBCS.putObject(request).getResult();
        log.info(result);
        baiduBCS.putObjectPolicy(bucket, getObjectStoragePath(weblog, mediaFile.getId()),X_BS_ACL.PublicRead);

        log.info("==========saveFileContent end");

    }


    /**
     * @see org.apache.roller.weblogger.model.FileContentManager#deleteFile(weblog, java.lang.String)
     */
    public void deleteFile(Weblog weblog, String fileId) 
            throws FileNotFoundException, FilePathException, FileIOException {

        log.info("==========deleteFile start:" + fileId);

        Empty result = baiduBCS.deleteObject(bucket, getObjectStoragePath(weblog, fileId)).getResult();
        baiduBCS.deleteObject(bucket, getObjectStoragePath(weblog, fileId) + "_sm").getResult();

        log.info(result);

        log.info("==========deleteFile start");

    }


    /**
     * @see org.apache.roller.weblogger.model.FileContentManager#overQuota(weblog)
     */
    public boolean overQuota(Weblog weblog) {

        return false;
    }



    @Override
    public boolean canSave(Weblog weblog, String fileName, String contentType,
            long size, RollerMessages messages) {

        return true;
    }



}

改动ioc注入：

JPAWebloggerModule.java

if(WebloggerConfig.getBooleanProperty("enabled.use.baiduyun")) {
          binder.bind(FileContentManager.class).to(  BaiduYunFileContentManagerImpl.class);
        }
        else {
          binder.bind(FileContentManager.class).to(  FileContentManagerImpl.class);
        }

最后想说的是这种方法參数设计不太好，应该把MediaFile作为參数。而非用其个别字段（fileId和inputstream）

public void saveFileContent(Weblog weblog,
            String fileId,
            InputStream is)
            throws FileNotFoundException, FilePathException, FileIOException;

这样，roller就能够把百度bcs作为存储图片的server了。