在 Java 迁移中实施校验和

Question

我的 Java 迁移目前没有实现 MigrationChecksumProvider 接口。我想知道他们是否应该这样做。

我不明白校验和在 Flyway 中起什么作用。请有人向我解释一下吗？此外，如果我实施 MigrationChecksumProvider，应该如何计算给定迁移的校验和？

谢谢。

Answer 1

校验和用于迁移的（意外）更改检测，这将使对架构可以准确重新创建的保证失效。

对于 Java 迁移，天空是您所能做的极限。因此，您可以决定如何实施校验和来检测更改。

Answer 2

我想大多数时候你想根据相关 class 文件的内容来计算校验和。我们是这样做的....

import java.io.IOException;
import java.io.InputStream;
import java.util.zip.CRC32;

import org.flywaydb.core.api.migration.jdbc.JdbcMigration;
import org.flywaydb.core.internal.util.FileCopyUtils;
import org.flywaydb.core.internal.util.logging.Log;
import org.flywaydb.core.internal.util.logging.LogFactory;

/**
 * Utility class for checksum calculations.
 * 
 */
public final class Checksums {

    private static final Log LOG = LogFactory.getLog(Checksums.class);

    private Checksums() {
        super(); // singleton
    }

    /**
     * Calculates a checksum based on the given JdbcMigration. It builds the checksum from the byte content of the given
     * migration class file using the same {@link CRC32} method as used by
     * {@link org.flywaydb.core.internal.resolver.sql.SqlMigrationResolver}
     * 
     * @param migration
     * @return the checksum
     */
    public static final Integer checksum(JdbcMigration migration) {
        Integer checksum = null;

        Class<?> migrationClass = migration.getClass();
        String migrationClassFilePath = migrationClass.getName().replace(".", System.getProperty("file.separator")) + ".class";
        InputStream inputStream = null;

        try {
            inputStream = ClassLoader.getSystemResourceAsStream(migrationClassFilePath);
            byte[] classContent = FileCopyUtils.copyToByteArray(inputStream);
            final CRC32 crc32 = new CRC32();
            crc32.update(classContent);
            checksum = (int) crc32.getValue();
        } catch (IOException ioe) {
            LOG.error("Problem calculating checksum for class " + migrationClass.getName(), ioe);
        } finally {
            if (inputStream != null) {
                try {
                    inputStream.close();
                } catch (IOException ioe) {
                    LOG.error("Problem closing input stream to " + migrationClassFilePath, ioe);
                }
            }
        }
        return checksum;
    }    
}

然后你可以创建一个看起来像

的基础class

public abstract class JdbcMigrationWithChecksum implements JdbcMigration, MigrationChecksumProvider {

    @Override
    public Integer getChecksum() {
        return Checksums.checksum(this);
    }
}

在 Java 迁移中实施校验和

Implementing checksums in Java migrations

flyway