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Highperformance Java Persistence Pdf 12


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Vlad Mihalcea is a Java Champion and one of the top Hibernate ORM project committers. He created the Hypersistence Optimizer tool, which scans your application configuration and mappings and tells you what changes you need to make to speed up your data access layer.


Writing a book is difficult, but writing a book about performance and persistence is a real challenge. If you want to understand how locking, sharding, replication, database concurrency control work, then this book is for you. Vlad gives you plenty of tips and tricks on Hibernate, helping you diagnose your performance issues (e.g. mapping, fetching, or caching). I learn a lot by reading his book and I highly recommend it if you use relational databases and ORM tools such as Hibernate.


Good books on persistence are few and far between. This is something else - it's deeply researched but also entirely practical. I'm basically using it as a reference for everything SQL. Plus, the transaction chapter is a must read.


Behind the scenes, the Hibernate Session wraps a JDBC java.sql.Connection and acts as a factory for org.hibernate.Transaction instances.It maintains a generally "repeatable read" persistence context (first level cache) of the application domain model.


Ultimately the application domain model is the central character in an ORM.They make up the classes you wish to map. Hibernate works best if these classes follow the Plain Old Java Object (POJO) / JavaBean programming model.However, none of these rules are hard requirements.Indeed, Hibernate assumes very little about the nature of your persistent objects. You can express a domain model in other ways (using trees of java.util.Map instances, for example).


Strictly speaking, a basic type is denoted by the javax.persistence.Basic annotation.Generally speaking, the @Basic annotation can be ignored, as it is assumed by default.Both of the following examples are ultimately the same.


We said before that a Hibernate type is not a Java type, nor an SQL type, but that it understands both and performs the marshalling between them.But looking at the basic type mappings from the previous examples,how did Hibernate know to use its org.hibernate.type.StringType for mapping for java.lang.String attributes,or its org.hibernate.type.IntegerType for mapping java.lang.Integer attributes


As an example, take a String attribute such as we saw before with Product#sku.Since there was no explicit type mapping, Hibernate looks to the BasicTypeRegistry to find the registered mapping for java.lang.String.This goes back to the "BasicTypeRegistry key(s)" column we saw in the tables at the start of this chapter.


Hibernate makes it relatively easy for developers to create their own basic type mappings type.For example, you might want to persist properties of type java.util.BigInteger to VARCHAR columns, or support completely new types.


The AbstractSingleColumnStandardBasicType requires an sqlTypeDescriptor and a javaTypeDescriptor.The sqlTypeDescriptor is VarcharTypeDescriptor.INSTANCE because the database column is a VARCHAR.On the Java side, we need to use a BitSetTypeDescriptor instance which can be implemented like this:


The original JPA-compliant way to map enums was via the @Enumerated or @MapKeyEnumerated for map keys annotations, working on the principle that the enum values are stored according to one of 2 strategies indicated by javax.persistence.EnumType:


While the java.sql classes define a direct association to the SQL Date/Time data types,the java.util or java.time properties need to explicitly mark the SQL type correlation with the @Temporal annotation.This way, a java.util.Date or a java.util.Calendar can be mapped to either an SQL DATE, TIME or TIMESTAMP type.


By default, Hibernate is going to use the PreparedStatement.setTimestamp(int parameterIndex, java.sql.Timestamp) orPreparedStatement.setTime(int parameterIndex, java.sql.Time x) when saving a java.sql.Timestamp or a java.sql.Time property.


With this configuration pr




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