hibernate普通字段延迟加载无效的解决办法

来源：软文情感网

关联对象的延迟加载就不说了，大家都知道。关于普通字段的延迟加载，尤其是lob字段，若没有延迟加载，对性能影响极大。然而简单的使用 @Basic(fetch = FetchType.LAZY) 注解并没有效果。hibernate对此的解释是Lazy property loading requires buildtime byt

关联对象的延迟加载就不说了，大家都知道。

关于普通字段的延迟加载，尤其是lob字段，若没有延迟加载，对性能影响极大。然而简单的使用 @Basic(fetch = FetchType.LAZY) 注解并没有效果。hibernate对此的解释是Lazy property loading requires buildtime bytecode instrumentation. If your persistent classes are not enhanced, Hibernate will ignore lazy property settings and return to immediate fetching.

而bytecode instrumentation的介绍可以参考http://www.correlsense.com/blog/java-bytecode-instrumentation-an-introduction/，本文不多作介绍。

正是因为我们的persistent classes没有使用bytecode instrumentation增强，才导致了普通字段无法延迟加载。

因此要改写一下。以下为一个使用了bytecode instrumentation的持久类：

public class PublicSchemeTaskFile implements java.io.Serializable , FieldHandled {
 // Fields 

 /**
	 * 
	 */
 private static final long serialVersionUID = -82979125820802249L;
 private Integer id;
 private PublicTask publicSchemeTask;
 private Integer fileType;
 private String fileName;
 private byte[] content;
 
 private FieldHandler fieldHandler;//用于延迟加载表字段，关联对象延迟加载的话无需此技术
 	
 	@JSON(serialize = false)
 	public FieldHandler getFieldHandler() {
 	return fieldHandler;
 	}

 	public void setFieldHandler(FieldHandler fieldHandler) {
 	this.fieldHandler = fieldHandler;
 	}
 // Constructors

 /** default constructor */
 public PublicSchemeTaskFile() {
 }

	/** minimal constructor */
 public PublicSchemeTaskFile(Integer id) {
 this.id = id;
 }

	// Property accessors
 @Id 
 
 @Column(name="ID", unique=true, nullable=false, precision=22, scale=0)
 @GeneratedValue(strategy=GenerationType.SEQUENCE,generator = "PUBLIC_SCHEME_TASK_FILE_SEQ")
 public Integer getId() {
 return this.id;
 }
 
 public void setId(Integer id) {
 this.id = id;
 }
 @JSON(serialize = false)
	@ManyToOne(fetch=FetchType.LAZY)
 @JoinColumn(name="PUBLIC_TASK_ID")

 public PublicTask getPublicSchemeTask() {
 return this.publicSchemeTask;
 }
 
 public void setPublicSchemeTask(PublicTask publicSchemeTask) {
 this.publicSchemeTask = publicSchemeTask;
 }
 
 @Column(name="FILE_TYPE", precision=22, scale=0)

 public Integer getFileType() {
 return this.fileType;
 }
 
 public void setFileType(Integer fileType) {
 this.fileType = fileType;
 }
 
 @Column(name="FILE_NAME", length=50)

 public String getFileName() {
 return this.fileName;
 }
 
 public void setFileName(String fileName) {
 this.fileName = fileName;
 }
 @JSON(serialize = false)
 @Lob
 @Basic(fetch = FetchType.LAZY) 
 @Column(name="CONTENT")

 public byte[] getContent() {
 	 if (fieldHandler != null) {
	 return (byte[]) fieldHandler.readObject(this, "content", content);
	 }
	 return null;
 }
 
 public void setContent(byte[] content) {
 this.content = content;
 }

	@Override
	public int hashCode() {
	final int prime = 31;
	int result = 1;
	result = prime * result + ((id == null) ? 0 : id.hashCode());
	return result;
	}

	@Override
	public boolean equals(Object obj) {
	if (this == obj)
	return true;
	if (obj == null)
	return false;
	if (getClass() != obj.getClass())
	return false;
	PublicSchemeTaskFile other = (PublicSchemeTaskFile) obj;
	if (id == null) {
	if (other.id != null)
	return false;
	} else if (!id.equals(other.id))
	return false;
	return true;
	}
}

关键在于FieldHandled接口和lob字段的getter

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hibernate普通字段延迟加载无效的解决办法