关联对象的延迟载入就不说了。大家都知道。

关于普通字段的延迟载入,尤其是lob字段,若没有延迟载入,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的介绍能够參考http://www.correlsense.com/blog/java-bytecode-instrumentation-an-introduction/,本文不多作介绍。

正是由于我们的persistent classes没有使用bytecode instrumentation增强,才导致了普通字段无法延迟载入。

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

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

    // Fields

     /**
*
*/
private static final long serialVersionUID = -8297912895820802249L;
private Integer id;
private PublicTask publicSchemeTask;
private Integer fileType;
private String fileName;
private byte[] content; private FieldHandler fieldHandler;//用于延迟载入表字段。关联对象延迟载入的话无需此技术 @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

05-11 09:41
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