java注解（一）概念及JABX使用例子

一、概念____________________________________________________________

 

注解，作用类似有xml配置文件，避免同一份信息保存在两个地方。

@Override,@Deprecated (key,value)都省略了

@Retention(RetentionPolicy.RUNTIME)只有一个键时，key可以省略

@SupressWarnings({"uncheck", "unused"})大括号表示数组类型，key只有一个，省略

@XmlElement(name = "id")配置参数，键值对

 

 

注解用@interface用来声明定义，元注解，在java.lang.annotation包里面，有4个

 

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Documented {//are to be documented by javadoc and similar tools by default
}

 

 

@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Inherited {//
}

 

 

//@Retention保留策略: CLASS、RUNTIME和SOURCE,分别表示注解保存在类文件、JVM运行时刻和源代码中。 
//只有RUNTIME，才能在运行时刻通过反射API来获取到注解的信息，类似SSH的xml配置文件的注入作用  
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Retention {
    RetentionPolicy value();
}

 

 

//@Target用来声明注解的作用范围，如类型、方法和域等
@Documented
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.ANNOTATION_TYPE)
public @interface Target {
    ElementType[] value();
}

 

二、JAXB例子____________________________________________________________

 

JAXB（Java Architecture for XML Binding) 

 

/**
 * @author timeriver.wang
 * @date 2013-01-09 8:07:01 PM
 */
@XmlRootElement
@XmlAccessorType(XmlAccessType.PROPERTY)
public class Student {
	private String id;
	private String name;
	public String getId() {
		return id;
	}
	@XmlElement(name = "id")
	public void setId(String id) {
		this.id = id;
	}
	@XmlElement(name = "name")
	public String getName() {
		return name;
	}
	public void setName(String name) {
		this.name = name;
	}
}

 

 

/**
 * @author timeriver.wang
 * @date 2013-01-09 8:07:09 PM
 */
@XmlRootElement
public class Teacher {
    private String id;
    private String name;
    private List<Student>students;
    @XmlAttribute (name = "tid")  
    public String getId() {
        return id;
    }
    public void setId( String id ) {
        this.id = id;
    }
    @XmlElement(name = "tname")
    public String getName() {
        return name;
    }
    public void setName( String name ) {
        this.name = name;
    }
    @XmlElement(name = "students")
    public List<Student> getStudents() {
        return students;
    }
    public void setStudents( List<Student> students ) {
        this.students = students;
    }
}

 

 

/**
 * @author timeriver.wang
 * @date 2013-01-09 8:08:15 PM
 */
public class Test {
    public static void main( String[] args )throws Exception {
//        toXml();
//        toStu();
        toXmls();
    }

    public static void toXml()throws Exception {
        Student stu = new Student();
        stu.setId( "007" );
        stu.setName( "zhouxingxing" );

        File file = new File( "D:/stu.xml" );
        JAXBContext jaxbContext = JAXBContext.newInstance( Student.class );

        Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

        jaxbMarshaller.setProperty( Marshaller.JAXB_FORMATTED_OUTPUT, true );

        jaxbMarshaller.marshal( stu, file );
        jaxbMarshaller.marshal( stu, System.out );
    }

    public static void toStu()throws Exception {
        File file = new File( "D:/stu.xml" );
        JAXBContext jaxbContext = JAXBContext.newInstance( Student.class );
        Unmarshaller jaxbUnmarshaller = jaxbContext.createUnmarshaller();
        Student stu = (Student) jaxbUnmarshaller.unmarshal( file );
        System.out.println( stu );
    }

    public static void toXmls()throws Exception {
        Student stu = new Student();
        stu.setId( "007" );
        stu.setName( "zhouxingxing" );
        Student stu2 = new Student();
        stu2.setId( "008" );
        stu2.setName( "dawenxi" );
        List<Student>students = new ArrayList<Student>();
        students.add( stu );
        students.add( stu2 );
        Teacher teacher = new Teacher();
        teacher.setId( "101" );
        teacher.setName( "DASHI" );
        teacher.setStudents( students );
        File file = new File( "D:/teacher.xml" );
        JAXBContext jaxbContext = JAXBContext.newInstance( Teacher.class );

        Marshaller jaxbMarshaller = jaxbContext.createMarshaller();

        jaxbMarshaller.setProperty( Marshaller.JAXB_FORMATTED_OUTPUT, true );

        jaxbMarshaller.marshal( teacher, file );
        jaxbMarshaller.marshal( teacher, System.out );
    }
}