java 注解的使用

项目会经常解析properies文件，根据key获得value，下面写一个如何使用注解的方式来获得value
1. AnnotateProperties类：用来获得properties文件的路径

package AnnotateSrc;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
public @interface AnnotateProperties {
    String value();
    String key() default "";

}

2.Property类：用来记录键值对

package AnnotateSrc;

import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ ElementType.FIELD })
@Retention(RetentionPolicy.RUNTIME)
public @interface Property {

	String key();
	
	String defaultValue() default "";

}

3.Annotate：JavaBean使用注解的方式声明properties文件存放的路径

package test;

import AnnotateSrc.AnnotateProperties;
import AnnotateSrc.Property;

[color=red]@AnnotateProperties(value = "test.properties", key = "C:\\")[/color]
public class Annotate {    
    @Property(key = "header")
    private String header_;

    public String getHeader() {
        return header_;
    }

    public void setHeader(String header) {
        this.header_ = header;
    }
}

4.Test ：测试类

package test;

import java.io.BufferedInputStream;
import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import AnnotateSrc.AnnotateProperties;
import java.util.Properties;

public class Test {

    /**
     * @param args
     * @throws Exception 
     */
    public static void main(String[] args) throws Exception {
        AnnotateProperties annotationProperties = Annotate.class
        .getAnnotation(AnnotateProperties.class);
        String propertiesName = annotationProperties.value();
        String dir = annotationProperties.key();
        System.out.println(dir+propertiesName);
        File f = new File(dir+"\\"+propertiesName);
        Properties pro = readProperties(f);
        System.out.println(pro.get("header"));
        
    }
    
    private static Properties readProperties(File file) throws Exception {
        BufferedInputStream bis = null;
        Properties prop = null;
        try {
            bis = new BufferedInputStream(new FileInputStream(file));
            prop = new NullableProperties();
            prop.load(bis);
        } catch (FileNotFoundException ex1) {
            throw new Exception(ex1);
        } catch (SecurityException e) {
            throw new Exception(e);
        } catch (Exception ex2) {
            throw new Exception(ex2);
        } finally {
            try {
                if (bis != null) {
                    bis.close();
                }
            } catch (Exception ex) {
            }
        }
        return prop;
    }
    
    public static class NullableProperties extends Properties {
        public String getProperty(String key, String defaultValue) {
            String origin = super.getProperty(key, defaultValue);
            if (origin != null && origin.trim().length() == 0) {
                // 空白
                return defaultValue;
            }
            return origin;
        }
    };
}