你的位置:首页 > Java教程

[Java教程]注解学习(模仿springMvc的注解注入方式)


最近在看springMvc的源码,看到了该框架的注入注解的部分觉的有点吃力,可能还是对注解的方面的知识还认识的不够深刻,所以特意去学习注解方面的知识。由于本人也是抱着学习的态度来阅读源码,若文章在表述和代码方面如有不妥之处,欢迎批评指正。留下你的脚印,欢迎评论!希望能互相学习。

1,首先定义三个常用的注解Service,Autowired,Contrller;(主要的解释都在代码中有,在这里就不多陈述)

Service:

package com.lishun.Annotation;import java.lang.annotation.Documented;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;/*Description: * @Target:指定注解的使用范围(指的是,在哪些类型可以使用该注解:Service注解只能在类,接口(包括注解类型)或enum等使用) * 可选值: * 可选的值在枚举类 ElemenetType 中,包括:      ElemenetType.CONSTRUCTOR 构造器声明      ElemenetType.FIELD 域声明(包括 enum 实例)      ElemenetType.LOCAL_VARIABLE 局部变量声明     ElemenetType.ANNOTATION_TYPE 作用于注解量声明     ElemenetType.METHOD 方法声明     ElemenetType.PACKAGE 包声明      ElemenetType.PARAMETER 参数声明      ElemenetType.TYPE 类,接口(包括注解类型)或enum声明 * */@Target(ElementType.TYPE)/*Description: * @Retention :表示在什么级别保存该注解信息 * 可选的参数值在枚举类型 RetentionPolicy 中,包括:      RetentionPolicy.SOURCE 注解将被编译器丢弃      RetentionPolicy.CLASS 注解在class文件中可用,但会被VM丢弃      RetentionPolicy.RUNTIME VM将在运行期也保留注释,因此可以通过反射机制读取注解的信息。 * */@Retention(RetentionPolicy.RUNTIME)/*@Documented 将此注解包含在 javadoc 中 ,它代表着此注解会被javadoc工具提取成文档。 * 在doc文档中的内容会因为此注解的信息内容不同而不同。相当与@see,@param 等。 * */@Documentedpublic @interface Service {  /* @interface用来声明一个注解,其中的每一个方法实际上是声明了一个配置参数。   * 方法的名称就是参数的名称,返回值类型就是参数的类型(返回值类型只能是基本类型、Class、String、enum)。   * 可以通过default来声明参数的默认值。  */  String value() default "this is service annotation";}

 

Autowired:

package com.lishun.Annotation;import java.lang.annotation.Documented;import java.lang.annotation.ElementType;import java.lang.annotation.Inherited;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;@Target({ElementType.METHOD,ElementType.FIELD}) @Retention(RetentionPolicy.RUNTIME) public @interface Autowired {   public String value() default "no description"; }

Contrller:

package com.lishun.Annotation;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 Contrller {  String value() default "this is contrller annotation";}

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

2:javaBean数据池-BeanFactory:主要存放含有注解的类;

package com.lishun.factory;import java.util.HashMap;import java.util.Map;/** * Description:存放所有bean的数据池 * @author lishun * @since 2015-09-10 */public class BeanFactory {  private static Map<String, Object> map = new HashMap<String, Object>();  public static void addBean(String beanName, Object bean) {    map.put(beanName, bean);  }  public static Object getBean(String beanName) throws Exception {    Object o = map.get(beanName);    if (o != null) {      return o;    } else {      throw new Exception("未注入的类型:" + beanName);    }  }  public static Boolean containsBean(String beanName){    return map.containsKey(beanName);  }}

 

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

3:编写处理注解的核心代码(这里涉及的主要知识是反射,如果反射知识不够熟练的话建议先学习反射方面的知识),主要涉及的两个类是注解驱动(AnnotationDriven)和注解扫描类(PackUtils-这个类主要的是扫描包名下所有的类(如com.lishun,就是扫描该包下所有的类),代码主要是来自网络)

AnnotationDriven:

package com.lishun.utils;import java.lang.annotation.Annotation;import java.lang.reflect.Field;import java.util.List;import com.lishun.Annotation.Autowired;import com.lishun.Annotation.Contrller;import com.lishun.Annotation.Service;import com.lishun.factory.BeanFactory;/** * Description:注入驱动类,所有的注解注入都在这里实现(这里只实现了通过类型来注入值,其他方式没实现,其实代码都是差不多了,有兴趣的可以自行脑补) * @author lishun * */public class AnnotationDriven {  public static void annotationDriven(String packName) throws Exception {    //注入Service和Contrller    List<Class<?>> classSaveServicePaths = PackUtils        .getClassListByAnnotation(packName, Service.class);    List<Class<?>> classSaveContrllerPaths = PackUtils        .getClassListByAnnotation(packName, Contrller.class);    saveBean(classSaveServicePaths);    saveBean(classSaveContrllerPaths);    //注入Autowired    List<Class<?>> classInjectPaths = PackUtils.getClassListByAnnotation(        packName, Autowired.class);    inject(classInjectPaths);  }  private static void saveBean(List<Class<?>> classSavePaths)      throws InstantiationException, IllegalAccessException {    for (Class<?> classPath : classSavePaths) {      try {        Class c = Class.forName(classPath.getName());        Object o = c.newInstance();        //扫描的到的含有注解的类实例化后保存在池中        BeanFactory.addBean(classPath.getName(), o);      } catch (ClassNotFoundException e) {        e.printStackTrace();      }    }  }  private static void inject(List<Class<?>> classInjectPaths) throws Exception {    Object o = null;    for (Class<?> classInjectPath : classInjectPaths) {      Class c = Class.forName(classInjectPath.getName());      //判断存放bean的池中是否存在该bean      if (BeanFactory.containsBean(classInjectPath.getName())) {        o = BeanFactory.getBean(classInjectPath.getName());      } else {        o = c.newInstance();      }      Field[] fields = c.getDeclaredFields();      for (Field field : fields) {        Annotation[] annotations = field.getAnnotations();        for (Annotation annotation : annotations) {          // 判断是否是通过类型注解注入          if (annotation instanceof Autowired) {            Class classField = field.getType();            Object clazz = BeanFactory                .getBean(classField.getName());            field.set(o, clazz);            BeanFactory.addBean(classInjectPath.getName(), o);          }        }      }    }  }}

PackUtils:

package com.lishun.utils;import java.io.File;import java.io.FileFilter;import java.lang.annotation.Annotation;import java.lang.reflect.Field;import java.net.JarURLConnection;import java.net.URL;import java.util.ArrayList;import java.util.Enumeration;import java.util.List;import java.util.jar.JarEntry;import java.util.jar.JarFile;/** * Description:扫描指定包工具类的注解 * @author lishun * @since 2015-09-10 */public class PackUtils {  public static List<Class<?>> getClassList(String packageName, boolean isRecursive) {    List<Class<?>> classList = new ArrayList<Class<?>>();    try {      Enumeration<URL> urls = Thread.currentThread().getContextClassLoader().getResources(packageName.replaceAll("\\.", "/"));      while (urls.hasMoreElements()) {        URL url = urls.nextElement();        if (url != null) {          String protocol = url.getProtocol();          if (protocol.equals("file")) {            String packagePath = url.getPath();            addClass(classList, packagePath, packageName, isRecursive);          } else if (protocol.equals("jar")) {            JarURLConnection jarURLConnection = (JarURLConnection) url.openConnection();            JarFile jarFile = jarURLConnection.getJarFile();            Enumeration<JarEntry> jarEntries = jarFile.entries();            while (jarEntries.hasMoreElements()) {              JarEntry jarEntry = jarEntries.nextElement();              String jarEntryName = jarEntry.getName();              if (jarEntryName.endsWith(".class")) {                String className = jarEntryName.substring(0, jarEntryName.lastIndexOf(".")).replaceAll("/", ".");                if (isRecursive || className.substring(0, className.lastIndexOf(".")).equals(packageName)) {                  classList.add(Class.forName(className));                }              }            }          }        }      }    } catch (Exception e) {      e.printStackTrace();    }    return classList;  }  // 获取指定包名下的所有类(可根据注解进行过滤)  public static List<Class<?>> getClassListByAnnotation(String packageName, Class<? extends Annotation> annotationClass) {    List<Class<?>> classList = new ArrayList<Class<?>>();    try {      Enumeration<URL> urls = Thread.currentThread().getContextClassLoader().getResources(packageName.replaceAll("\\.", "/"));      while (urls.hasMoreElements()) {        URL url = urls.nextElement();        if (url != null) {          String protocol = url.getProtocol();          if (protocol.equals("file")) {            String packagePath = url.getPath();            addClassByAnnotation(classList, packagePath, packageName, annotationClass);          } else if (protocol.equals("jar")) {            JarURLConnection jarURLConnection = (JarURLConnection) url.openConnection();            JarFile jarFile = jarURLConnection.getJarFile();            Enumeration<JarEntry> jarEntries = jarFile.entries();            while (jarEntries.hasMoreElements()) {              JarEntry jarEntry = jarEntries.nextElement();              String jarEntryName = jarEntry.getName();              if (jarEntryName.endsWith(".class")) {                String className = jarEntryName.substring(0, jarEntryName.lastIndexOf(".")).replaceAll("/", ".");                Class<?> cls = Class.forName(className);                if (cls.isAnnotationPresent(annotationClass)) {                  classList.add(cls);                }              }            }          }        }      }    } catch (Exception e) {      e.printStackTrace();    }    return classList;  }  private static void addClass(List<Class<?>> classList, String packagePath, String packageName, boolean isRecursive) {    try {      File[] files = getClassFiles(packagePath);      if (files != null) {        for (File file : files) {          String fileName = file.getName();          if (file.isFile()) {            String className = getClassName(packageName, fileName);            classList.add(Class.forName(className));          } else {            if (isRecursive) {              String subPackagePath = getSubPackagePath(packagePath, fileName);              String subPackageName = getSubPackageName(packageName, fileName);              addClass(classList, subPackagePath, subPackageName, isRecursive);            }          }        }      }    } catch (Exception e) {      e.printStackTrace();    }  }  private static File[] getClassFiles(String packagePath) {    return new File(packagePath).listFiles(new FileFilter() {      @Override      public boolean accept(File file) {        return (file.isFile() && file.getName().endsWith(".class")) || file.isDirectory();      }    });  }  private static String getClassName(String packageName, String fileName) {    String className = fileName.substring(0, fileName.lastIndexOf("."));    if (!packageName.equals("")) {      className = packageName + "." + className;    }    return className;  }  private static String getSubPackagePath(String packagePath, String filePath) {    String subPackagePath = filePath;    if (!packagePath.equals("")) {      subPackagePath = packagePath + "/" + subPackagePath;    }    return subPackagePath;  }  private static String getSubPackageName(String packageName, String filePath) {    String subPackageName = filePath;    if (!packageName.equals("")) {      subPackageName = packageName + "." + subPackageName;    }    return subPackageName;  }  private static void addClassByAnnotation(List<Class<?>> classList, String packagePath, String packageName, Class<? extends Annotation> annotationClass) {    try {      File[] files = getClassFiles(packagePath);      if (files != null) {        for (File file : files) {          String fileName = file.getName();          if (file.isFile()) {            String className = getClassName(packageName, fileName);            Class<?> cls = Class.forName(className);            if (cls.isAnnotationPresent(annotationClass)) {              classList.add(cls);            }            Field[] fields=cls.getFields();            for (Field field : fields) {              if(field.isAnnotationPresent(annotationClass)){                 classList.add(cls);              }            }          } else {            String subPackagePath = getSubPackagePath(packagePath, fileName);            String subPackageName = getSubPackageName(packageName, fileName);            addClassByAnnotation(classList, subPackagePath, subPackageName, annotationClass);          }        }      }    } catch (Exception e) {      e.printStackTrace();    }  }}

 

------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

4 最后编写平时使用的设计模式来测试注解(Dao,Service,Contrller)【这里主要是为测试注解的注入,所以没有使用实际的使用数据库数据,侧重点不在这里】

Dao

package com.lishun.Dao;import com.lishun.Annotation.Service;@Servicepublic class UserDao {  public void run(){    System.out.println("测试成功");  }}

Service:

package com.lishun.Service;import com.lishun.Annotation.Autowired;import com.lishun.Annotation.Service;import com.lishun.Dao.UserDao;@Servicepublic class UserService {  @Autowired  public UserDao userDao;  public void run(){     userDao.run();  }}

Controller:

package com.lishun.controller;import com.lishun.Annotation.Autowired;import com.lishun.Annotation.Contrller;import com.lishun.Service.UserService;@Contrllerpublic class UserContrller {  @Autowired  public UserService userService;  public void login(){    userService.run();  }}

测试入口

package com.lishun.t;import java.lang.annotation.Annotation;import java.lang.reflect.Field;import java.lang.reflect.InvocationHandler;import java.lang.reflect.Method;import java.lang.reflect.Proxy;import java.util.Arrays;import java.util.List;import org.junit.Test;import com.lishun.Annotation.Autowired;import com.lishun.Annotation.Contrller;import com.lishun.Annotation.Service;import com.lishun.Dao.UserDao;import com.lishun.Service.UserService;import com.lishun.controller.UserContrller;import com.lishun.factory.BeanFactory;import com.lishun.utils.AnnotationDriven;import com.lishun.utils.PackUtils;public class test {  @Test  public void main() throws Exception {    //启动时根据需要扫描的包名,来注入含有注解的类的字段值    AnnotationDriven.annotationDriven("com.lishun");    //这里相当于web的访问一次controller的一次请求    UserContrller user = (UserContrller) BeanFactory        .getBean("com.lishun.controller.UserContrller");    user.login();  }}

最后运行,

控制台输出:测试成功

由于本人水平有限,若文章在表述和代码方面如有不妥之处,欢迎批评指正。留下你的脚印,欢迎评论!希望能互相学习。需要源码的留下邮箱