注解學(xué)習(xí)(模仿springMvc的注解注入方式)

2019-11-14 15:39:44

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最近在看sPRingMvc的源碼，看到了該框架的注入注解的部分覺的有點(diǎn)吃力，可能還是對(duì)注解的方面的知識(shí)還認(rèn)識(shí)的不夠深刻，所以特意去學(xué)習(xí)注解方面的知識(shí)。由于本人也是抱著學(xué)習(xí)的態(tài)度來閱讀源碼，若文章在表述和代碼方面如有不妥之處，歡迎批評(píng)指正。留下你的腳印，歡迎評(píng)論！希望能互相學(xué)習(xí)。

1，首先定義三個(gè)常用的注解Service，Autowired，Contrller；(主要的解釋都在代碼中有，在這里就不多陳述)

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：指定注解的使用范圍(指的是，在哪些類型可以使用該注解：Service注解只能在類，接口（包括注解類型）或enum等使用) * 可選值： * 可選的值在枚舉類 ElemenetType 中，包括：           ElemenetType.CONSTRUCTOR 構(gòu)造器聲明           ElemenetType.FIELD 域聲明（包括 enum 實(shí)例）           ElemenetType.LOCAL_VARIABLE 局部變量聲明          ElemenetType.ANNOTATION_TYPE 作用于注解量聲明          ElemenetType.METHOD 方法聲明          ElemenetType.PACKAGE 包聲明           ElemenetType.PARAMETER 參數(shù)聲明           ElemenetType.TYPE 類，接口（包括注解類型）或enum聲明  * */@Target(ElementType.TYPE)/*Description: * @Retention ：表示在什么級(jí)別保存該注解信息 * 可選的參數(shù)值在枚舉類型 RetentionPolicy 中，包括：           RetentionPolicy.SOURCE 注解將被編譯器丟棄           RetentionPolicy.CLASS 注解在class文件中可用，但會(huì)被VM丟棄           RetentionPolicy.RUNTIME VM將在運(yùn)行期也保留注釋，因此可以通過反射機(jī)制讀取注解的信息。  * */@Retention(RetentionPolicy.RUNTIME)/*@Documented 將此注解包含在 javadoc 中 ，它代表著此注解會(huì)被javadoc工具提取成文檔。 * 在doc文檔中的內(nèi)容會(huì)因?yàn)榇俗⒔獾男畔?nèi)容不同而不同。相當(dāng)與@see,@param 等。 * */@Documentedpublic @interface Service {    /* @interface用來聲明一個(gè)注解，其中的每一個(gè)方法實(shí)際上是聲明了一個(gè)配置參數(shù)。     * 方法的名稱就是參數(shù)的名稱，返回值類型就是參數(shù)的類型（返回值類型只能是基本類型、Class、String、enum）。     * 可以通過default來聲明參數(shù)的默認(rèn)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";}

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2：javaBean數(shù)據(jù)池-BeanFactory：主要存放含有注解的類；

package com.lishun.factory;import java.util.HashMap;import java.util.Map;/** * Description:存放所有bean的數(shù)據(jù)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("未注入的類型:" + beanName);        }    }    public static Boolean containsBean(String beanName){        return map.containsKey(beanName);    }}

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3:編寫處理注解的核心代碼(這里涉及的主要知識(shí)是反射，如果反射知識(shí)不夠熟練的話建議先學(xué)習(xí)反射方面的知識(shí))，主要涉及的兩個(gè)類是注解驅(qū)動(dòng)(AnnotationDriven)和注解掃描類(PackUtils-這個(gè)類主要的是掃描包名下所有的類(如com.lishun，就是掃描該包下所有的類)，代碼主要是來自網(wǎng)絡(luò))

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:注入驅(qū)動(dòng)類，所有的注解注入都在這里實(shí)現(xiàn)(這里只實(shí)現(xiàn)了通過類型來注入值，其他方式?jīng)]實(shí)現(xiàn)，其實(shí)代碼都是差不多了，有興趣的可以自行腦補(bǔ)) * @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();                //掃描的到的含有注解的類實(shí)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());            //判斷存放bean的池中是否存在該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) {                    // 判斷是否是通過類型注解注入                    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:掃描指定包工具類的注解 * @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("http://.", "/"));            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;    }    // 獲取指定包名下的所有類（可根據(jù)注解進(jìn)行過濾）    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("http://.", "/"));            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();        }    }}

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4 最后編寫平時(shí)使用的設(shè)計(jì)模式來測(cè)試注解(Dao,Service,Contrller)【這里主要是為測(cè)試注解的注入，所以沒有使用實(shí)際的使用數(shù)據(jù)庫(kù)數(shù)據(jù)，側(cè)重點(diǎn)不在這里】

Dao

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

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();    }}

測(cè)試入口

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 {        //啟動(dòng)時(shí)根據(jù)需要掃描的包名，來注入含有注解的類的字段值        AnnotationDriven.annotationDriven("com.lishun");        //這里相當(dāng)于web的訪問一次controller的一次請(qǐng)求        UserContrller user = (UserContrller) BeanFactory                .getBean("com.lishun.controller.UserContrller");        user.login();    }}