手写mini版Spring IOC容器（一）

小鱼儿 2022-04-06 15:16 241阅读 0赞

通常用Spring，我们都是从DispatchServlet开始的。

这个简易的IOC容器主要目的就是模拟IOC将生成的bean注入到IOC容器中。

代码项目的github地址：[https://github.com/harrypitter/CreateSpring.git][https_github.com_harrypitter_CreateSpring.git]

简单类图：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcnJ5cHR0ZXI_size_16_color_FFFFFF_t_70][]

我这边程序中用了jetty runner插件来辅助。

这边需要配置基础的注解:

Autowired:

package com.praticespring.annotation;
    
    import java.lang.annotation.*;
    
    @Target({ElementType.FIELD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface Autowried {
        String value() default  "";
    }

Controller:

package com.praticespring.annotation;
    
    import java.lang.annotation.*;
    
    @Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface Controller {
        String value() default  "";
    }

RequestMapping:

package com.praticespring.annotation;
    
    import java.lang.annotation.*;
    
    @Target({ElementType.TYPE,ElementType.METHOD})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface RequestMapping {
        String value() default  "";
    }

RequestParam:

package com.praticespring.annotation;
    
    import java.lang.annotation.*;
    
    @Target({ElementType.PARAMETER})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface RequestParam {
        String value() default  "";
    }

Serivice:

package com.praticespring.annotation;
    
    import java.lang.annotation.*;
    
    @Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    public @interface Service {
        String value() default  "";
    }

这里引入简单的MVC调用的demoService,暂时没写MVC；

接口IDemoService:

package com.praticespring.mvc.service;
    public interface IDemoService {
    
        public String get(String name);
    
    }

对应的DemoService:

package com.praticespring.mvc.service;
    
    import com.praticespring.annotation.Service;
    
    @Service
    public class DemoService implements IDemoService {
    
        public String get(String name) {
            return "My name is " + name;
        }
    
    }

DemoAction:

package com.praticespring.mvc.action;
    
    import com.praticespring.annotation.Autowried;
    import com.praticespring.annotation.Controller;
    import com.praticespring.annotation.RequestMapping;
    import com.praticespring.annotation.RequestParam;
    import com.praticespring.mvc.service.IDemoService;
    
    import java.io.IOException;
    
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    
    @Controller
    @RequestMapping("/demo")
    public class DemoAction {
    
        @Autowried
        private IDemoService demoService;
    
        @RequestMapping("/query.json")
        public void query(HttpServletRequest req,HttpServletResponse resp,
                          @RequestParam("name") String name){
            String result = demoService.get(name);
            System.out.println(result);
    //		try {
    //			resp.getWriter().write(result);
    //		} catch (IOException e) {
    //			e.printStackTrace();
    //		}
        }
    
        @RequestMapping("/edit.json")
        public void edit(HttpServletRequest req,HttpServletResponse resp,Integer id){
    
        }
    
    }

MyAction:

package com.praticespring.mvc.action;
    
    import com.praticespring.annotation.Autowried;
    import com.praticespring.annotation.Controller;
    import com.praticespring.annotation.RequestMapping;
    import com.praticespring.mvc.service.IDemoService;
    
    @Controller
    public class MyAction {
    
        @Autowried
        IDemoService demoService;
    
        @RequestMapping("/index.html")
        public void query(){
    
        }
    
    }

然后写上资源的propoerty文件：

scanPackage=com.praticespring
    templateRoot=layouts

这边借助了jetty，需要配置相对应的webdefault.xml和web.xml

因为是基础配置，这个就不详细列了，有兴趣的话从上面github地址上下载相关代码看下。

核心的DispatchServlet类：

package com.praticespring.servlet;
    
    import com.praticespring.annotation.Autowried;
    import com.praticespring.annotation.Controller;
    import com.praticespring.annotation.Service;
    
    import javax.servlet.ServletConfig;
    import javax.servlet.ServletException;
    import javax.servlet.http.HttpServlet;
    import javax.servlet.http.HttpServletRequest;
    import javax.servlet.http.HttpServletResponse;
    import java.io.File;
    import java.io.IOException;
    import java.io.InputStream;
    import java.lang.reflect.Field;
    import java.net.URL;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Map;
    import java.util.Properties;
    import java.util.concurrent.ConcurrentHashMap;
    
    public class DispatchServlet extends HttpServlet {
    
        private Properties contextConfig = new Properties();
    
        private Map<String,Object> beanMap = new ConcurrentHashMap<String,Object>();
    
        private List<String> classNames = new ArrayList<String>();
    
        @Override
        protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            this.doPost(req,resp);
        }
    
        @Override
        protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
            System.out.println("---------- 调用doPost ----------");
        }
    
        @Override
        public void init(ServletConfig config) throws ServletException {
            //开始初始化的进程
    
            //定位
            doLoadConfig(config.getInitParameter("contextConfigLocation"));
    
            //加载
            doScanner(contextConfig.getProperty("scanPackage"));
    
            //注册
            doRegistry();
    
            //自动依赖注入
    
            //在Spring中是通过调用getBean方法才出发依赖注入的
            doAutowired();
    
    
    //        DemoAction action = (DemoAction)beanMap.get("demoAction");
    //        action.query(null,null,"Tom");
    
            //如果是SpringMVC会多设计一个HnandlerMapping
    
            //将@RequestMapping中配置的url和一个Method关联上
            //以便于从浏览器获得用户输入的url以后，能够找到具体执行的Method通过反射去调用
            initHandlerMapping();
    
        }
    
        private void initHandlerMapping() {
    
        }
    
        private void doAutowired() {
            if(beanMap.isEmpty()){ return; }
    
            for (Map.Entry<String,Object> entry : beanMap.entrySet()) {
    
                Field[] fields = entry.getValue().getClass().getDeclaredFields();
    
                for (Field field : fields){
    
                    if(!field.isAnnotationPresent(Autowried.class)){continue;}
    
                    Autowried autowried = field.getAnnotation(Autowried.class);
    
                    String beanName = autowried.value().trim();
                    if("".equals(beanName)){
                        beanName = field.getType().getName();
                    }
                    field.setAccessible(true);
    
                    try {
                        field.set(entry.getValue(),beanMap.get(beanName));
                    } catch (IllegalAccessException e) {
                        e.printStackTrace();
                    }
    
                }
    
            }
        }
    
        private void doRegistry() {
            if(classNames.isEmpty()){ return;}
    
            try{
    
                for(String className : classNames){
                    Class<?> clazz = Class.forName(className);
    
    
                    //在Spring中用的多个子方法来处理的
                    if(clazz.isAnnotationPresent(Controller.class)){
    
                        String beanName = lowerFirstCase(clazz.getSimpleName());
    
                        //在Spring中在这个阶段不是不会直接put instance，这里put的是BeanDefinition
                        beanMap.put(beanName,clazz.newInstance());
    
                    }else if(clazz.isAnnotationPresent(Service.class)){
    
                        Service service = clazz.getAnnotation(Service.class);
    
                        //默认用类名首字母注入
                        //如果自己定义了beanName，那么优先使用自己定义的beanName
                        //如果是一个接口，使用接口的类型去自动注入
    
                        //在Spring中同样会分别调用不同的方法 autowriedByName autowritedByType
    
                        String beanName = service.value();
                        if("".equals(beanName.trim())){
                            beanName = lowerFirstCase(clazz.getSimpleName());
                        }
    
                        Object instance = clazz.newInstance();
    
                        beanMap.put(beanName,instance);
    
                        Class<?>[] interfaces = clazz.getInterfaces();
    
                        for (Class<?> i :interfaces){
                            beanMap.put(i.getName(),instance);
                        }
    
                    }else{
                        continue;
                    }
    
                }
    
    
            }catch (Exception e){
                e.printStackTrace();
            }
        }
    
        private void doScanner(String packageName) {
            URL url = this.getClass().getClassLoader().getResource("/" + packageName.replaceAll("\\.","/"));
    
            File classDir = new File(url.getFile());
    
            for (File file : classDir.listFiles()){
                if(file.isDirectory()){
                    doScanner(packageName + "." +file.getName());
                }else {
                    classNames.add(packageName + "." + file.getName().replace(".class",""));
                }
            }
        }
    
        private void doLoadConfig(String location) {
    
            InputStream is = this.getClass().getClassLoader().getResourceAsStream(location.replace("classpath:",""));
    
            try {
                contextConfig.load(is);
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
                try {
                    if(null != is){is.close();}
                }catch (Exception e){
                    e.printStackTrace();
                }
    
            }
    
        }
    
        private String lowerFirstCase(String str){
            char[] strArray = str.toCharArray();
            strArray[0]+= 32;
            return strArray.toString();
        }
    }

这个工程主要目的就是手写这个DispatchServlet类：

IOC的初始过程就是：定位--->加载------>注册------>依赖注入

首先通过doLoadConfig（）方法，定位application.properties文件里面的内容，然后通过doScanner扫描制定路径下的所有文件内容，再我这个程序里面就是扫描com.praticespring文件夹下的所有文件，然后当时文件的时候就在classNames里面添加对应的.class类文件名。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcnJ5cHR0ZXI_size_16_color_FFFFFF_t_70 1][]

扫描完之后，进入 doRegistry（）方法，这个方法就是将对应的bean方法（上面程序里的逻辑是判断classNames里面的方法，如果是Service方法和Controller方法，就放入beanMap里面）放入指定的IOC容器beanMap里面。

以上就是一件很简单的IOC的逻辑了。之后会写一个更详细的IOC容器。另外，以上的debug借助了jetty Runner ，在IntellJ IDEA的Setting->Plugins->Browse repositories里面搜索jetty runner下载

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcnJ5cHR0ZXI_size_16_color_FFFFFF_t_70 2][]

相对应的配置：![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcnJ5cHR0ZXI_size_16_color_FFFFFF_t_70 3][]

运行的时候是点击idea右侧Maven projects：

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2hhcnJ5cHR0ZXI_size_16_color_FFFFFF_t_70 4][]

因为主要为了知道IOC的流程，所以用debug模式跑比较好。

[https_github.com_harrypitter_CreateSpring.git]: https://github.com/harrypitter/CreateSpring.git
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