迷你版Spring MVC 实现
项目建立
首先，建立一个空Maven项目，在java目录下，建立以下包结构。
.....
|--com.it
|-annotation
|-dao
|-service
|-web
DispatchServlet
接下来，引入servlet依赖
<dependency>
<groupId>javax.servlet</groupId>
<artifactId>javax.servlet-api</artifactId>
<version>3.1.0</version>
</dependency>
在annotation增加如下注解：
@Autowired.java
@Documented
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface Autowired {
String value();
}
@Controller.java
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Controller {
String value() default "";
}
@Repository.java
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Repository {
String value() default "";
}
@RequestMapping.java
@Documented
@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
public @interface RequestMapping {
String value();
}
@Service.java
@Documented
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface Service {
String value() default "";
}
编写核心Servlet
在Spring MVC中，DispatcherServlet是核心，因此我们也建立一个自己的DispatcherServlet来接收自己的请求。
DispatcherServlet.java
@WebServlet(urlPatterns = "/*", loadOnStartup = 0,
initParams = {@WebInitParam(name = "base-package", value = "com.it")})
public class DispatchServlet extends HttpServlet {
private static final String EMPTY = "";
/** 扫描的基础包*/
private String basePackage = EMPTY;
/** 扫描的基础包下面的类的全类名*/
private List<String> packagesName = new ArrayList<>();
/** key：注解里的值（默认为类名第一个字母小写） value ：类的实例化对象*/
private Map<String, Object> instanceMap = new HashMap<>();
/** key：类的全类名 value：注解里的值（默认为类名第一个字母小写）*/
private Map<String, String> nameMap = new HashMap<>();
/** key：请求路径 value： 所调用的方法*/
private Map<String, Method> urlMethodMap = new HashMap<>();
/** key：controller里的方法示例 value： 当前类的全类名*/
private Map<Method, String> methodPackageMap = new HashMap<>();
}
接下来，需要在serlvet初始化的时候，去扫描我们注解标识的类的信息，总体步骤如下：
1）扫描制定包下所有的类，进行初始化，记录类的全类名。
2）扫描所有标注@Controller/@Service/@Repository的注解类，并且记录全类名与实例的映射关系。
3）对于有@Autowired注解的字段，我们需要为其注入相应类的实例，为了方便，在这里统一用类的名称去获取，当然在spring 中可以通过类型等种种手段去注入。这里所有的类名默认转换成了 类名首字母小写的形式。
4）对于所有@RequestMapping注解的形式，需要将请求路径和相应的方法做关联记录，这样我们可以通过请求路径映射到我们的controller方法上。
Servlet初始化
@Override
public void init(ServletConfig config) throws ServletException {
basePackage = config.getInitParameter("base-package");
try {
scanBasePackage(basePackage);
instance(packagesName);
ioc();
handlerUrlMethod();
} catch (Exception e) {
e.printStackTrace();
System.out.println("框架加载失败");
}
}
第一步 ，包名扫描
private void scanBasePackage(String basePackage) {
Optional<URL> resource = Optional.ofNullable(this.getClass().getClassLoader().getResource(basePackage.replaceAll("\\.", "/")));
String path = resource.map(URL::getPath).orElse("");
File basePackageFile = new File(path);
Optional<File[]> files = Optional.ofNullable(basePackageFile.listFiles());
files.ifPresent(file -> {
for (File temp : file) {
if (temp.isDirectory()) {
scanBasePackage(basePackage + "." + temp.getName());
}
if (temp.isFile()) {
packagesName.add(basePackage + "." + temp.getName().split("\\.")[0]);
}
}
});
}
第二步，实例化类
private void instance(List<String> packagesNames) {
if (packagesNames.isEmpty()) {
return;
}
packagesNames.forEach(packageName -> {
try {
Class clazz = Class.forName(packageName);
String subName = clazz.getName().substring(clazz.getName().lastIndexOf(".")).replaceAll("\\.", EMPTY);
String clazzName = subName.substring(0, 1).toLowerCase() + subName.substring(1);
if (clazz.isAnnotationPresent(Controller.class)) {
Controller controller = (Controller) clazz.getAnnotation(Controller.class);
String controllerName = controller.value();
if (EMPTY.equals(controllerName)) {
controllerName = clazzName;
}
instanceMap.put(controllerName, clazz.newInstance());
nameMap.put(packageName, controllerName);
}
if (clazz.isAnnotationPresent(Service.class)) {
Service service = (Service) clazz.getAnnotation(Service.class);
String serviceName = service.value();
if (EMPTY.equals(serviceName)) {
serviceName = clazzName;
}
instanceMap.put(serviceName, clazz.newInstance());
nameMap.put(packageName, serviceName);
}
if (clazz.isAnnotationPresent(Repository.class)) {
Repository repository = (Repository) clazz.getAnnotation(Repository.class);
String respositoryName = repository.value();
if (EMPTY.equals(respositoryName)) {
respositoryName = clazzName;
}
instanceMap.put(respositoryName, clazz.newInstance());
nameMap.put(packageName, respositoryName);
}
} catch (Exception e) {
e.printStackTrace();
System.out.println("类加载失败");
}
});
}
第三步，注入类的实例
private void ioc() throws IllegalAccessException {
for (Map.Entry<String, Object> instance : instanceMap.entrySet()) {
Field[] declaredFields = instance.getValue().getClass().getDeclaredFields();
for (Field declaredField : declaredFields) {
if (declaredField.isAnnotationPresent(Autowired.class)) {
String value = declaredField.getAnnotation(Autowired.class).value();
declaredField.setAccessible(true);
declaredField.set(instance.getValue(), instanceMap.get(value));
}
}
}
}
第四步，处理请求路径与方法的映射
private void handlerUrlMethod() {
if (packagesName.isEmpty()) {
return;
}
packagesName.forEach(packageName -> {
try {
Class clazz = Class.forName(packageName);
if (clazz.isAnnotationPresent(Controller.class)) {
Method[] methods = clazz.getMethods();
StringBuffer baseUrl = new StringBuffer();
if (clazz.isAnnotationPresent(RequestMapping.class)) {
RequestMapping controllerClazzMapping = (RequestMapping) clazz.getAnnotation(RequestMapping.class);
baseUrl.append(controllerClazzMapping.value());
}
for (Method method : methods) {
if (method.isAnnotationPresent(RequestMapping.class)) {
RequestMapping methodMapping = method.getAnnotation(RequestMapping.class);
baseUrl.append(methodMapping.value());
urlMethodMap.put(baseUrl.toString(), method);
methodPackageMap.put(method, packageName);
}
}
}
} catch (Exception e) {
e.printStackTrace();
System.out.println("获取映射失败");
}
});
}
编写GET/POST方法
编写GET/POST方法，使请求映射到我们的Controller上
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doPost(req, resp);
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String uri = req.getRequestURI();
String contextPath = req.getContextPath();
String path = uri.replace(contextPath, EMPTY);
Optional<Method> method = Optional.ofNullable(urlMethodMap.get(path));
method.ifPresent(m -> {
String packageName = methodPackageMap.get(m);
String controllerName = nameMap.get(packageName);
Object controllerObj = instanceMap.get(controllerName);
m.setAccessible(true);
try {
m.invoke(controllerObj);
} catch (Exception e) {
e.printStackTrace();
}
});
}
编写测试
UserDao.java
@Repository
public class UserDao {
public void insert(){
System.out.println("insert user:");
}
}
UserService.java
@Service
public class UserService {
@Autowired("userDao")
private UserDao userDao;
public void insert() {
userDao.insert();
}
}
UserController.java
@Controller
@RequestMapping("/user")
public class UserController {
@Autowired("userService")
private UserService userService;
@RequestMapping("/insert")
public void insert() {
userService.insert();
}
}
编写完成后，在tomcat启动，访问 IP:PORT + /user/insert 后，可以在控制台看到 insert user:的输出，说明我们的迷你版Spring MVC可以正常工作啦。
代码参考：mymvc