300行代碼手寫Spring核心--Spring初探
目標:我們通過查看源碼的方式一步步嘗試完成springIOC容器的初始化 並完成dispatchServlet的功能
1.首先創建一個我們自己的Servlet並繼承HttpServlet並重寫init方法
public class EVServlet extends HttpServlet {
@Override
public void init(ServletConfig config) throws ServletException {
super.init();
}
}
這一步和我們當初用servlet寫web項目是一樣的調用父類的init方法,我們這裏顯示地調用了父類的init無參方法,其實正常的servlet初始化是容器是調用含參init方法並在方法內部調用this.init(),並且this.config=config的,代碼:
public void init(ServletConfig config) throws ServletException {
this.config = config;
this.init();
}
public void init() throws ServletException {
}
所以我們正常在重寫父類的init含參方法時需要在一開始顯示地調用父類的有參init方法,這樣給 成員變量config賦了初值,在doget方法等內部隨後纔會獲取,但是在我們這裏只需要加載一次配置文件的類路徑,後續不再需要,就不再顯示地調用了
想一想spring當初完成dispatchServlet都是通過註解完成的,那麼我們就要自己完成當初spring配置好的註解,並在初始化的時候把加了註解的類讀取到內存然後並解析
2.我們創建自己的註解
(1)EVController
import java.lang.annotation.*;
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EVController {
}
(2)EVRequestMapping
import java.lang.annotation.*;
@Target({ElementType.TYPE,ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EVRequestMapping {
String value() default "";
}
(3)EVAutowired
import java.lang.annotation.*;
@Target({ElementType.FIELD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EVAutowired {
String value() default "";
}
(4)EVRequestParam
import java.lang.annotation.*;
@Target({ElementType.PARAMETER})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EVRequestParam {
String value() default "";
}
(5)EVService
@Target({ElementType.TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface EVService {
String value() default "";
}
3.我們的容器初始化需要那幾個步驟呢?
@Override
public void init(ServletConfig config) throws ServletException {
//1.加載配置文件
doLoadConfig(config.getInitParameter("contextConfigLocation"));
//2.掃描相關的類
doScanner(contextConfig.getProperty("scanPackage"));
//3.始化掃描到的類,並且將它們放入到IOC容器之中
doInstance();
//4.完成依賴注入
doAutowired();
//5、初始化HandlerMapping
initHandlerMapping();
System.out.println("EV Spring framework is init.");
super.init();
}
分爲五步,先根據我們配置文件定義的類掃描路徑掃描包下帶註解的類,放入IOC容器之中,然後完成依賴注入,並初始化HandlerMapping
4.配置文件
(1)web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:javaee="http://java.sun.com/xml/ns/javaee"
xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"
version="2.4">
<display-name>Evan Web Application</display-name>
<servlet>
<servlet-name>evmvc</servlet-name>
<servlet-class>v2.servlet.EVServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>application.properties</param-value>
</init-param>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>evmvc</servlet-name>
<url-pattern>/*</url-pattern>
</servlet-mapping>
</web-app>
(2)application.properties(就是初始化讀取的那個配置文件)
因爲只需要個類掃描路徑,就是一句話
scanPackage=demo//我們一會兒在項目路徑下創建個demo包,並把測試類寫在下面
5.骨架搭建好開始填充內容
(0)先創建一些變量
//保存application.properties配置文件中的內容
private Properties contextConfig = new Properties();
//保存掃描的所有的類名
private List<String> classNames = new ArrayList<String>();
//傳說中的IOC容器,我們來揭開它的神祕面紗
//爲了簡化程序,暫時不考慮ConcurrentHashMap
// 主要還是關注設計思想和原理
private Map<String,Object> ioc = new HashMap<String,Object>();
//保存url和Method的對應關係
// private Map<String,Method> handlerMapping = new HashMap<String,Method>();
//思考:爲什麼不用Map
//你用Map的話,key,只能是url
//Handler 本身的功能就是把url和method對應關係,已經具備了Map的功能
//根據設計原則:冗餘的感覺了,單一職責,最少知道原則,幫助我們更好的理解
private List<Handler> handlerMapping = new ArrayList<Handler>();
(1)填充doLoadConfig方法
private void doLoadConfig(String contextConfigLocation) {
//直接從類路徑下找到Spring主配置文件所在的路徑
//並且將其讀取出來放到Properties對象中
//相當於scanPackage=demo 從文件中保存到了內存中
InputStream fis = this.getClass().getClassLoader().getResourceAsStream(contextConfigLocation);
try {
//存放到Properties變量中
contextConfig.load(fis);
} catch (IOException e) {
e.printStackTrace();
} finally {
if (null != fis) {
try {
fis.close();
} catch (IOException e) {
e.printStackTrace();
}
}
}
}
ps:關於getResourceAsStream方法的作用請看我轉載的另一篇文章:https://blog.csdn.net/qq_38762479/article/details/89226107,總之是默認從ClassPath根下獲取資源,path不能以’/'開頭,最終是由ClassLoader獲取資源。
(2)填充doScanner方法
private void doScanner(String scanPackage) {
//把從配置文件中讀取到的值轉換爲文件路徑,實際上就是把.替換爲/就OK了。
//我們這裏路徑只有一個demo沒有.,但我們用的是properties文件如果路徑再多一層是有點的
//classpath
URL url = this.getClass().getClassLoader().getResource("/" + scanPackage.replaceAll("\\.", "/"));
File classPath = new File(url.getFile());
for (File file : classPath.listFiles()) {
//如果是文件夾,遞歸
if (file.isDirectory()) {
doScanner(scanPackage + "." + file.getName());
} else {
//因爲是類路徑所以都以.class結尾
if (!file.getName().endsWith(".class")) {
continue;
}
String className = (scanPackage + "." + file.getName().replace(".class", ""));
//存放掃描到的類名
classNames.add(className);
}
}
}
在url上打一個斷點給大家看一下:
大概就是這種效果了
(3)填充doInstance方法
private void doInstance() {
if (classNames.isEmpty()) {
return;
}
try {
for (String className : classNames) {
Class<?> clazz = Class.forName(className);
//什麼樣的類才需要初始化呢?
//加了註解的類,才初始化,怎麼判斷?
//爲了簡化代碼邏輯,主要體會設計思想,只舉例 @Controller和@Service,
// @Componment...就不一一舉例了
if (clazz.isAnnotationPresent(EVController.class)) {
Object instance = clazz.newInstance();
//Spring默認類名首字母小寫,方法寫在下面
String beanName = toLowerFirstCase(clazz.getSimpleName());
ioc.put(beanName, instance);
} else if (clazz.isAnnotationPresent(EVService.class)) {
//1、自定義的beanName
EVService service = clazz.getAnnotation(EVService.class);
String beanName = service.value();
//2、默認類名首字母小寫
if ("".equals(beanName.trim())) {
beanName = toLowerFirstCase(clazz.getSimpleName());
}
Object instance = clazz.newInstance();
ioc.put(beanName, instance);
//3、根據類型自動賦值,投機取巧的方式
for (Class<?> i : clazz.getInterfaces()) {
if (ioc.containsKey(i.getName())) {
throw new Exception("The “" + i.getName() + "” is exists!!");
}
//把接口的類型直接當成key了
ioc.put(i.getName(), instance);
}
} else {
continue;
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
//如果類名本身是小寫字母,確實會出問題
//但是我要說明的是:這個方法是我自己用,private的
//傳值也是自己傳,類也都遵循了駝峯命名法
//默認傳入的值,存在首字母小寫的情況,也不可能出現非字母的情況
//爲了簡化程序邏輯,就不做其他判斷了,大家瞭解就OK
//其實用寫註釋的時間都能夠把邏輯寫完了
private String toLowerFirstCase(String simpleName) {
char[] chars = simpleName.toCharArray();
//之所以加,是因爲大小寫字母的ASCII碼相差32,
// 而且大寫字母的ASCII碼要小於小寫字母的ASCII碼
//在Java中,對char做算學運算,實際上就是對ASCII碼做算學運算
chars[0] += 32;
return String.valueOf(chars);
}
(4)填充Autowired
private void doAutowired() {
if (ioc.isEmpty()) {
return;
}
for (Map.Entry<String, Object> entry : ioc.entrySet()) {
//Declared 所有的,特定的 字段,包括private/protected/default
//正常來說,普通的OOP編程只能拿到public的屬性
Field[] fields = entry.getValue().getClass().getDeclaredFields();
for (Field field : fields) {
if (!field.isAnnotationPresent(EVAutowired.class)) {
continue;
}
EVAutowired autowired = field.getAnnotation(EVAutowired.class);
//如果用戶沒有自定義beanName,默認就根據類型注入
//這個地方省去了對類名首字母小寫的情況的判斷
//小夥伴們自己去完善
String beanName = autowired.value().trim();
if ("".equals(beanName)) {
//獲得接口的類型,作爲key待會拿這個key到ioc容器中去取值
beanName = field.getType().getName();
}
//如果是public以外的修飾符,只要加了@Autowired註解,都要強制賦值
//反射中叫做暴力訪問, 強吻
field.setAccessible(true);
try {
//用反射機制,動態給字段賦值
field.set(entry.getValue(), ioc.get(beanName));
} catch (IllegalAccessException e) {
e.printStackTrace();
}
}
}
}
(5)填充initHandlerMapping
private void initHandlerMapping() {
if (ioc.isEmpty()) {
return;
}
for (Map.Entry<String, Object> entry : ioc.entrySet()) {
Class<?> clazz = entry.getValue().getClass();
if (!clazz.isAnnotationPresent(EVController.class)) {
continue;
}
//保存寫在類上面的@EVRequestMapping("/demo")
String baseUrl = "";
if (clazz.isAnnotationPresent(EVRequestMapping.class)) {
EVRequestMapping requestMapping = clazz.getAnnotation(EVRequestMapping.class);
baseUrl = requestMapping.value();
}
//默認獲取所有的public方法
for (Method method : clazz.getMethods()) {
if (!method.isAnnotationPresent(EVRequestMapping.class)) {
continue;
}
//方法上也可能有請求路徑
EVRequestMapping requestMapping = method.getAnnotation(EVRequestMapping.class);
//優化
// //demo///query
String regex = ("/" + baseUrl + "/" + requestMapping.value())
.replaceAll("/+", "/");
Pattern pattern = Pattern.compile(regex);
this.handlerMapping.add(new Handler(pattern, entry.getValue(), method));
// handlerMapping.put(url,method);
System.out.println("Mapped :" + pattern + "," + method);
}
}
}
//保存一個url和一個Method的關係
public class Handler {
//必須把url放到HandlerMapping纔好理解吧
private Pattern pattern; //正則
private Method method;
private Object controller;
private Class<?>[] paramTypes;
public Pattern getPattern() {
return pattern;
}
public Method getMethod() {
return method;
}
public Object getController() {
return controller;
}
public Class<?>[] getParamTypes() {
return paramTypes;
}
//形參列表
//參數的名字作爲key,參數的順序,位置作爲值
private Map<String, Integer> paramIndexMapping;
public Handler(Pattern pattern, Object controller, Method method) {
this.pattern = pattern;
this.method = method;
this.controller = controller;
paramTypes = method.getParameterTypes();
paramIndexMapping = new HashMap<String, Integer>();
putParamIndexMapping(method);
}
private void putParamIndexMapping(Method method) {
//提取方法中加了註解的參數
//把方法上的註解拿到,得到的是一個二維數組
//因爲一個參數可以有多個註解,而一個方法又有多個參數
Annotation[][] pa = method.getParameterAnnotations();
for (int i = 0; i < pa.length; i++) {
for (Annotation a : pa[i]) {
if (a instanceof EVRequestParam) {
String paramName = ((EVRequestParam) a).value();
if (!"".equals(paramName.trim())) {
paramIndexMapping.put(paramName, i);
}
}
}
}
//提取方法中的request和response參數
Class<?>[] paramsTypes = method.getParameterTypes();
for (int i = 0; i < paramsTypes.length; i++) {
Class<?> type = paramsTypes[i];
if (type == HttpServletRequest.class ||
type == HttpServletResponse.class) {
paramIndexMapping.put(type.getName(), i);
}
}
}
// private
}
這就完成容器的初始化
(6)dispatchServlet
然後要考慮如何把請求分發到我們已經儲存的HanderlerMapping
private void doDispatch(HttpServletRequest req, HttpServletResponse resp) throws Exception {
Handler handler = getHandler(req);
if (handler == null) {
// if(!this.handlerMapping.containsKey(url)){
resp.getWriter().write("404 Not Found!!!");
return;
}
//獲得方法的形參列表
Class<?>[] paramTypes = handler.getParamTypes();
Object[] paramValues = new Object[paramTypes.length];
Map<String, String[]> params = req.getParameterMap();
for (Map.Entry<String, String[]> parm : params.entrySet()) {
String value = Arrays.toString(parm.getValue()).replaceAll("\\[|\\]", "")
.replaceAll("\\s", ",");
if (!handler.paramIndexMapping.containsKey(parm.getKey())) {
continue;
}
int index = handler.paramIndexMapping.get(parm.getKey());
paramValues[index] = convert(paramTypes[index], value);
}
if (handler.paramIndexMapping.containsKey(HttpServletRequest.class.getName())) {
int reqIndex = handler.paramIndexMapping.get(HttpServletRequest.class.getName());
paramValues[reqIndex] = req;
}
if (handler.paramIndexMapping.containsKey(HttpServletResponse.class.getName())) {
int respIndex = handler.paramIndexMapping.get(HttpServletResponse.class.getName());
paramValues[respIndex] = resp;
}
Object returnValue = handler.method.invoke(handler.controller, paramValues);
if (returnValue == null || returnValue instanceof Void) {
return;
}
resp.getWriter().write(returnValue.toString());
}
private Handler getHandler(HttpServletRequest req) {
if (handlerMapping.isEmpty()) {
return null;
}
//絕對路徑
String url = req.getRequestURI();
//處理成相對路徑
String contextPath = req.getContextPath();
url = url.replaceAll(contextPath, "").replaceAll("/+", "/");
for (Handler handler : this.handlerMapping) {
Matcher matcher = handler.getPattern().matcher(url);
if (!matcher.matches()) {
continue;
}
return handler;
}
return null;
}
(7)重寫doGet和doPost方法
@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 {
//6、調用,運行階段
try {
doDispatch(req, resp);
} catch (Exception e) {
e.printStackTrace();
resp.getWriter().write("500 Exection,Detail : " + Arrays.toString(e.getStackTrace()));
}
}
(8)寫測試用例
1)接口
public interface IDemoService {
String get(String name);
}
2)實現Service
/**
* 核心業務邏輯
*/
@EVService
public class DemoService implements IDemoService {
public String get(String name) {
return "My name is " + name;
}
3)Controller
@EVController
@EVRequestMapping("/demo")
public class DemoAction {
@EVAutowired
private IDemoService demoService;
@EVRequestMapping("/query.*")
public void query(HttpServletRequest req, HttpServletResponse resp,
@EVRequestParam("name") String name){
// String result = demoService.get(name);
String result = "My name is " + name;
try {
resp.getWriter().write(result);
} catch (IOException e) {
e.printStackTrace();
}
}
@EVRequestMapping("/add")
public void add(HttpServletRequest req, HttpServletResponse resp,
@EVRequestParam("a") Integer a, @EVRequestParam("b") Integer b){
try {
resp.getWriter().write(a + "+" + b + "=" + (a + b));
} catch (IOException e) {
e.printStackTrace();
}
}
@EVRequestMapping("/sub")
public void add(HttpServletRequest req, HttpServletResponse resp,
@EVRequestParam("a") Double a, @EVRequestParam("b") Double b){
try {
resp.getWriter().write(a + "-" + b + "=" + (a - b));
} catch (IOException e) {
e.printStackTrace();
}
}
@EVRequestMapping("/remove")
public String remove(@EVRequestParam("id") Integer id){
return "" + id;
}
}
(9)運行結果截圖