問題: 若今天有個@Autowired bean (此稱bean A)存在於某個Singleton bean (此稱bean B)中, 且bean A必須為prototype bean, 請問該如何實現此種配置呢?
思路: 這裡可以考慮以下情境, 假設有個singleton bean (bean B), 此bean的角色是個controller, 然後在bean B中注入一個bean A (@Autowired), 而我們希望每次有request進到這個controller的時候, 這個bean A都會是一個新的bean (即prototype bean).
以下先定義Request:
/**
* @author Carl Lu
*/
public class Request {
Long id;
String content;
public static Request getInstance(Long id, String content) {
Request request = new Request();
request.setId(id);
request.setContent(content);
return request;
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
}
再來是要被設定成prototype的bean A, 此處為validator:
import java.util.ArrayList;
import java.util.List;
import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;
import org.springframework.stereotype.Component;
/**
* @author Carl Lu
*/
@Component
@Scope(value = "prototype")
public class Validator {
private List<String> validationMessages = new ArrayList<>();
public Validator() {}
public List<String> validate(Request request) {
if (request.getContent() == null) {
validationMessages.add("Request: " + request.getId() + " failed (no content).");
}
return validationMessages;
}
}
然後是身為controller的singleton bean (bean B)
import java.util.List;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
/**
* @author Carl Lu
*/
@Component
public class RequestHandler {
@Autowired
private Validator validator;
public void handle(Request request) {
List<String> validationMsgs = validator.validate(request);
if (!validationMsgs.isEmpty()) {
validationMsgs.stream().forEach(msg -> System.out.println(msg));
} else {
System.out.println("Validation passed for request: " + request.getId());
}
System.out.println("Validator: " + validator.toString());
}
}
-> 就只是一個要處理request的class而已, 不過其中會注入bean A (prototype scope)
寫個test case來驗證看看:
import org.junit.Test;
import org.junit.runner.RunWith;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.test.SpringApplicationConfiguration;
import org.springframework.test.context.junit4.SpringJUnit4ClassRunner;
import com.rga.RgaCustomerModuleApplication;
/**
* @author Carl Lu
*/
@RunWith(SpringJUnit4ClassRunner.class)
@SpringApplicationConfiguration(classes = RgaCustomerModuleApplication.class)
public class RequestHandlerTest {
@Autowired
private RequestHandler requestHandler;
@Test
public void testPrototype() {
Request req1 = Request.getInstance(1l, "R1");
Request req2 = Request.getInstance(2l, "R2");
Request req3 = Request.getInstance(3l, null);
Request req4 = Request.getInstance(4l, "R4");
Request req5 = Request.getInstance(5l, null);
requestHandler.handle(req1);
requestHandler.handle(req2);
requestHandler.handle(req3);
requestHandler.handle(req4);
requestHandler.handle(req5);
}
}
所以現在來修改一下, 以下是改良過後的validator:
import java.util.ArrayList;
import java.util.List;
import org.springframework.context.annotation.Scope;
import org.springframework.context.annotation.ScopedProxyMode;
import org.springframework.stereotype.Component;
/**
* @author Carl Lu
*/
@Component
@Scope(proxyMode = ScopedProxyMode.TARGET_CLASS, value = "prototype")
public class Validator {
private List<String> validationMessages = new ArrayList<>();
public Validator() {}
public List<String> validate(Request request) {
if (request.getContent() == null) {
validationMessages.add("Request: " + request.getId() + " failed (no content).");
}
return validationMessages;
}
}
-> 我後來查了一些資料, 我想這個解法是我覺得比較好看的, 首先要include cglib, 這邊的原理是利用AOP scoped proxies在每次RequestHandler被呼叫的時候都注入一個新的validator bean
