Overview (Dependency Injection)

Posted on June 16, 2015 by nobukimi@gmail.com

DI (Dependency Injection) is one of key features in Spring framework beside (AOP). Spring is the framework that try to decouple the program in many way.

DI is one of ways to decouple the program like a Factory Pattern. In your code, you can GET RID OF “new” statement to create an object.

Example of Dependency:
In your code, the method A need object A1 in order to run it.

Example of Dependency Injection:
Your method A doesn’t have to create a object A1, instead, the object can be injected from somewhere else.

What is good about it?
Your method A can run it without object A1 that makes easier to test it.

There are three ways to do this in Spring framework:

Field Injection
Setter Injection
Constructor Injection

Dependency Injection: Setter Injection

Posted on June 4, 2015 by nobukimi@gmail.com

This is an example of Setter injection, which is most popular method compared to field and constructor injection. A business logic class uses a object of DAO service class.

This is annotation based DI, so you don’t need to specify a bean in XML file but you still need to tell annotation drive to servlet context.

<annotation-driven />
<context:component-scan base-package="com.ns.spring" />

As the line 20 to 24 shows, it will injects the dependency via a setter method. And 28 to 39 shows it usage.

package com.ns.spring.common;

import java.text.DecimalFormat;
import java.util.ArrayList;
import java.util.List;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

import com.ns.spring.constant.RtrnConstant;
import com.ns.spring.model.RMA_HDR;
import com.ns.spring.model.ui.RmaHdrModel;
import com.ns.spring.service.template.RmaHdrService;

@Component
public class RmaBL implements RtrnConstant {

	private static RmaHdrService hdrSvc;

	@Autowired(required = true)
	public void setHdrSvc(RmaHdrService hdrSvc) {
		this.hdrSvc = hdrSvc;
	}

	public static List<Object[]> getRmaHdrListObj(String rmaNum) {
		return hdrSvc.getListRmaHdrBySql(rmaNum);
	}

	public static RMA_HDR saveHdr(RmaHdrModel rma, HttpServletRequest req) {
		RMA_HDR obj = new RMA_HDR(rma);
		if (rma.getId() == 0) {
			hdrSvc.save(obj);
			// Set RMA# with formatted
			DecimalFormat df = new DecimalFormat("000000");
			obj.setRmaNum("RMA" + df.format((double) obj.getId()));
		}
		hdrSvc.update(obj);
		req.getSession().removeAttribute(CONST.HDR_LIST.getVal());
		return obj;
	}

	public static RMA_HDR getRmaHdrObj(String rmaNum) {
		List<Object[]> rmaHdrList = getRmaHdrListObj(rmaNum);
		if (!CommonBL.isEmpty(rmaHdrList)) {
			Object[] objArr = rmaHdrList.get(0);
			int id = (Integer) objArr[0];
			return hdrSvc.findById(id);
		}
		return null;
	}
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}

Dependency Injection: Field Injection

Posted on June 4, 2015 by nobukimi@gmail.com

This is a example of field injection, which is very simple. One controller use three different service classes to access data base (DAO service class).

This is annotation based DI, so you don’t need to specify a bean in XML file but you still need to tell annotation drive to servlet context.

<annotation-driven />
<context:component-scan base-package="com.ns.spring" />

Line 42 to 48 shows the field injection, and 65 to 94 use the object without “new” keyword.

package com.ns.spring;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import javax.servlet.http.HttpServletRequest;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.ResponseBody;
import org.springframework.web.servlet.ModelAndView;

import com.ns.spring.common.CommonBL;
import com.ns.spring.common.RmaBL;
import com.ns.spring.common.RsnBL;
import com.ns.spring.common.TpBL;
import com.ns.spring.common.TpRsnBL;
import com.ns.spring.common.gen.BLFactory;
import com.ns.spring.constant.RtrnConstant;
import com.ns.spring.model.RTRN_RSN;
import com.ns.spring.model.RTRN_TP;
import com.ns.spring.model.RTRN_TP_RSN_CMBN;
import com.ns.spring.model.ui.RmaHdrModel;
import com.ns.spring.model.ui.RtrnRsnModel;
import com.ns.spring.model.ui.RtrnTpModel;
import com.ns.spring.service.template.RtrnRsnService;
import com.ns.spring.service.template.RtrnTpRsnService;
import com.ns.spring.service.template.RtrnTpService;

@Controller
public class TpRsnController implements RtrnConstant {

	@Autowired(required = true)
	private RtrnTpService tpSvc;

	@Autowired(required = true)
	private RtrnRsnService rsnSvc;

	@Autowired(required = true)
	private RtrnTpRsnService tpRsnSvc;

	@RequestMapping(value = "/cUrlValAttrbMain01Jsp", params = "goToTpRsn", method = RequestMethod.POST)
	public ModelAndView goToTpRsn(ModelMap model, HttpServletRequest req) {
		return getMVSubTpRsn01(model, req);
	}

	@RequestMapping(value = "/cUrlValAttrbSubTpRsn01Jsp", params = "backToRmaFromTpRsn", method = RequestMethod.POST)
	public ModelAndView backToRmaFromTpRsn(Model model, HttpServletRequest req) {
		return getMVMain01(req);
	}

	@RequestMapping(value = "/cUrlValAttrbSubTpRsn01Jsp", params = "toBoundRsnList", method = RequestMethod.POST)
	public ModelAndView toBoundRsnList(@ModelAttribute("RtrnTpModel") RtrnTpModel tp, ModelMap model, HttpServletRequest req) {

		String tpSelected = (String) req.getSession().getAttribute(CONST.TP_SELECTED.getVal());
		if (CommonBL.hasValue(tpSelected)) {
			RTRN_TP tpObj = this.tpSvc.findById(tpSelected);
			if (tpObj != null) {
				List<String> selectedCheckBox = TpRsnBL.getRsnToBound(tp, req);
				if (!CommonBL.isEmpty(selectedCheckBox)) {
					Set<RTRN_RSN> rtrnRsns = new HashSet<RTRN_RSN>();
					for (String code : selectedCheckBox) {
						RTRN_RSN rsnObj = this.rsnSvc.findById(code);
						if (rsnObj != null) {
							rtrnRsns.add(rsnObj);
							tpObj.setRtrnRsns(rtrnRsns);
							this.tpSvc.saveOrUpdate(tpObj);
						}
					}
				}
			}
		}
		return getMVSubTpRsn01(model, req);
	}

	@RequestMapping(value = "/cUrlValAttrbSubTpRsn01Jsp", params = "toUnBoundRsnList", method = RequestMethod.POST)
	public ModelAndView toUnBoundRsnList(@ModelAttribute("RtrnTpModel") RtrnTpModel tp, ModelMap model, HttpServletRequest req) {

		String tpSelected = (String) req.getSession().getAttribute(CONST.TP_SELECTED.getVal());
		if (CommonBL.hasValue(tpSelected)) {
			List<String> selectedCheckBox = tp.getSelectedCheckBox();
			if (!CommonBL.isEmpty(selectedCheckBox)) {
				for (String code : selectedCheckBox) {
					RTRN_TP_RSN_CMBN tpRsnObj = this.tpRsnSvc.getTpRsnCmbnByHql(tpSelected, code);
					if (tpRsnObj != null) {
						this.tpRsnSvc.delete(tpRsnObj);
					}
				}
			}
		}
		return getMVSubTpRsn01(model, req);
	}

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}

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Tag Archives: DI

Overview (Dependency Injection)

Dependency Injection: Setter Injection

Dependency Injection: Field Injection