Java – conditionally inject beans

I want to inject a bean based on the string parameter passed from the client

public interface Report {
    generateFile();
}

public class ExcelReport extends Report {
    //implementation for generateFile
}

public class CSVReport extends Report {
    //implementation for generateFile
}

class MyController{
    Report report;
    public HttpResponse getReport() {
    }
}

I want to inject report instances based on the parameters passed Any help would be very useful Thank you in advance

Solution

Use factory method mode:

public enum ReportType {EXCEL,CSV};

@Service
public class ReportFactory {

    @Resource
    private ExcelReport excelReport;

    @Resource
    private CSVReport csvReport

    public Report forType(ReportType type) {
        switch(type) {
            case EXCEL: return excelReport;
            case CSV: return csvReport;
            default:
                throw new IllegalArgumentException(type);
        }
    }
}

When you use? Type = when CSV calls the controller, spring can create an enumeration of report types:

class MyController{

    @Resource
    private ReportFactory reportFactory;

    public HttpResponse getReport(@RequestParam("type") ReportType type){
        reportFactory.forType(type);
    }

}

However, reportfactory is very clumsy and needs to be modified every time a new report type is added If the list of report types is fixed, there is no problem But if you plan to add more and more types, this is a more powerful implementation:

public interface Report {
    void generateFile();
    boolean supports(ReportType type);
}

public class ExcelReport extends Report {
    publiv boolean support(ReportType type) {
        return type == ReportType.EXCEL;
    }
    //...
}

@Service
public class ReportFactory {

    @Resource
    private List<Report> reports;

    public Report forType(ReportType type) {
        for(Report report: reports) {
            if(report.supports(type)) {
                return report;
            }
        }
        throw new IllegalArgumentException("Unsupported type: " + type);
    }
}

With this implementation, adding a new report type is as simple as adding a new bean to implement report and a new reporttype enumeration value You can leave without enumerating and using strings (maybe even bean names), but I find strong typing useful

Finally, I thought: the name of the report is a little unfortunate Report class representation (stateless?) The encapsulation of some logic (strategy pattern), and the name indicates that it encapsulates values (data) I'll suggest report generator and so on