Jasper + JSF- java.lang.NullPointerException

I've simulated the same error in my environment by passing a wrong string from the .jasper file.

And when I did not compile the file .jrxml , then the file .jasper did not exist. And the reason a blank PDF page is generated is because the report is compiled ( .jasper ) by passing% empty%.

In the context of the question here: for whatever reason the parameter JRDataSource dataSource (of signature lista ) is being passed empty ([ " Guillaume - 2013 ]).

 JRBeanCollectionDataSource datasrc = new JRBeanCollectionDataSource(lista);

But I took the path as below:

String strJasper =  getServletContext()
       .getRealPath("/reports/stackoverflow_report.jasper");

System.out.println("strJasper = " + strJasper);

To simulate and test in my environment I did the following:

1) My database for the report:

CREATE SCHEMA 'stackoverflow' ;

CREATE TABLE 'Pages' (
  'id' int(10) unsigned NOT NULL AUTO_INCREMENT,
  'url' varchar(500) DEFAULT NULL,
  PRIMARY KEY ('id')
) ENGINE=InnoDB AUTO_INCREMENT=9 DEFAULT CHARSET=latin1;

INSERT INTO 'stackoverflow'.'Pages' ('url') 
VALUES ('https://pt.stackoverflow.com/questions/262662/inserir-valores-de-upload-num-array-com-outro-nome'),
        ('https://pt.stackoverflow.com/questions/579/por-que-n%C3%A3o-devemos-usar-fun%C3%A7%C3%B5es-do-tipo-mysql'),
        ('https://pt.stackoverflow.com/questions/262661/implementa%C3%A7%C3%A3o-do-jogo-mastermind'),
        ('https://pt.stackoverflow.com/questions/262653/erro-ao-importar-xls-para-o-postgres'),
        ('https://pt.stackoverflow.com/questions/262650/recuo-ap%C3%B3s-focus-em-input-com-jquery'),
        ('https://pt.stackoverflow.com/questions/262648/para-que-serve-o-seletor-media-no-css'),
        ('https://pt.stackoverflow.com/questions/262647/script-busca-python');

2) My file StackOverflowGenerateReport :

In the project structure the stackoverflow_report.jrxml files are in the folder: .jrxml .

<?xml version="1.0" encoding="UTF-8"?>
<jasperReport xmlns="http://jasperreports.sourceforge.net/jasperreports" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://jasperreports.sourceforge.net/jasperreports http://jasperreports.sourceforge.net/xsd/jasperreport.xsd" name="stackoverflow_report" pageWidth="595" pageHeight="842" columnWidth="555" leftMargin="20" rightMargin="20" topMargin="20" bottomMargin="20" >
    <property name="ireport.zoom" value="1.0"/>
    <property name="ireport.x" value="0"/>
    <property name="ireport.y" value="0"/>
    <parameter name="GENERATED_BY" class="java.lang.String">
        <defaultValueExpression><![CDATA["SEU NOME VEM AQUI"]]></defaultValueExpression>
    </parameter>
    <parameter name="PATH_IMG" class="java.lang.String">
        <defaultValueExpression><![CDATA["/path/to/WebContent/img"]]></defaultValueExpression>
    </parameter>
    <queryString>
        <![CDATA[SELECT
     Pages.'id',
     Pages.'url'
        FROM
     'stackoverflow_260791'.'Pages' Pages]]>
    </queryString>
    <field name="id" class="java.lang.Long">
        <fieldDescription><![CDATA[]]></fieldDescription>
    </field>
    <field name="url" class="java.lang.String">
        <fieldDescription><![CDATA[]]></fieldDescription>
    </field>
    <background>
        <band splitType="Stretch"/>
    </background>
    <pageHeader>
        <band height="94" splitType="Stretch">
            <textField pattern="EEEEE dd MMMMM yyyy">
                <reportElement x="364" y="57" width="188" height="14" />
                <textElement textAlignment="Right">
                    <font isBold="true"/>
                </textElement>
                <textFieldExpression class="java.util.Date" ><![CDATA[new java.util.Date()]]></textFieldExpression>
            </textField>
            <staticText>
                <reportElement x="182" y="19" width="346" height="27" />
                <textElement textAlignment="Center">
                    <font size="20" isBold="true"/>
                </textElement>
                <text><![CDATA[Stack Overflow | Relatório URLs]]></text>
            </staticText>
            <textField>
                <reportElement x="-1" y="71" width="553" height="18" />
                <textElement textAlignment="Right" verticalAlignment="Middle">
                    <font isBold="true"/>
                </textElement>
                <textFieldExpression><![CDATA["Gerado por  " + $P{GENERATED_BY}]]></textFieldExpression>
            </textField>
            <image scaleImage="FillFrame">
                <reportElement mode="Transparent" x="2" y="1" width="161" height="70" />
                <imageExpression><![CDATA[$P{PATH_IMG}+"/stackoverflow_logo.png"]]></imageExpression>
            </image>
        </band>
    </pageHeader>
    <columnHeader>
        <band height="25" splitType="Stretch">
            <staticText>
                <reportElement x="0" y="2" width="100" height="20" />
                <textElement textAlignment="Center" verticalAlignment="Middle">
                    <font size="12" isBold="true"/>
                </textElement>
                <text><![CDATA[ID]]></text>
            </staticText>
            <staticText>
                <reportElement x="100" y="2" width="100" height="20" />
                <textElement textAlignment="Left" verticalAlignment="Middle">
                    <font size="12" isBold="true"/>
                </textElement>
                <text><![CDATA[URL]]></text>
            </staticText>
            <line>
                <reportElement x="2" y="24" width="550" height="1" />
            </line>
        </band>
    </columnHeader>
    <detail>
        <band height="23" splitType="Stretch">
            <textField>
                <reportElement x="0" y="0" width="100" height="20" />
                <textElement textAlignment="Center" verticalAlignment="Middle">
                    <font size="10" isBold="false"/>
                </textElement>
                <textFieldExpression class="java.lang.Long" ><![CDATA[$F{id}]]></textFieldExpression>
            </textField>
            <textField isStretchWithOverflow="true">
                <reportElement x="100" y="0" width="455" height="20" />
                <textElement verticalAlignment="Middle"/>
                <textFieldExpression class="java.lang.String" ><![CDATA[$F{url}]]></textFieldExpression>
            </textField>
        </band>
    </detail>
    <pageFooter>
        <band height="36" splitType="Stretch"/>
    </pageFooter>
</jasperReport>

First we have to compile the file WebContent/reports/ using the .jasper library.

3) Example jasperreports.engine.JasperCompileManager :

public class StackOverflowGenerateReport
{
    Connection connection;
    private static final String strPathReportJrxml = "/WebContent/reports/stackoverflow_report.jrxml";
    private static final String dBName = "stackoverflow";
    private static final String pw = "sua_senha_mysql";

  public void generateReport()
  {
    try
    {
        HashMap<String, String> parameterMap = new HashMap<String, String>();
        parameterMap.put("GENERATED_BY", "Seu nome aqui");
        parameterMap.put("PATH_IMG", "/path/to/WebContent/img");

        Class.forName("com.mysql.jdbc.Driver");
        connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/"+dBName+"?user=root&password="+pw);

        String path = new File(".").getCanonicalPath() + strPathReportJrxml;
        System.out.println("Filling report...");
        String jasperReport = JasperCompileManager.compileReportToFile(path);

        System.out.println("jasperReport = " + jasperReport);
        JasperFillManager.fillReportToFile(
            jasperReport,
            parameterMap, 
            connection
        );
        System.out.println("Done!");
        connection.close();
    }
    catch (JRException e)
    {
      e.printStackTrace();
    }
    catch (ClassNotFoundException e)
    {
      e.printStackTrace();
    }
    catch (SQLException e)
    {
      e.printStackTrace();
    } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
    }
  }

  public static void main(String[] args)
  {
    new StackOverflowGenerateReport().generateReport();
  }

4) Creating a Java EE project. Edit the deployment descriptor , that is, edit the file: StackOverflowGenerateReport :

<servlet>
    <display-name>DbStackOverflowServlet</display-name>
    <servlet-name>DbStackOverflowServlet</servlet-name>
    <!-- <servlet-class>net.ensode.jasperbook.FirstReportSendToBrowserServlet</servlet-class> -->
    <servlet-class>net.ensode.jasperbook.DbStackOverflowServlet</servlet-class>
</servlet>
<servlet-mapping>
    <servlet-name>DbStackOverflowServlet</servlet-name>
    <url-pattern>/DbStackOverflowServlet</url-pattern>
</servlet-mapping>

5) The class WEB-INF/web.xml :

public class DbStackOverflowServlet extends HttpServlet {

     /**
     * 
     */
    private static final long serialVersionUID = 1L;
    private static final String strPathReportStream = "/reports/stackoverflow_report.jasper";
    private static final String dBName = "stackoverflow";
    private static final String pw = "senha_bando_mysql";

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        Connection connection;
        ServletOutputStream servletOutputStream = response.getOutputStream();
        InputStream reportStream = getServletConfig()
            .getServletContext()
            .getResourceAsStream(strPathReportStream);
        HashMap<String, String> parameterMap = new HashMap<String, String>();
        parameterMap.put("GENERATED_BY", "Seu nome aqui");
        parameterMap.put("PATH_IMG", "/PATH_DO_SEU_PROJETO_AQUI/WebContent/img");

        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/"+dBName+"?user=root&password="+pw);
            JasperRunManager.runReportToPdfStream(
                reportStream, 
                servletOutputStream,
                parameterMap, 
                connection
            );
            connection.close();
            servletOutputStream.flush();
            servletOutputStream.close();
        } catch (Exception e) {
            // display stack trace in the browser
            StringWriter stringWriter = new StringWriter();
            PrintWriter printWriter = new PrintWriter(stringWriter);
            e.printStackTrace(printWriter);
            response.setContentType("text/plain");
            response.getOutputStream().print(stringWriter.toString());
        }
    }
}

Accessing the link: DbStackOverflowServlet should have a result similar to the one shown below:

NOTE-1:Whengeneratingthehttp://localhost:8080/seu_projeto/DbStackOverflowServletfilefromiReport,thereweresomeerrorswhencompiling.jrxmlfromlibrary.jasper.SoIhadtoadaptthejasperreports.engine.JasperCompileManagerfile.Usethetemplateabove.

NOTE-2:Icouldnotrender.jrxmlcompiledbyiReportusing.jasperlibrarian.Then,discardthejasperreports.engine.JasperFillManagerofiReport.Use.jaspercompiledbyclass.jasperabove.Thereasondoesnotfithereinthecontextofthequestion.

Reference:

DavidR.Heffelfinger-2009],Copyright©2009PacktPublishing,# : Create, design, format, and export reports with the world's most popular Java reporting library. [ Gonçalves, Antonio - 2013 ], Apress, © 2013,
Juneau, Josh - 2013 ], Apress, © 2013, Java EE 7 Recipes : A Problem-Solution Approach - Proven Solutions for Java Enterprise Edition 7 Developement.
[ Michal Cmil et al - 2014 ), Copyright © 2014 Packt Publishing, Java EE 7 Development with WildFly : Leverage the power of the WildFly application server from JBoss to develop modern Java EE 7 applications. > [ SG Ganesh et al - 2015) , Apress; 2nd ed., OCP Java SE 8 Programmer : A Comprehensive OCPJP 8 Certification Guide. Accessed on: 12 Dec. 2017
[ Guillaume - 2013 ], Stack Overflow, Jasper creates empty PDF [duplicate] : Answer. Accessed on: 12 Dec. 2017.