Indexing order of Headers at annotations to write

src/main/java/io/github/millij/poi/ss/model/annotations/SheetColumn.java

@@ -26,6 +26,8 @@
      */
     String value() default "";
 
+    int index() default -1;
+
     /**
      * Setting this to <code>false</code> will enable the null check on the Column values, to ensure
      * non-null values for the field.

src/main/java/io/github/millij/poi/util/Spreadsheet.java

@@ -10,6 +10,7 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 
 import org.apache.commons.beanutils.BeanUtils;
 import org.apache.commons.lang3.StringUtils;
@@ -58,26 +59,28 @@ public static Map<String, String> getPropertyToColumnNameMap(Class<?> beanType)
         // Fields
         Field[] fields = beanType.getDeclaredFields();
         for (Field f : fields) {
-            String fieldName = f.getName();
-            mapping.put(fieldName, fieldName);
+            if (!f.isAnnotationPresent(SheetColumn.class)) {
+                continue;
+            }
 
+            final String fieldName = f.getName();
             SheetColumn ec = f.getAnnotation(SheetColumn.class);
-            if (ec != null && StringUtils.isNotEmpty(ec.value())) {
-                mapping.put(fieldName, ec.value());
+            if (ec != null) {
+                mapping.put(fieldName, StringUtils.isBlank(ec.value()) ? fieldName : ec.value());
             }
         }
 
         // Methods
         Method[] methods = beanType.getDeclaredMethods();
         for (Method m : methods) {
-            String fieldName = Beans.getFieldName(m);
-            if (!mapping.containsKey(fieldName)) {
-                mapping.put(fieldName, fieldName);
+            if (!m.isAnnotationPresent(SheetColumn.class)) {
+                continue;
             }
 
+            final String fieldName = Beans.getFieldName(m);
             SheetColumn ec = m.getAnnotation(SheetColumn.class);
-            if (ec != null && StringUtils.isNotEmpty(ec.value())) {
-                mapping.put(fieldName, ec.value());
+            if (ec != null) {
+                mapping.put(fieldName, StringUtils.isBlank(ec.value()) ? fieldName : ec.value());
             }
         }
 
@@ -103,12 +106,60 @@ public static List<String> getColumnNames(Class<?> beanType) {
         // Bean Property to Column Mapping
         final Map<String, String> propToColumnMap = getPropertyToColumnNameMap(beanType);
 
+        final Map<Integer, String> indexToPropMap = getIndexToPropertyMap(beanType);
+
+        if (propToColumnMap.size() == indexToPropMap.size()) {
+
+            final Set<Integer> indexSet = indexToPropMap.keySet();
+            List<Integer> indexList = new ArrayList<Integer>(indexSet);
+            Collections.sort(indexList);
+
+            List<String> indexedColumns = new ArrayList<String>();
+            for (Integer index : indexList) {
+                indexedColumns.add(propToColumnMap.get(indexToPropMap.get(index)));
+                if (index == -1) {
+                    LOGGER.info("Writing One field : '{}' at first column as no index specified",
+                            propToColumnMap.get(indexToPropMap.get(index)));
+                }
+            }
+            return indexedColumns;
+        }
+
+
+        LOGGER.info("Failed to write headers in partially indexed order. Proceeded to write in random order");
         final ArrayList<String> columnNames = new ArrayList<>(propToColumnMap.values());
         return columnNames;
     }
 
 
-
+    public static Map<Integer, String> getIndexToPropertyMap(Class<?> beanClz) {
+
+        Map<Integer, String> indexToPropMap = new HashMap<Integer, String>();
+
+        Field[] fields = beanClz.getDeclaredFields();
+        for (Field f : fields) {
+            if (!f.isAnnotationPresent(SheetColumn.class)) {
+                continue;
+            }
+            final String fieldName = f.getName();
+            SheetColumn ec = f.getDeclaredAnnotation(SheetColumn.class);
+            indexToPropMap.put(ec.index(), fieldName);
+        }
+
+        Method[] methods = beanClz.getDeclaredMethods();
+        for (Method m : methods) {
+            if (!m.isAnnotationPresent(SheetColumn.class)) {
+                continue;
+            }
+            final String fieldName = Beans.getFieldName(m);
+            SheetColumn ec = m.getDeclaredAnnotation(SheetColumn.class);
+            indexToPropMap.put(ec.index(), fieldName);
+        }
+
+        return indexToPropMap;
+    }
+
+
 
     // Read from Bean : as Row Data
     // ------------------------------------------------------------------------

src/test/java/io/github/millij/bean/EmployeeIndexed.java

@@ -0,0 +1,98 @@
+package io.github.millij.bean;
+
+import io.github.millij.poi.ss.model.annotations.Sheet;
+import io.github.millij.poi.ss.model.annotations.SheetColumn;
+
+
+@Sheet
+public class EmployeeIndexed {
+    private String id;
+    private String name;
+
+    @SheetColumn(value = "Age",index = 2)
+    private Integer age;
+
+    @SheetColumn(value = "Gender", index = 3)
+    private String gender;
+
+    @SheetColumn(value = "Height (mts)", index = 4)
+    private Double height;
+
+    @SheetColumn(value = "Address", index = 5)
+    private String address;
+
+
+    public EmployeeIndexed() {
+        // Default
+    }
+
+    public EmployeeIndexed(String id, String name, Integer age, String gender, Double height, String address) {
+        super();
+
+        this.id = id;
+        this.name = name;
+        this.age = age;
+        this.gender = gender;
+        this.height = height;
+        this.address = address;
+
+    }
+
+
+
+    @SheetColumn(value = "ID", index = 0)
+    public String getId() {
+        return id;
+    }
+
+    public void setId(String id) {
+        this.id = id;
+    }
+
+    @SheetColumn(value = "Name", index = 1)
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public Integer getAge() {
+        return age;
+    }
+
+    public void setAge(Integer age) {
+        this.age = age;
+    }
+
+    public String getGender() {
+        return gender;
+    }
+
+    public void setGender(String gender) {
+        this.gender = gender;
+    }
+
+    public Double getHeight() {
+        return height;
+    }
+
+    public void setHeight(Double height) {
+        this.height = height;
+    }
+
+    public String getAddress() {
+        return address;
+    }
+
+    public void setAddress(String address) {
+        this.address = address;
+    }
+
+    @Override
+    public String toString() {
+        return "Emp_indexed [id=" + id + ", name=" + name + ", age=" + age + ", gender=" + gender + ", height=" + height
+                + ", address=" + address + "]";
+    }
+}

src/test/java/io/github/millij/poi/ss/writer/IndexedHeadersWriterTest.java

@@ -0,0 +1,44 @@
+package io.github.millij.poi.ss.writer;
+
+import java.io.IOException;
+import java.util.ArrayList;
+import java.util.List;
+
+import org.junit.Test;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import io.github.millij.bean.Employee;
+import io.github.millij.bean.EmployeeIndexed;
+import io.github.millij.poi.ss.model.annotations.SheetColumn;
+import io.github.millij.poi.ss.writer.SpreadsheetWriter;
+import io.github.millij.poi.ss.writer.SpreadsheetWriterTest;
+
+
+public class IndexedHeadersWriterTest {
+    private static final Logger LOGGER = LoggerFactory.getLogger(SpreadsheetWriterTest.class);
+
+    private final String _path_test_output = "test-cases/output/";
+
+
+
+    @Test
+    public void test_write_xlsx_single_sheet() throws IOException {
+        final String filepath_output_file = _path_test_output.concat("indexed_header_writer_sample.xlsx");
+
+        // Excel Writer
+        LOGGER.info("test_write_xlsx_single_sheet :: Writing to file - {}", filepath_output_file);
+        SpreadsheetWriter gew = new SpreadsheetWriter(filepath_output_file);
+
+        // Employees
+        List<EmployeeIndexed> employees = new ArrayList<EmployeeIndexed>();
+        employees.add(new EmployeeIndexed("1", "foo", 12, "MALE", 1.68, "Chennai"));
+        employees.add(new EmployeeIndexed("2", "bar", 24, "MALE", 1.98, "Banglore"));
+        employees.add(new EmployeeIndexed("3", "foo bar", 10, "FEMALE", 2.0, "Kolkata"));
+
+        // Write
+        gew.addSheet(EmployeeIndexed.class, employees);
+        gew.write();
+    }
+
+}