[ch03] Calculator with Template/Callback.

src/main/java/ch03/springbook/calculator/Calculator.java

@@ -0,0 +1,68 @@
+package ch03.springbook.calculator;
+
+import java.io.BufferedReader;
+import java.io.FileReader;
+import java.io.IOException;
+
+public class Calculator {
+
+	public Integer calcSum(String filePath) throws IOException {
+
+		return lineReadTemplate(
+			filePath,
+			new LineCallBack() {
+				@Override
+				public Integer doSomethingWithLine(String line, Integer value) {
+					return value + Integer.valueOf(line);
+				}
+			},
+			0
+	   );
+	}
+
+	public Integer calcMultiply(String filePath) throws IOException {
+
+		return lineReadTemplate(
+			filePath,
+			new LineCallBack() {
+				@Override
+				public Integer doSomethingWithLine(String line, Integer value) {
+					return value * Integer.valueOf(line);
+				}
+			},
+			1
+	   );
+	}
+
+	public Integer lineReadTemplate(String filePath, LineCallBack lineCallBack, int initVal) throws IOException {
+
+		BufferedReader br = null;
+
+		try {
+
+			br = new BufferedReader(new FileReader(filePath));
+
+			Integer res = initVal;
+			String line = null;
+
+			while ((line = br.readLine()) != null) {
+				res = lineCallBack.doSomethingWithLine(line, res);
+			}
+
+			return res;
+
+		} catch (IOException e) {
+			throw e;
+
+		} finally {
+
+			if (br != null) {
+				try {
+					br.close();
+				} catch (IOException e) {
+					throw e;
+				}
+			}
+		}
+	}
+}

src/main/java/ch03/springbook/calculator/LineCallBack.java

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+package ch03.springbook.calculator;
+
+public interface LineCallBack {
+	Integer doSomethingWithLine(String line, Integer value);
+}

src/main/resources/numbers.txt

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+1
+2
+3
+4

src/test/java/ch03/springbook/calculator/CalcSumTest.java

@@ -0,0 +1,32 @@
+package ch03.springbook.calculator;
+
+import static org.hamcrest.CoreMatchers.is;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertThat;
+
+import java.io.IOException;
+
+import org.junit.Before;
+import org.junit.Test;
+
+public class CalcSumTest {
+
+	private Calculator calculator;
+	private String numFilePath;
+
+	@Before
+	public void setUp() {
+		this.calculator = new Calculator();
+		this.numFilePath = getClass().getResource("/numbers.txt").getPath();
+	}
+
+	@Test
+	public void sumOfNumbers() throws IOException {
+		assertThat(calculator.calcSum(numFilePath), is(10));
+	}
+
+	@Test
+	public void multiplyOfNumbers() throws IOException {
+		assertThat(calculator.calcMultiply(numFilePath), is(24));
+	}
+}