[java]AvoidThrowingNullPointerException marks all NullPointerException objects as wrong, whether or not thrown (2580)

pmd-java/src/main/java/net/sourceforge/pmd/lang/java/rule/design/AvoidThrowingNullPointerExceptionRule.java

@@ -0,0 +1,77 @@
+/**
+ * BSD-style license; for more info see http://pmd.sourceforge.net/license.html
+ */
+
+package net.sourceforge.pmd.lang.java.rule.design;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import net.sourceforge.pmd.lang.java.ast.ASTAllocationExpression;
+import net.sourceforge.pmd.lang.java.ast.ASTClassOrInterfaceBody;
+import net.sourceforge.pmd.lang.java.ast.ASTClassOrInterfaceType;
+import net.sourceforge.pmd.lang.java.ast.ASTThrowStatement;
+import net.sourceforge.pmd.lang.java.ast.ASTVariableDeclarator;
+import net.sourceforge.pmd.lang.java.rule.AbstractJavaRule;
+
+/**
+ * Finds <code>throw</code> statements containing <code>NullPointerException</code>
+ * instances as thrown values
+ *
+ * @author <a href="mailto:michaeller.2012@gmail.com">Mykhailo Palahuta</a>
+ */
+public class AvoidThrowingNullPointerExceptionRule extends AbstractJavaRule {
+
+    @Override
+    public Object visit(ASTClassOrInterfaceBody node, Object data) {
+        if (bodyHasThrowNullPointerExceptionStatement(node)) {
+            addViolation(data, node);
+        }
+        return super.visit(node, data);
+    }
+
+    private boolean bodyHasThrowNullPointerExceptionStatement(ASTClassOrInterfaceBody body) {
+        List<ASTThrowStatement> throwStatements = body.findDescendantsOfType(ASTThrowStatement.class);
+        List<String> npeInstances = getNullPointerExceptionInstances(body);
+        for (ASTThrowStatement throwStatement : throwStatements) {
+            if (throwsNullPointerException(throwStatement, npeInstances)) {
+                return true;
+            }
+        }
+        return false;
+    }
+
+    private List<String> getNullPointerExceptionInstances(ASTClassOrInterfaceBody body) {
+        List<ASTAllocationExpression> allocations = body.findDescendantsOfType(ASTAllocationExpression.class);
+        List<String> npeInstances = new ArrayList<>();
+        for (ASTAllocationExpression allocation : allocations) {
+            if (allocatesNullPointerException(allocation)) {
+                String assignedVarName = getNameOfAssignedVariable(allocation);
+                npeInstances.add(assignedVarName);
+            }
+        }
+        return npeInstances;
+    }
+
+    private boolean allocatesNullPointerException(ASTAllocationExpression allocation) {
+        Class<?> allocatedType = getAllocatedInstanceType(allocation);
+        return allocatedType != null && NullPointerException.class.isAssignableFrom(allocatedType);
+    }
+
+    private Class<?> getAllocatedInstanceType(ASTAllocationExpression allocation) {
+        List<ASTClassOrInterfaceType> allocatedTypes = allocation
+                .findDescendantsOfType(ASTClassOrInterfaceType.class);
+        return allocatedTypes.isEmpty() ? null : allocatedTypes.get(0).getType();
+    }
+
+    private String getNameOfAssignedVariable(ASTAllocationExpression allocation) {
+        List<ASTVariableDeclarator> variableDeclarators = allocation.getParent()
+                .findDescendantsOfType(ASTVariableDeclarator.class);
+        return variableDeclarators.isEmpty() ? null : variableDeclarators.get(0).getName();
+    }
+
+    private boolean throwsNullPointerException(ASTThrowStatement throwStatement, List<String> npeInstances) {
+        String thrownImage = throwStatement.getFirstClassOrInterfaceTypeImage();
+        return "NullPointerException".equals(thrownImage) || npeInstances.contains(thrownImage);
+    }
+}

pmd-java/src/main/resources/category/java/design.xml

@@ -200,7 +200,7 @@ public void bar() {
           language="java"
           since="1.8"
           message="Avoid throwing null pointer exceptions."
-          class="net.sourceforge.pmd.lang.rule.XPathRule"
+          class="net.sourceforge.pmd.lang.java.rule.design.AvoidThrowingNullPointerExceptionRule"
           externalInfoUrl="${pmd.website.baseurl}/pmd_rules_java_design.html#avoidthrowingnullpointerexception">
         <description>
 <![CDATA[
@@ -234,16 +234,6 @@ public class Foo {
 ]]>
         </description>
         <priority>1</priority>
-        <properties>
-            <property name="version" value="2.0"/>
-            <property name="xpath">
-                <value>
-<![CDATA[
-//AllocationExpression/ClassOrInterfaceType[@Image='NullPointerException']
-]]>
-                </value>
-            </property>
-        </properties>
         <example>
 <![CDATA[
 public class Foo {

pmd-java/src/test/resources/net/sourceforge/pmd/lang/java/rule/design/xml/AvoidThrowingNullPointerException.xml

@@ -12,6 +12,32 @@ public class Foo {
     void bar() {
         throw new NullPointerException();
     }
+}
+        ]]></code>
+    </test-code>
+
+    <test-code>
+        <description>no problems if NullPointerException is only instantiated but not thrown</description>
+        <expected-problems>0</expected-problems>
+        <code><![CDATA[
+public class Foo {
+    void bar() {
+        Exception e = new NullPointerException("Test message");
+        String msg = e.getMessage();
+    }
+}
+        ]]></code>
+    </test-code>
+
+    <test-code>
+        <description>problem should be detected even if NullPointerException is stored in some intermediate variable</description>
+        <expected-problems>1</expected-problems>
+        <code><![CDATA[
+public class Foo {
+    void bar() {
+        Exception e = new NullPointerException();
+        throw e;
+    }
 }
         ]]></code>
     </test-code>