diff --git a/src/main/java/org/checkerframework/specimin/TargetMethodFinderVisitor.java b/src/main/java/org/checkerframework/specimin/TargetMethodFinderVisitor.java
index 24558146..79d87012 100644
--- a/src/main/java/org/checkerframework/specimin/TargetMethodFinderVisitor.java
+++ b/src/main/java/org/checkerframework/specimin/TargetMethodFinderVisitor.java
@@ -12,8 +12,11 @@
 import com.github.javaparser.ast.expr.NameExpr;
 import com.github.javaparser.ast.expr.ObjectCreationExpr;
 import com.github.javaparser.ast.expr.SuperExpr;
+import com.github.javaparser.ast.stmt.CatchClause;
 import com.github.javaparser.ast.stmt.ExplicitConstructorInvocationStmt;
+import com.github.javaparser.ast.type.ReferenceType;
 import com.github.javaparser.ast.type.Type;
+import com.github.javaparser.ast.type.UnionType;
 import com.github.javaparser.ast.visitor.ModifierVisitor;
 import com.github.javaparser.ast.visitor.Visitable;
 import com.github.javaparser.resolution.UnsolvedSymbolException;
@@ -220,19 +223,34 @@ public Visitable visit(MethodDeclaration method, Void p) {
   @Override
   public Visitable visit(Parameter para, Void p) {
     if (insideTargetMethod) {
-      ResolvedType paraType = para.resolve().getType();
-      if (paraType.isReferenceType()) {
-        String paraTypeFullName =
-            paraType.asReferenceType().getTypeDeclaration().get().getQualifiedName();
-        usedClass.add(paraTypeFullName);
-        for (ResolvedType typeParameterValue : paraType.asReferenceType().typeParametersValues()) {
-          String typeParameterValueName = typeParameterValue.describe();
-          if (typeParameterValueName.contains("<")) {
-            // removing the "<...>" part if there is any.
-            typeParameterValueName =
-                typeParameterValueName.substring(0, typeParameterValueName.indexOf("<"));
+      Type type = para.getType();
+      if (type.isUnionType()) {
+        resolveUnionType(type.asUnionType());
+      } else {
+        // Parameter resolution (para.resolve()) does not work in catch clause.
+        // However, resolution works on the type of the parameter.
+        // Bug report: https://github.com/javaparser/javaparser/issues/4240
+        ResolvedType paramType;
+        if (para.getParentNode().isPresent() && para.getParentNode().get() instanceof CatchClause) {
+          paramType = para.getType().resolve();
+        } else {
+          paramType = para.resolve().getType();
+        }
+
+        if (paramType.isReferenceType()) {
+          String paraTypeFullName =
+              paramType.asReferenceType().getTypeDeclaration().get().getQualifiedName();
+          usedClass.add(paraTypeFullName);
+          for (ResolvedType typeParameterValue :
+              paramType.asReferenceType().typeParametersValues()) {
+            String typeParameterValueName = typeParameterValue.describe();
+            if (typeParameterValueName.contains("<")) {
+              // removing the "<...>" part if there is any.
+              typeParameterValueName =
+                  typeParameterValueName.substring(0, typeParameterValueName.indexOf("<"));
+            }
+            usedClass.add(typeParameterValueName);
           }
-          usedClass.add(typeParameterValueName);
         }
       }
     }
@@ -310,4 +328,18 @@ public Visitable visit(NameExpr expr, Void p) {
     }
     return super.visit(expr, p);
   }
+
+  /**
+   * Resolves unionType parameters one by one and adds them in the usedClass set.
+   *
+   * @param type unionType parameter
+   */
+  private void resolveUnionType(UnionType type) {
+    for (ReferenceType param : type.getElements()) {
+      ResolvedType paramType = param.resolve();
+      String paraTypeFullName =
+          paramType.asReferenceType().getTypeDeclaration().get().getQualifiedName();
+      usedClass.add(paraTypeFullName);
+    }
+  }
 }
diff --git a/src/main/java/org/checkerframework/specimin/UnsolvedClass.java b/src/main/java/org/checkerframework/specimin/UnsolvedClass.java
index e29b63a1..e9df67ea 100644
--- a/src/main/java/org/checkerframework/specimin/UnsolvedClass.java
+++ b/src/main/java/org/checkerframework/specimin/UnsolvedClass.java
@@ -37,6 +37,9 @@ public class UnsolvedClass {
   /** This field records the number of type variables for this class */
   private int numberOfTypeVariables = 0;
 
+  /** This field records if the class is a custom exception */
+  private boolean isExceptionType = false;
+
   /**
    * Create an instance of UnsolvedClass
    *
@@ -44,10 +47,23 @@ public class UnsolvedClass {
    * @param packageName the name of the package
    */
   public UnsolvedClass(@ClassGetSimpleName String className, String packageName) {
+    this(className, packageName, false);
+  }
+
+  /**
+   * Create an instance of UnsolvedClass
+   *
+   * @param className the name of the class
+   * @param packageName the name of the package
+   * @param isException does the class represents an exception?
+   */
+  public UnsolvedClass(
+      @ClassGetSimpleName String className, String packageName, boolean isException) {
     this.className = className;
     this.methods = new LinkedHashSet<>();
     this.packageName = packageName;
     this.classFields = new LinkedHashSet<>();
+    this.isExceptionType = isException;
   }
 
   /**
@@ -105,7 +121,11 @@ public void addFields(String variableExpression) {
     this.classFields.add(variableExpression);
   }
 
-  /** This method sets the number of type variables for the current class */
+  /**
+   * This method sets the number of type variables for the current class
+   *
+   * @param numberOfTypeVariables number of type variable in this class.
+   */
   public void setNumberOfTypeVariables(int numberOfTypeVariables) {
     this.numberOfTypeVariables = numberOfTypeVariables;
   }
@@ -172,7 +192,11 @@ public void updateFieldByType(String currentType, String correctType) {
   public String toString() {
     StringBuilder sb = new StringBuilder();
     sb.append("package ").append(packageName).append(";\n");
-    sb.append("public class ").append(className).append(getTypeVariablesAsString()).append(" {\n");
+    sb.append("public class ").append(className).append(getTypeVariablesAsString());
+    if (isExceptionType) {
+      sb.append(" extends Exception");
+    }
+    sb.append(" {\n");
     for (String variableDeclarations : classFields) {
       sb.append("    " + "public " + variableDeclarations + ";\n");
     }
diff --git a/src/main/java/org/checkerframework/specimin/UnsolvedSymbolVisitor.java b/src/main/java/org/checkerframework/specimin/UnsolvedSymbolVisitor.java
index 64cef010..de903af8 100644
--- a/src/main/java/org/checkerframework/specimin/UnsolvedSymbolVisitor.java
+++ b/src/main/java/org/checkerframework/specimin/UnsolvedSymbolVisitor.java
@@ -31,6 +31,7 @@
 import com.github.javaparser.ast.type.ReferenceType;
 import com.github.javaparser.ast.type.Type;
 import com.github.javaparser.ast.type.TypeParameter;
+import com.github.javaparser.ast.type.UnionType;
 import com.github.javaparser.ast.visitor.ModifierVisitor;
 import com.github.javaparser.ast.visitor.Visitable;
 import com.github.javaparser.resolution.UnsolvedSymbolException;
@@ -57,6 +58,7 @@
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
+import org.checkerframework.checker.nullness.qual.NonNull;
 import org.checkerframework.checker.nullness.qual.Nullable;
 import org.checkerframework.checker.signature.qual.ClassGetSimpleName;
 import org.checkerframework.checker.signature.qual.DotSeparatedIdentifiers;
@@ -526,7 +528,7 @@ public Visitable visit(MethodDeclaration node, Void arg) {
       try {
         nodeType.resolve();
       } catch (UnsolvedSymbolException | UnsupportedOperationException e) {
-        updateUnsolvedClassWithClassName(nodeTypeSimpleForm);
+        updateUnsolvedClassWithClassName(nodeTypeSimpleForm, false);
       }
     }
 
@@ -655,24 +657,22 @@ public Visitable visit(ClassOrInterfaceType typeExpr, Void p) {
   @Override
   public Visitable visit(Parameter parameter, Void p) {
     try {
-      parameter.resolve();
+      if (parameter.getType() instanceof UnionType) {
+        resolveUnionType(parameter);
+      } else {
+        if (parameter.getParentNode().isPresent()
+            && parameter.getParentNode().get() instanceof CatchClause) {
+          parameter.getType().resolve();
+        } else {
+          parameter.resolve();
+        }
+      }
       return super.visit(parameter, p);
     }
     // If the parameter originates from a Java built-in library, such as java.io or java.lang,
     // an UnsupportedOperationException will be thrown instead.
     catch (UnsolvedSymbolException | UnsupportedOperationException e) {
-      String parameterInString = parameter.toString();
-      if (isAClassPath(parameterInString)) {
-        // parameterInString needs to be a fully-qualified name. As this parameter has a form of
-        // class path, we can say that it is a fully-qualified name
-        @SuppressWarnings("signature")
-        UnsolvedClass newClass = getSimpleSyntheticClassFromFullyQualifiedName(parameterInString);
-        updateMissingClass(newClass);
-      } else {
-        // since it is unsolved, it could not be a primitive type
-        @ClassGetSimpleName String className = parameter.getType().asClassOrInterfaceType().getName().asString();
-        updateUnsolvedClassWithClassName(className);
-      }
+      handleParameterResolveFailure(parameter);
     }
     gotException = true;
     return super.visit(parameter, p);
@@ -695,7 +695,7 @@ public Visitable visit(ObjectCreationExpr newExpr, Void p) {
     try {
       List<String> argumentsCreation = getArgumentsFromObjectCreation(newExpr);
       UnsolvedMethod creationMethod = new UnsolvedMethod("", type, argumentsCreation);
-      updateUnsolvedClassWithClassName(type, creationMethod);
+      updateUnsolvedClassWithClassName(type, false, creationMethod);
     } catch (Exception q) {
       // can not solve the parameters for this object creation in this current run
     }
@@ -705,6 +705,46 @@ public Visitable visit(ObjectCreationExpr newExpr, Void p) {
     return newExpr;
   }
 
+  /**
+   * @param parameter parameter from visitor method which is unsolvable.
+   */
+  private void handleParameterResolveFailure(@NonNull Parameter parameter) {
+    String parameterInString = parameter.toString();
+    if (isAClassPath(parameterInString)) {
+      // parameterInString needs to be a fully-qualified name. As this parameter has a form of
+      // class path, we can say that it is a fully-qualified name
+      @SuppressWarnings("signature")
+      UnsolvedClass newClass = getSimpleSyntheticClassFromFullyQualifiedName(parameterInString);
+      updateMissingClass(newClass);
+    } else {
+      // since it is unsolved, it could not be a primitive type
+      @ClassGetSimpleName String className = parameter.getType().asClassOrInterfaceType().getName().asString();
+      if (parameter.getParentNode().isPresent()
+          && parameter.getParentNode().get() instanceof CatchClause) {
+        updateUnsolvedClassWithClassName(className, true);
+      } else {
+        updateUnsolvedClassWithClassName(className, false);
+      }
+    }
+  }
+
+  /**
+   * Given the unionType parameter, this method will try resolving each element separately. If any
+   * of the element is unsolvable, an unsolved class instance will be created to generate synthetic
+   * class for the element.
+   *
+   * @param parameter unionType parameter from visitor class
+   */
+  private void resolveUnionType(@NonNull Parameter parameter) {
+    for (var param : parameter.getType().asUnionType().getElements()) {
+      try {
+        param.resolve();
+      } catch (UnsolvedSymbolException | UnsupportedOperationException e) {
+        handleParameterResolveFailure(parameter);
+      }
+    }
+  }
+
   /**
    * Given the variable type and the basic declaration of that variable (such as "int x", "boolean
    * y", "Car redTruck",...), this methods will add an initial value to that declaration of the
@@ -790,7 +830,7 @@ public void updateUnsolvedClassWithMethod(
       returnType = desiredReturnType;
     }
     UnsolvedMethod thisMethod = new UnsolvedMethod(methodName, returnType, listOfParameters);
-    UnsolvedClass missingClass = updateUnsolvedClassWithClassName(className, thisMethod);
+    UnsolvedClass missingClass = updateUnsolvedClassWithClassName(className, false, thisMethod);
     syntheticMethodAndClass.put(methodName, missingClass);
 
     // if the return type is not specified, a synthetic return type will be created. This part of
@@ -873,15 +913,18 @@ public void updateClassesFromJarSourcesForMethodCall(MethodCallExpr expr) {
    * @param nameOfClass the name of an unsolved class
    * @param unsolvedMethods unsolved methods to add to the class before updating this visitor's set
    *     missing classes (optional, may be omitted)
+   * @param isExceptionType if the class is of exceptionType
    * @return the newly-created UnsolvedClass method, for further processing. This output may be
    *     ignored.
    */
   public UnsolvedClass updateUnsolvedClassWithClassName(
-      @ClassGetSimpleName String nameOfClass, UnsolvedMethod... unsolvedMethods) {
+      @ClassGetSimpleName String nameOfClass,
+      boolean isExceptionType,
+      UnsolvedMethod... unsolvedMethods) {
     // if the name of the class is not present among import statements, we assume that this unsolved
     // class is in the same directory as the current class
     String packageName = classAndPackageMap.getOrDefault(nameOfClass, currentPackage);
-    UnsolvedClass result = new UnsolvedClass(nameOfClass, packageName);
+    UnsolvedClass result = new UnsolvedClass(nameOfClass, packageName, isExceptionType);
     for (UnsolvedMethod unsolvedMethod : unsolvedMethods) {
       result.addMethod(unsolvedMethod);
     }
diff --git a/src/test/java/org/checkerframework/specimin/CustomExceptionTest.java b/src/test/java/org/checkerframework/specimin/CustomExceptionTest.java
new file mode 100644
index 00000000..558c2368
--- /dev/null
+++ b/src/test/java/org/checkerframework/specimin/CustomExceptionTest.java
@@ -0,0 +1,14 @@
+package org.checkerframework.specimin;
+
+import java.io.IOException;
+import org.junit.Test;
+
+public class CustomExceptionTest {
+  @Test
+  public void runTest() throws IOException {
+    SpeciminTestExecutor.runTestWithoutJarPaths(
+        "customexception",
+        new String[] {"com/example/Simple.java"},
+        new String[] {"com.example.Simple#test()"});
+  }
+}
diff --git a/src/test/java/org/checkerframework/specimin/Issue38Test.java b/src/test/java/org/checkerframework/specimin/Issue38Test.java
new file mode 100644
index 00000000..ecbed004
--- /dev/null
+++ b/src/test/java/org/checkerframework/specimin/Issue38Test.java
@@ -0,0 +1,15 @@
+package org.checkerframework.specimin;
+
+import java.io.IOException;
+import org.junit.Test;
+
+/** This test checks if Specimin will work for Union types */
+public class Issue38Test {
+  @Test
+  public void runTest() throws IOException {
+    SpeciminTestExecutor.runTestWithoutJarPaths(
+        "issue38",
+        new String[] {"com/example/Issue38.java"},
+        new String[] {"com.example.Issue38#test()"});
+  }
+}
diff --git a/src/test/java/org/checkerframework/specimin/NestedCatchClauseTest.java b/src/test/java/org/checkerframework/specimin/NestedCatchClauseTest.java
new file mode 100644
index 00000000..b1dec9fe
--- /dev/null
+++ b/src/test/java/org/checkerframework/specimin/NestedCatchClauseTest.java
@@ -0,0 +1,14 @@
+package org.checkerframework.specimin;
+
+import java.io.IOException;
+import org.junit.Test;
+
+public class NestedCatchClauseTest {
+  @Test
+  public void runTest() throws IOException {
+    SpeciminTestExecutor.runTestWithoutJarPaths(
+        "nestedcatchclause",
+        new String[] {"com/example/Simple.java"},
+        new String[] {"com.example.Simple#test()"});
+  }
+}
diff --git a/src/test/java/org/checkerframework/specimin/UnsolvableExceptionTest.java b/src/test/java/org/checkerframework/specimin/UnsolvableExceptionTest.java
new file mode 100644
index 00000000..bc3a6cfe
--- /dev/null
+++ b/src/test/java/org/checkerframework/specimin/UnsolvableExceptionTest.java
@@ -0,0 +1,14 @@
+package org.checkerframework.specimin;
+
+import java.io.IOException;
+import org.junit.Test;
+
+public class UnsolvableExceptionTest {
+  @Test
+  public void runTest() throws IOException {
+    SpeciminTestExecutor.runTestWithoutJarPaths(
+        "unsolvedexception",
+        new String[] {"com/example/Simple.java"},
+        new String[] {"com.example.Simple#test()"});
+  }
+}
diff --git a/src/test/resources/customexception/expected/com/example/CustomException.java b/src/test/resources/customexception/expected/com/example/CustomException.java
new file mode 100644
index 00000000..c3625957
--- /dev/null
+++ b/src/test/resources/customexception/expected/com/example/CustomException.java
@@ -0,0 +1,8 @@
+package com.example;
+
+public class CustomException extends Exception {
+
+    public CustomException(String msg) {
+        throw new Error();
+    }
+}
diff --git a/src/test/resources/customexception/expected/com/example/Simple.java b/src/test/resources/customexception/expected/com/example/Simple.java
new file mode 100644
index 00000000..218d41e0
--- /dev/null
+++ b/src/test/resources/customexception/expected/com/example/Simple.java
@@ -0,0 +1,12 @@
+package com.example;
+
+public class Simple {
+
+    public void test() {
+        try {
+            throw new CustomException("dummy");
+        } catch (CustomException e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/src/test/resources/customexception/input/com/example/CustomException.java b/src/test/resources/customexception/input/com/example/CustomException.java
new file mode 100644
index 00000000..a0fcf0e3
--- /dev/null
+++ b/src/test/resources/customexception/input/com/example/CustomException.java
@@ -0,0 +1,5 @@
+package com.example;
+public class CustomException extends Exception {
+    public CustomException (String msg) {
+    }
+}
diff --git a/src/test/resources/customexception/input/com/example/Simple.java b/src/test/resources/customexception/input/com/example/Simple.java
new file mode 100644
index 00000000..db4b6f40
--- /dev/null
+++ b/src/test/resources/customexception/input/com/example/Simple.java
@@ -0,0 +1,14 @@
+package com.example;
+
+import org.checkerframework.specimin.CustomExceptionTest;
+
+public class Simple {
+
+    public void test() {
+        try {
+            throw new CustomException("dummy");
+        } catch (CustomException e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/src/test/resources/issue38/expected/com/example/Issue38.java b/src/test/resources/issue38/expected/com/example/Issue38.java
new file mode 100644
index 00000000..edd3b42a
--- /dev/null
+++ b/src/test/resources/issue38/expected/com/example/Issue38.java
@@ -0,0 +1,16 @@
+package com.example;
+
+public class Issue38 {
+
+    static class ExampleClass {
+    }
+
+    public void test() {
+        try {
+            Class<?> exampleClass = ExampleClass.class;
+            ExampleClass instance = (ExampleClass) exampleClass.newInstance();
+        } catch (InstantiationException | IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/src/test/resources/issue38/input/com/example/Issue38.java b/src/test/resources/issue38/input/com/example/Issue38.java
new file mode 100644
index 00000000..9b4b2592
--- /dev/null
+++ b/src/test/resources/issue38/input/com/example/Issue38.java
@@ -0,0 +1,20 @@
+package com.example;
+
+public class Issue38 {
+
+    static class ExampleClass {
+        public ExampleClass(int value) {
+            // Constructor with a parameter
+        }
+    }
+
+    public void test() {
+        try {
+            // Attempting to create an instance of ExampleClass, which has no default constructor
+            Class<?> exampleClass = ExampleClass.class;
+            ExampleClass instance = (ExampleClass) exampleClass.newInstance();
+        } catch (InstantiationException | IllegalAccessException e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/src/test/resources/nestedcatchclause/expected/com/example/CustomException.java b/src/test/resources/nestedcatchclause/expected/com/example/CustomException.java
new file mode 100644
index 00000000..c3625957
--- /dev/null
+++ b/src/test/resources/nestedcatchclause/expected/com/example/CustomException.java
@@ -0,0 +1,8 @@
+package com.example;
+
+public class CustomException extends Exception {
+
+    public CustomException(String msg) {
+        throw new Error();
+    }
+}
diff --git a/src/test/resources/nestedcatchclause/expected/com/example/Simple.java b/src/test/resources/nestedcatchclause/expected/com/example/Simple.java
new file mode 100644
index 00000000..8c3fa9b7
--- /dev/null
+++ b/src/test/resources/nestedcatchclause/expected/com/example/Simple.java
@@ -0,0 +1,20 @@
+package com.example;
+
+public class Simple {
+
+    public void test() {
+        try {
+            throw new CustomException("dummy");
+        } catch (CustomException e) {
+            System.out.println("Caught custom exception: " + e.getMessage());
+            if (e.getMessage().contains("occurred")) {
+                System.out.println("Exception message indicates an occurrence.");
+            }
+            handleException(e);
+        }
+    }
+
+    private void handleException(CustomException e) {
+        throw new Error();
+    }
+}
\ No newline at end of file
diff --git a/src/test/resources/nestedcatchclause/input/com/example/CustomException.java b/src/test/resources/nestedcatchclause/input/com/example/CustomException.java
new file mode 100644
index 00000000..a0fcf0e3
--- /dev/null
+++ b/src/test/resources/nestedcatchclause/input/com/example/CustomException.java
@@ -0,0 +1,5 @@
+package com.example;
+public class CustomException extends Exception {
+    public CustomException (String msg) {
+    }
+}
diff --git a/src/test/resources/nestedcatchclause/input/com/example/Simple.java b/src/test/resources/nestedcatchclause/input/com/example/Simple.java
new file mode 100644
index 00000000..5ba101d2
--- /dev/null
+++ b/src/test/resources/nestedcatchclause/input/com/example/Simple.java
@@ -0,0 +1,21 @@
+package com.example;
+
+import org.checkerframework.specimin.CustomExceptionTest;
+
+public class Simple {
+
+    public void test() {
+        try {
+            throw new CustomException("dummy");
+        } catch (CustomException e) {
+            System.out.println("Caught custom exception: " + e.getMessage());
+            if (e.getMessage().contains("occurred")) {
+                System.out.println("Exception message indicates an occurrence.");
+            }
+            handleException(e);
+        }
+    }
+    private void handleException(CustomException e) {
+        System.out.println("Handling the exception: " + e.getMessage());
+    }
+}
diff --git a/src/test/resources/unsolvedexception/expected/com/example/CustomException.java b/src/test/resources/unsolvedexception/expected/com/example/CustomException.java
new file mode 100644
index 00000000..2cc3692c
--- /dev/null
+++ b/src/test/resources/unsolvedexception/expected/com/example/CustomException.java
@@ -0,0 +1,8 @@
+package com.example;
+
+public class CustomException extends Exception {
+
+    public CustomException(java.lang.String parameter0) {
+        throw new Error();
+    }
+}
\ No newline at end of file
diff --git a/src/test/resources/unsolvedexception/expected/com/example/Simple.java b/src/test/resources/unsolvedexception/expected/com/example/Simple.java
new file mode 100644
index 00000000..8131e25f
--- /dev/null
+++ b/src/test/resources/unsolvedexception/expected/com/example/Simple.java
@@ -0,0 +1,12 @@
+package com.example;
+
+public class Simple {
+
+    public void test() {
+        try {
+            throw new CustomException("It's an unsolvable custom exception");
+        } catch (CustomException e) {
+            e.printStackTrace();
+        }
+    }
+}
diff --git a/src/test/resources/unsolvedexception/input/com/example/Simple.java b/src/test/resources/unsolvedexception/input/com/example/Simple.java
new file mode 100644
index 00000000..46e51ef4
--- /dev/null
+++ b/src/test/resources/unsolvedexception/input/com/example/Simple.java
@@ -0,0 +1,13 @@
+package com.example;
+
+import org.checkerframework.specimin.CustomExceptionTest;
+
+public class Simple {
+    public void test() {
+        try {
+            throw new CustomException("It's an unsolvable custom exception");
+        } catch (CustomException e) {
+            e.printStackTrace();
+        }
+    }
+}
\ No newline at end of file