### CEL Java Hello World Example

Source: https://github.com/google/cel-java/blob/main/README.md

A basic Java example demonstrating how to compile and evaluate a CEL expression using CelCompiler and CelRuntime. It shows setting up the environment, compiling an expression, and evaluating it with input variables.

```java
import dev.cel.common.CelAbstractSyntaxTree;
import dev.cel.common.CelValidationException;
import dev.cel.common.types.SimpleType;
import dev.cel.compiler.CelCompiler;
import dev.cel.compiler.CelCompilerFactory;
import dev.cel.runtime.CelEvaluationException;
import dev.cel.runtime.CelRuntime;
import dev.cel.runtime.CelRuntimeFactory;
import java.util.Map;

public class HelloWorld {
  // Construct the compilation and runtime environments.
  // These instances are immutable and thus trivially thread-safe and amenable to caching.
  private static final CelCompiler CEL_COMPILER = 
      CelCompilerFactory.standardCelCompilerBuilder().addVar("my_var", SimpleType.STRING).build();
  private static final CelRuntime CEL_RUNTIME = 
      CelRuntimeFactory.standardCelRuntimeBuilder().build();

  public void run() throws CelValidationException, CelEvaluationException {
    // Compile the expression into an Abstract Syntax Tree.
    CelAbstractSyntaxTree ast = CEL_COMPILER.compile("my_var + '!'").getAst();

    // Plan an executable program instance.
    CelRuntime.Program program = CEL_RUNTIME.createProgram(ast);

    // Evaluate the program with an input variable.
    String result = (String) program.eval(Map.of("my_var", "Hello World"));
    System.out.println(result); // 'Hello World!'
  }
}
```

--------------------------------

### Bash - Verify Java and Bazel Installation

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Commands to verify that Java Development Kit (JDK) and Bazel are installed and accessible in the system's PATH. These tools are prerequisites for the CEL-Java codelab.

```bash
java --version
```

```bash
bazel
```

--------------------------------

### CelOptimizer Initialization

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Initializes the CelOptimizer with standard builders, including the compiler and runtime instances. This setup is necessary for performing AST optimizations.

```java
private static final CelOptimizer CEL_OPTIMIZER =
    CelOptimizerFactory.standardCelOptimizerBuilder(CEL_COMPILER, CEL_RUNTIME)
        .build();
```

--------------------------------

### Bash - Clone CEL-Java Repository and Run Tests

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Instructions for cloning the CEL-Java GitHub repository and running the initial set of tests for the codelab exercises. This setup step ensures the development environment is ready.

```bash
git clone git@github.com:google/cel-java.git
cd cel-java
```

```bash
bazel test //codelab/src/test/codelab:Exercise1Test --test_output=errors
```

--------------------------------

### Constructing AttributeContext.Request Proto

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Example of constructing a protobuf object `AttributeContext.Request` using a CEL expression. It demonstrates setting nested fields and using input variables like `jwt` and `now`. The example also shows how to set the expected output message for validation.

```java
import com.google.api.expr.v1alpha1.StructTypeReference;
import com.google.protobuf.Struct;
import com.google.protobuf.Value;
import com.google.rpc.context.AttributeContext;
import dev.cel.common.CelAbstractSyntaxTree;
import dev.cel.common.CelValidationException;
import dev.cel.compiler.CelCompiler;
import dev.cel.compiler.CelCompilerFactory;
import dev.cel.common.types.CelType;
import dev.cel.common.types.CelType.Message;
import dev.cel.common.types.CelType.Primitive;
import dev.cel.common.types.CelType.String;
import dev.cel.common.types.CelType.Null;
import dev.cel.common.types.CelType.Null.NullType;
import dev.cel.common.types.CelType.Any;
import dev.cel.common.types.CelType.List;
import dev.cel.common.types.CelType.Map;
import dev.cel.common.types.CelType.Function;
import dev.cel.common.types.CelType.Error;
import dev.cel.common.types.CelType.TypeParam;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.common.types.CelType.TypeParam.TypeParamKind.TypeParamKindEnum;
import dev.cel.
```

--------------------------------

### CEL Java Extensions Examples

Source: https://github.com/google/cel-java/blob/main/README.md

Illustrates the usage of various canonical extensions provided by CEL-Java for string manipulation, mathematical operations, Protocol Buffers, and local bindings.

```java
// String manipulation
'hello hello'.replace('he', 'we')     // returns 'wello wello'
'hello hello hello'.split(' ')     // returns ['hello', 'hello', 'hello']

// Math extensions
math.greatest(-42.0, -21.5, -100.0)   // -21.5
math.least(-42.0, -21.5, -100.0)   // -100.0

// Proto extensions
proto.getExt(msg, google.expr.proto2.test.int32_ext) // returns int value

// Local bindings
cel.bind(a, 'hello',
    cel.bind(b, 'world', a + b + b + a)) // "helloworldworldhello"
```

--------------------------------

### CEL Expression Examples

Source: https://github.com/google/cel-java/blob/main/README.md

Demonstrates the common syntax of CEL across Java, Go, and TypeScript for various checks like resource name prefixes, time window calculations, and list filtering.

```java
resource.name.startsWith("/groups/"+auth.claims.group)
```

```go
request.time - resource.age < duration("24h")
```

```typescript
auth.claims.email_verified && resources.all(r, r.startsWith(auth.claims.email))
```

--------------------------------

### CEL Java Environment Setup

Source: https://github.com/google/cel-java/blob/main/README.md

Illustrates two ways to set up the CEL environment in Java: a simple standard builder and a more common approach using separate CelCompilerFactory and CelRuntimeFactory for granular control over type-checking and runtime configurations.

```java
Cel cel = CelFactory.standardCelBuilder().build();
```

```java
// Example environment for the following expression:
//    resource.name.startsWith('/groups/' + group)
CelCompiler cel = CelCompilerFactory.standardCelCompilerBuilder()
    .setStandardMacros(CelStandardMacro.HAS)
    .setContainer("google.rpc.context.AttributeContext")
    .addMessageTypes(AttributeContext.getDescriptor())
    .addVar("resource",
        StructTypeReference.create("google.rpc.context.AttributeContext.Resource"))
    .addVar("group", SimpleType.STRING)
    .build();
```

--------------------------------

### Error Reporting Example

Source: https://github.com/google/cel-java/blob/main/README.md

Demonstrates how CEL provides friendly error messages with pointers to the exact location of issues in the source code.

```sh
ERROR: <input>:1:40: undefined field 'undefined'
    | TestAllTypes{single_int32: 1, undefined: 2}
    | .......................................^
```

--------------------------------

### CEL Environment Setup

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Sets up the standard CEL environment for expression compilation and evaluation in Java. It configures CelOptions and builds immutable CelCompiler and CelRuntime instances, which are thread-safe and can be cached.

```java
private static final CelOptions CEL_OPTIONS = CelOptions.current().build();

private static final CelCompiler CEL_COMPILER =
        CelCompilerFactory.standardCelCompilerBuilder()
             .setOptions(CEL_OPTIONS)
             .build();

private static final CelRuntime CEL_RUNTIME =
        CelRuntimeFactory.standardCelRuntimeBuilder()
             .setOptions(CEL_OPTIONS)
             .build();
```

--------------------------------

### Standard CEL Compiler and Runtime Setup

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Demonstrates the static initialization of a standard CEL compiler and runtime. The compiler is configured with a variable 'x' of type INT and a 'request' variable of type AttributeContext.Request. The runtime is also configured with the same message types.

```java
import com.google.api.expr.cel.common.types.SimpleType;
import com.google.api.expr.cel.common.types.StructTypeReference;
import com.google.api.expr.cel.compiler.CelCompiler;
import com.google.api.expr.cel.compiler.CelCompilerFactory;
import com.google.api.expr.cel.runtime.CelRuntime;
import com.google.api.expr.cel.runtime.CelRuntimeFactory;
import com.google.rpc.context.AttributeContext;

// ... inside a class, e.g., Exercise8

private static final CelCompiler CEL_COMPILER = 
    CelCompilerFactory.standardCelCompilerBuilder()
        .addVar("x", SimpleType.INT)
        .addVar(
            "request", StructTypeReference.create("google.rpc.context.AttributeContext.Request"))
        .addMessageTypes(AttributeContext.Request.getDescriptor())
        .build();
private static final CelRuntime CEL_RUNTIME = 
    CelRuntimeFactory.standardCelRuntimeBuilder()
        .addMessageTypes(AttributeContext.Request.getDescriptor())
        .build();
```

--------------------------------

### String Index Finding

Source: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md

Finds the first occurrence of a substring within a string, returning its zero-based index or -1 if not found. An optional offset can specify the starting position for the search. An empty search string returns the starting index.

```cel
<string>.indexOf(<string>) -> <int>
<string>.indexOf(<string>, <int>) -> <int>
// Examples:
// 'hello mellow'.indexOf('')         // returns 0
// 'hello mellow'.indexOf('ello')     // returns 1
// 'hello mellow'.indexOf('jello')    // returns -1
// 'hello mellow'.indexOf('', 2)      // returns 2
// 'hello mellow'.indexOf('ello', 2)  // returns 7
// 'hello mellow'.indexOf('ello', 20) // error
```

--------------------------------

### Java - Basic CEL Compilation and Evaluation

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Demonstrates the fundamental steps of compiling a CEL expression into an Abstract Syntax Tree (AST) and then evaluating that AST. This is the starting point for using CEL in Java applications.

```java
final class Exercise1 {
  /**
   * Compile the input {@code expression} and produce an AST. This method parses and type-checks the
   * given expression to validate the syntax and type-agreement of the expression.
   *
   * @throws IllegalArgumentException If the expression is malformed due to syntactic or semantic
   *     errors.
   */
  @SuppressWarnings("DoNotCallSuggester")
  CelAbstractSyntaxTree compile(String expression) {
    throw new UnsupportedOperationException("To be implemented");
  }

  /**
   * Evaluates the compiled AST.
   *
   * @throws IllegalArgumentException If the compiled expression in AST fails to evaluate.
   */
  @SuppressWarnings("DoNotCallSuggester")
  Object eval(CelAbstractSyntaxTree ast) {
    throw new UnsupportedOperationException("To be implemented");
  }
}
```

--------------------------------

### Get First List Element

Source: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md

Returns an optional containing the first value from the list, or optional.None if the list is empty.

```CEL
<list(T)>.first() -> <Optional(T)>

// Examples:
[1, 2, 3].first().value() == 1
[].first().orValue('test') == 'test'
```

--------------------------------

### Slice List

Source: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md

Returns a new sub-list using the provided start (inclusive) and end (exclusive) indexes.

```CEL
<list>.slice(<int>, <int>) -> <list>

// Examples:
[1,2,3,4].slice(1, 3) // return [2, 3]
[1,2,3,4].slice(2, 4) // return [3, 4]
```

--------------------------------

### Mixed Literals Validation Test Setup

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Sets up a test case to validate a CEL expression containing a list with mixed literal types (integer and string). It compiles the expression and prepares to validate the resulting AST.

```java
import com.google.api.expr.cel.compiler.CelAbstractSyntaxTree;
import com.google.api.expr.cel.validator.CelValidationResult;

// Assuming exercise8 is an instance of a class that provides compile and validate methods
// and has access to CelCompiler and CelRuntime.

public class Exercise8Test {

  // Assume exercise8 is initialized elsewhere in the test class
  private Exercise8 exercise8;

  @Test
  public void validate_listHasMixedLiterals_throws() throws Exception {
    CelAbstractSyntaxTree ast = exercise8.compile("3 in [1, 2, '3']");

    // Note that `CelValidationResult` is the same result class used for the compilation path.
    // This means you could alternatively invoke `.getAst()` and handle `CelValidationException` as
    // usual.
    CelValidationResult validationResult = exercise8.validate(ast);

    // Further assertions would follow here to check validationResult.
  }
}
```

--------------------------------

### CEL Logical OR Short-Circuiting (Success Cases)

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Illustrates CEL's commutative logical operators, specifically the OR operator, and how it short-circuits evaluation to return a logical result even when a branch encounters an error. This example shows successful evaluations.

```java
/**
 * Demonstrates CEL's unique feature of commutative logical operators.
 *
 * <p>If a logical operation can short-circuit a branch that results in an error, CEL evaluation
 * will return the logical result instead of propagating the error.
 */
@Test
@TestParameters("{expression: 'true || true', expectedResult: true}")
@TestParameters("{expression: 'true || false', expectedResult: true}")
@TestParameters("{expression: 'false || true', expectedResult: true}")
@TestParameters("{expression: 'false || false', expectedResult: false}")
@TestParameters("{expression: 'true || (1 / 0 > 2)', expectedResult: true}")
@TestParameters({"expression: '(1 / 0 > 2) || true', expectedResult: true}")
public void evaluate_logicalOrShortCircuits_success(String expression, boolean expectedResult) {
  Object evaluatedResult = exercise3.compileAndEvaluate(expression);

  assertThat(evaluatedResult).isEqualTo(expectedResult);
}
```

--------------------------------

### CEL Error for Unknown Overload

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

This is an example of an error message encountered in CEL when a function overload is not found in the runtime environment. It indicates that the 'contains' function with the signature 'map_contains_key_value' is missing.

```cel
> evaluation error at <input>:28: [internal] Unknown overload id 'map_contains_key_value' for function 'contains'
```

--------------------------------

### Creating MessageLiteDescriptor Instances

Source: https://github.com/google/cel-java/blob/main/protobuf/src/main/java/dev/cel/protobuf/templates/cel_lite_descriptor_template.txt

This snippet illustrates the creation of `MessageLiteDescriptor` objects. Each message descriptor is initialized with its proto type name and a list of its field descriptors. It also includes a supplier for the message's builder, if available.

```java
descriptors.add(
  new MessageLiteDescriptor(
    "${descriptor_metadata.protoTypeName}",
    fieldDescriptors,
    <#if descriptor_metadata.javaClassName??>
    ${descriptor_metadata.javaClassName}::newBuilder
    <#else>
    () -> null
    </#if>
    )
);

```

--------------------------------

### Get Last List Element

Source: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md

Returns an optional containing the last value from the list, or optional.None if the list is empty. This is syntactic sugar for accessing the element at index list.size()-1.

```CEL
<list(T)>.last() -> <Optional(T)>

// Examples:
[1, 2, 3].last().value() == 3
[].last().orValue('test') == 'test'
```

--------------------------------

### Initializing the CEL Validator

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Shows how to statically initialize a CEL validator by providing the previously configured CEL compiler and runtime instances to the validator builder.

```java
import com.google.api.expr.cel.validator.CelValidator;
import com.google.api.expr.cel.validator.CelValidatorFactory;

// ... assuming CEL_COMPILER and CEL_RUNTIME are defined as above

// Just like the compiler and runtime, the validator and optimizer can be statically
// initialized as their instances are immutable.
private static final CelValidator CEL_VALIDATOR = 
    CelValidatorFactory.standardCelValidatorBuilder(CEL_COMPILER, CEL_RUNTIME)
        .build();
```

--------------------------------

### Enabling Standard Macros in CEL Java

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

Demonstrates the best practice for enabling macros in CEL Java. It highlights the use of `CelStandardMacro.STANDARD_MACROS` and advises explicitly enabling only necessary macros for specific use cases to ensure safety and clarity.

```java
import com.google.api.expr.v1alpha1.CelStandardMacro;

// Best practice: Enable only required macros for your use case.
// CelStandardMacro.STANDARD_MACROS enables all listed macros, but explicit enabling is safer.
// Example of explicit enabling (replace with actual macro enabling logic):
// CelConfiguration.Builder celConfigBuilder = CelConfiguration.newBuilder();
// celConfigBuilder.addMacroExtensions(CelStandardMacro.LIST_CONTAINS);
// celConfigBuilder.addMacroExtensions(CelStandardMacro.OPTIONAL_GET);
// CelEnvironment cel = celConfigBuilder.build().getEnvironment();
```

--------------------------------

### CEL Standard Macros Reference

Source: https://github.com/google/cel-java/blob/main/codelab/README.md

A reference table detailing the available standard macros in CEL, their signatures, and a brief description of their functionality. This includes macros for iteration, filtering, and presence testing.

```APIDOC
Macro        | Signature                 | Description                       
------------|---------------------------|---------------------------------- 
`all`        | `r.all(var, cond)`        | Test if `cond` evaluates `true` for *all* `var` in range `r`. 
`exists`     | `r.exists(var, cond)`     | Test if `cond` evaluates `true` for *any* `var` in range `r`. 
`exists_one` | `r.exists_one(var, cond)` | Test if `cond` evaluates `true` for *only one* `var` in range `r`. 
`filter`     | `r.filter(var, cond)`     | For lists, create a new list where each element `var` in range `r` satisfies the condition `cond`. For maps, create a new list where each key `var` in range `r` satisfies the condition `cond`. 
`map`        | `r.map(var, expr)`        | Create a new list where each each `var` in range `r` is transformed by `expr`. 
             | `r.map(var, cond, expr)`  | Same as two-arg `map` but with a conditional `cond` filter before the value is transformed. 
`has`        | `has(a.b)`                | Presence test for `b` on value `a` \: For maps, json tests definition. For protos, tests non-default primitive value or a or a set message field.
```

--------------------------------

### Using CEL Extensions in Java

Source: https://github.com/google/cel-java/blob/main/extensions/src/main/java/dev/cel/extensions/README.md

Demonstrates how to incorporate CEL extensions into the CelCompiler and CelRuntime builders in Java. This involves using the addLibraries method with predefined extension sets.

```java
CelCompilerFactory.standardCelCompilerBuilder().addLibraries(CelExtensions.strings())
CelRuntimeFactory.standardCelRuntimeBuilder().addLibraries(CelExtensions.strings())
```