fix: make compiled statements immutable (#843)

Author: olavloite

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ClientSideStatementExecutor.java

@@ -16,26 +16,13 @@
 
 package com.google.cloud.spanner.connection;
 
-import com.google.cloud.spanner.connection.ClientSideStatementImpl.CompileException;
-
 /**
  * A {@link ClientSideStatementExecutor} is used to compile {@link ClientSideStatement}s from the
  * json source file, and to execute these against a {@link Connection} (through a {@link
  * ConnectionStatementExecutor}).
  */
 interface ClientSideStatementExecutor {
 
-  /**
-   * Compiles the given {@link ClientSideStatementImpl} and registers this statement with this
-   * executor. A statement must be compiled before it can be executed. The parser automatically
-   * compiles all available statements during initialization.
-   *
-   * @param statement The statement to compile.
-   * @throws CompileException If the statement could not be compiled. This should never happen, as
-   *     it would indicate that an invalid statement has been defined in the source file.
-   */
-  void compile(ClientSideStatementImpl statement) throws CompileException;
-
   /**
    * Executes the {@link ClientSideStatementImpl} that has been compiled and registered with this
    * executor on the specified connection.

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ClientSideStatementImpl.java

@@ -19,6 +19,7 @@
 import com.google.cloud.spanner.SpannerException;
 import com.google.cloud.spanner.connection.StatementResult.ResultType;
 import com.google.common.base.Preconditions;
+import java.lang.reflect.Constructor;
 import java.lang.reflect.InvocationTargetException;
 import java.util.Collections;
 import java.util.List;
@@ -143,10 +144,12 @@ public String getMessage() {
   ClientSideStatementImpl compile() throws CompileException {
     try {
       this.pattern = Pattern.compile(regex);
-      this.executor =
-          (ClientSideStatementExecutor)
-              Class.forName(getClass().getPackage().getName() + "." + executorName).newInstance();
-      this.executor.compile(this);
+      @SuppressWarnings("unchecked")
+      Constructor<ClientSideStatementExecutor> constructor =
+          (Constructor<ClientSideStatementExecutor>)
+              Class.forName(getClass().getPackage().getName() + "." + executorName)
+                  .getDeclaredConstructor(ClientSideStatementImpl.class);
+      this.executor = constructor.newInstance(this);
       return this;
     } catch (Exception e) {
       throw new CompileException(e, this);

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ClientSideStatementNoParamExecutor.java

@@ -24,12 +24,16 @@
  * SHOW AUTOCOMMIT. The executor just calls a method with no parameters.
  */
 class ClientSideStatementNoParamExecutor implements ClientSideStatementExecutor {
-  private Method method;
+  private final Method method;
 
-  ClientSideStatementNoParamExecutor() {}
-
-  @Override
-  public void compile(ClientSideStatementImpl statement) throws CompileException {
+  /**
+   * Creates and compiles the given {@link ClientSideStatementImpl}.
+   *
+   * @param statement The statement to compile.
+   * @throws CompileException If the statement could not be compiled. This should never happen, as
+   *     it would indicate that an invalid statement has been defined in the source file.
+   */
+  ClientSideStatementNoParamExecutor(ClientSideStatementImpl statement) throws CompileException {
     try {
       this.method = ConnectionStatementExecutor.class.getDeclaredMethod(statement.getMethodName());
     } catch (NoSuchMethodException | SecurityException e) {

google-cloud-spanner/src/main/java/com/google/cloud/spanner/connection/ClientSideStatementSetExecutor.java

@@ -30,14 +30,20 @@
  * AUTOCOMMIT=TRUE.
  */
 class ClientSideStatementSetExecutor<T> implements ClientSideStatementExecutor {
-  private ClientSideStatementImpl statement;
-  private Method method;
-  private ClientSideStatementValueConverter<T> converter;
-  private Pattern allowedValuesPattern;
+  private final ClientSideStatementImpl statement;
+  private final Method method;
+  private final ClientSideStatementValueConverter<T> converter;
+  private final Pattern allowedValuesPattern;
 
+  /**
+   * Creates and compiles the given {@link ClientSideStatementImpl}.
+   *
+   * @param statement The statement to compile.
+   * @throws CompileException If the statement could not be compiled. This should never happen, as
+   *     it would indicate that an invalid statement has been defined in the source file.
+   */
   @SuppressWarnings("unchecked")
-  @Override
-  public void compile(ClientSideStatementImpl statement) throws CompileException {
+  ClientSideStatementSetExecutor(ClientSideStatementImpl statement) throws CompileException {
     Preconditions.checkNotNull(statement.getSetStatement());
     try {
       this.statement = statement;