Create IAM policies with the Amazon SDK for Java 2.x
The IAM Policy Builder API
Instead of building an IAM policy by manually assembling a JSON string or by reading a file,
the API provides a client-side, object-oriented approach to generate the JSON string. When you
read an existing IAM policy in JSON format, the API converts it to an IamPolicy
The IAM Policy Builder API became available with version 2.20.105 of the SDK, so use that
version or a later one in your Maven build file. The latest version number of the SDK is listed
on Maven central
The following snippet shows an example dependency block for a Maven pom.xml
file. This allows you to use the IAM Policy Builder API in your project.
<dependency> <groupId>software.amazon.awssdk</groupId> <artifactId>iam-policy-builder</artifactId> <version>2.27.21</version> </dependency>
Create an IamPolicy
This section shows several examples of how to build policies by using the IAM Policy Builder API.
In each of the following examples, start with the IamPolicy.Builder and add one or more statements by using the
addStatement method. Following this pattern, the IamStatement.Builder
Example: Create a time-based policy
The following example creates an identity-based policy that permits the Amazon DynamoDB
GetItem action between two points in time.
public String timeBasedPolicyExample() { IamPolicy policy = IamPolicy.builder() .addStatement(b -> b .effect(IamEffect.ALLOW) .addAction("dynamodb:GetItem") .addResource(IamResource.ALL) .addCondition(b1 -> b1 .operator(IamConditionOperator.DATE_GREATER_THAN) .key("aws:CurrentTime") .value("2020-04-01T00:00:00Z")) .addCondition(b1 -> b1 .operator(IamConditionOperator.DATE_LESS_THAN) .key("aws:CurrentTime") .value("2020-06-30T23:59:59Z"))) .build(); // Use an IamPolicyWriter to write out the JSON string to a more readable format. return policy.toJson(IamPolicyWriter.builder() .prettyPrint(true) .build()); }
The last statement in the previous example returns the following JSON string.
Read more about this example in the Amazon Identity and Access Management User Guide.
{ "Version" : "2012-10-17", "Statement" : { "Effect" : "Allow", "Action" : "dynamodb:GetItem", "Resource" : "*", "Condition" : { "DateGreaterThan" : { "aws:CurrentTime" : "2020-04-01T00:00:00Z" }, "DateLessThan" : { "aws:CurrentTime" : "2020-06-30T23:59:59Z" } } }
Example: Specify multiple conditions
The following example shows how you can create an identity-based policy that allows access to specific DynamoDB attributes. The policy contains two conditions.
public String multipleConditionsExample() { IamPolicy policy = IamPolicy.builder() .addStatement(b -> b .effect(IamEffect.ALLOW) .addAction("dynamodb:GetItem") .addAction("dynamodb:BatchGetItem") .addAction("dynamodb:Query") .addAction("dynamodb:PutItem") .addAction("dynamodb:UpdateItem") .addAction("dynamodb:DeleteItem") .addAction("dynamodb:BatchWriteItem") .addResource("arn:aws:dynamodb:*:*:table/table-name") .addConditions(IamConditionOperator.STRING_EQUALS.addPrefix("ForAllValues:"), "dynamodb:Attributes", List.of("column-name1", "column-name2", "column-name3")) .addCondition(b1 -> b1.operator(IamConditionOperator.STRING_EQUALS.addSuffix("IfExists")) .key("dynamodb:Select") .value("SPECIFIC_ATTRIBUTES"))) .build(); return policy.toJson(IamPolicyWriter.builder() .prettyPrint(true).build()); }
The last statement in the previous example returns the following JSON string.
Read more about this example in the Amazon Identity and Access Management User Guide.
{ "Version" : "2012-10-17", "Statement" : { "Effect" : "Allow", "Action" : [ "dynamodb:GetItem", "dynamodb:BatchGetItem", "dynamodb:Query", "dynamodb:PutItem", "dynamodb:UpdateItem", "dynamodb:DeleteItem", "dynamodb:BatchWriteItem" ], "Resource" : "arn:aws:dynamodb:*:*:table/table-name", "Condition" : { "ForAllValues:StringEquals" : { "dynamodb:Attributes" : [ "column-name1", "column-name2", "column-name3" ] }, "StringEqualsIfExists" : { "dynamodb:Select" : "SPECIFIC_ATTRIBUTES" } } }
Example: Specify principals
The following example shows how to create a resource-based policy that denies access to a bucket for all principals except for those specified in the condition.
public String specifyPrincipalsExample() { IamPolicy policy = IamPolicy.builder() .addStatement(b -> b .effect(IamEffect.DENY) .addAction("s3:*") .addPrincipal(IamPrincipal.ALL) .addResource("arn:aws:s3:::BUCKETNAME/*") .addResource("arn:aws:s3:::BUCKETNAME") .addCondition(b1 -> b1 .operator(IamConditionOperator.ARN_NOT_EQUALS) .key("aws:PrincipalArn") .value("arn:aws:iam::444455556666:user/user-name"))) .build(); return policy.toJson(IamPolicyWriter.builder() .prettyPrint(true).build()); }
The last statement in the previous example returns the following JSON string.
Read more about this example in the Amazon Identity and Access Management User Guide.
{ "Version" : "2012-10-17", "Statement" : { "Effect" : "Deny", "Principal" : "*", "Action" : "s3:*", "Resource" : [ "arn:aws:s3:::BUCKETNAME/*", "arn:aws:s3:::BUCKETNAME" ], "Condition" : { "ArnNotEquals" : { "aws:PrincipalArn" : "arn:aws:iam::444455556666:user/user-name" } } } }
Example: Allow cross-account access
The following example shows how to allow another Amazon Web Services account to upload objects to your bucket while retaining full owner control of the uploaded objects.
public String allowCrossAccountAccessExample() { IamPolicy policy = IamPolicy.builder() .addStatement(b -> b .effect(IamEffect.ALLOW) .addPrincipal(IamPrincipalType.AWS, "111122223333") .addAction("s3:PutObject") .addResource("arn:aws:s3:::amzn-s3-demo-bucket/*") .addCondition(b1 -> b1 .operator(IamConditionOperator.STRING_EQUALS) .key("s3:x-amz-acl") .value("bucket-owner-full-control"))) .build(); return policy.toJson(IamPolicyWriter.builder() .prettyPrint(true).build()); }
The last statement in the previous example returns the following JSON string.
Read more about this example in the Amazon Simple Storage Service User Guide.
{ "Version" : "2012-10-17", "Statement" : { "Effect" : "Allow", "Principal" : { "AWS" : "111122223333" }, "Action" : "s3:PutObject", "Resource" : "arn:aws:s3:::amzn-s3-demo-bucket/*", "Condition" : { "StringEquals" : { "s3:x-amz-acl" : "bucket-owner-full-control" } } } }
Use an IamPolicy with
IAM
After you have created a IamPolicy instance, you use an IamClient
The following example builds a policy that allows an IAM identity to write
items to a DynamoDB table in the account that is specified with the accountID
parameter. The policy is then uploaded to IAM as a JSON string.
public String createAndUploadPolicyExample(IamClient iam, String accountID, String policyName) { // Build the policy. IamPolicy policy = IamPolicy.builder() // 'version' defaults to "2012-10-17". .addStatement(IamStatement.builder() .effect(IamEffect.ALLOW) .addAction("dynamodb:PutItem") .addResource("arn:aws:dynamodb:us-east-1:" + accountID + ":table/exampleTableName") .build()) .build(); // Upload the policy. iam.createPolicy(r -> r.policyName(policyName).policyDocument(policy.toJson())); return policy.toJson(IamPolicyWriter.builder().prettyPrint(true).build()); }
The next example builds on the previous example. The code downloads the policy and uses it as the basis for a new policy by copying and altering the statement. The new policy is then uploaded.
public String createNewBasedOnExistingPolicyExample(IamClient iam, String accountID, String policyName, String newPolicyName) { String policyArn = "arn:aws:iam::" + accountID + ":policy/" + policyName; GetPolicyResponse getPolicyResponse = iam.getPolicy(r -> r.policyArn(policyArn)); String policyVersion = getPolicyResponse.policy().defaultVersionId(); GetPolicyVersionResponse getPolicyVersionResponse = iam.getPolicyVersion(r -> r.policyArn(policyArn).versionId(policyVersion)); // Create an IamPolicy instance from the JSON string returned from IAM. String decodedPolicy = URLDecoder.decode(getPolicyVersionResponse.policyVersion().document(), StandardCharsets.UTF_8); IamPolicy policy = IamPolicy.fromJson(decodedPolicy); /* All IamPolicy components are immutable, so use the copy method that creates a new instance that can be altered in the same method call. Add the ability to get an item from DynamoDB as an additional action. */ IamStatement newStatement = policy.statements().get(0).copy(s -> s.addAction("dynamodb:GetItem")); // Create a new statement that replaces the original statement. IamPolicy newPolicy = policy.copy(p -> p.statements(Arrays.asList(newStatement))); // Upload the new policy. IAM now has both policies. iam.createPolicy(r -> r.policyName(newPolicyName) .policyDocument(newPolicy.toJson())); return newPolicy.toJson(IamPolicyWriter.builder().prettyPrint(true).build()); }
The previous examples use an IamClient argument that is created as shown
in the following snippet.
IamClient iam = IamClient.builder().region(Region.AWS_GLOBAL).build();
The examples return the following JSON strings.
First example { "Version" : "2012-10-17", "Statement" : { "Effect" : "Allow", "Action" : "dynamodb:PutItem", "Resource" : "arn:aws:dynamodb:us-east-1:111122223333:table/exampleTableName" } } Second example { "Version" : "2012-10-17", "Statement" : { "Effect" : "Allow", "Action" : [ "dynamodb:PutItem", "dynamodb:GetItem" ], "Resource" : "arn:aws:dynamodb:us-east-1:111122223333:table/exampleTableName" } }