7 Reasons to use Spring Arjen Poutsma SpringSource About Me - - PowerPoint PPT Presentation

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7 Reasons to use Spring Arjen Poutsma SpringSource About Me - - PowerPoint PPT Presentation

Jan 28, 2024 413 likes •1.55k views

7 Reasons to use Spring Arjen Poutsma SpringSource About Me Fifteen years of experience in Enterprise Software Development Development lead of Spring Web Services Developer on Spring 3 Contributor to various Open Source

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7 Reasons to use Spring

Arjen Poutsma SpringSource

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About Me

  • Fifteen years of experience in Enterprise

Software Development

  • Development lead of Spring Web Services
  • Developer on Spring 3
  • Contributor to various Open Source

frameworks: (XFire, Axis2, NEO, ...)

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About Spring

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Aims of Spring

  • Reduce the complexity
  • f Java J2EE development
  • Simplify without

sacrificing power

  • Facilitate best

practices

  • Grew from practical

experience

Simple things should be simple. Complex things should be possible. Alan Kay

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Technical Aims of Spring

  • Write POJOs
  • Apply Java EE services to POJOs
  • Make it transactional
  • Expose via JMX
  • ...
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POJO development

  • Plain Old Java Object
  • Not bound to any environment
  • No environment-specific imports
  • Not dependent on lookup mechanism
  • Dependencies are injected
  • Prolongs life
  • Test out of the container
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Modular

  • Spring is not a “package deal”
  • All features can be used independently
  • Though they strengthen each other
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Reason #1 Dependency Injection

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The Case for Dependency Injection

  • Applications consist of multiple

components

  • How obtain these dependencies?
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Pull Configuration

  • JNDI lookup
  • Properties file
  • Service Locator anti-pattern
  • Many issues
  • Most importantly: hard to test
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Solution: Dependency Injection

  • Rather than lookup dependencies
  • Let something give them to me
  • Spring
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How Spring Works

Spring Application Context

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How Spring Works

Spring Application Context Your Application Classes (POJOs)

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How Spring Works

Spring Application Context Configuration Instructions Your Application Classes (POJOs)

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How Spring Works

Spring Application Context Configuration Instructions Your Application Classes (POJOs) Fully configured application system Ready for use Creates

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Example

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Example

public class TransferServiceImpl implements TransferService { public TransferServiceImpl(AccountRepository ar) { this.accountRepository = ar; } … }

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Example

public class TransferServiceImpl implements TransferService { public TransferServiceImpl(AccountRepository ar) { this.accountRepository = ar; } … }

Needed to perform money transfers between accounts

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Example

public class TransferServiceImpl implements TransferService { public TransferServiceImpl(AccountRepository ar) { this.accountRepository = ar; } … } public class JdbcAccountRepository implements AccountRepository { public JdbcAccountRepository(DataSource ds) { this.dataSource = ds; } … }

Needed to perform money transfers between accounts

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Example

public class TransferServiceImpl implements TransferService { public TransferServiceImpl(AccountRepository ar) { this.accountRepository = ar; } … } public class JdbcAccountRepository implements AccountRepository { public JdbcAccountRepository(DataSource ds) { this.dataSource = ds; } … }

Needed to load accounts from the database Needed to perform money transfers between accounts

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Example

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Example

<beans> <bean id=“transferService” class=“app.impl.TransferServiceImpl”> <constructor-arg ref=“accountRepository” /> </bean> <bean id=“accountRepository” class=“app.impl.JdbcAccountRepository”> <constructor-arg ref=“dataSource” /> </bean> <bean id=“dataSource” class=“com.oracle.jdbc.pool.OracleDataSource”> <property name=“URL” value=“jdbc:oracle:thin:@localhost:1521:BANK” /> <property name=“user” value=“moneytransfer-app” /> </bean> </beans>

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“Spring Sucks!”

  • Spring is XML
  • XML is Evil
  • Being Evil sucks
  • Therefore, Spring sucks
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Spring != XML

  • @Component
  • @Autowired
  • JSR-250
  • @Resource
  • @PostContruct/@PreDestroy
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@Component @Autowired

@Component public class TransferServiceImpl implements TransferService @Autowired public TransferServiceImpl(AccountRepository ar) { this.accountRepository = ar; } … }

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Why not use Java EE Dependency Injection?

  • Testing, inside IDE
  • Java EE only allows injection of JNDI-

managed objects

  • Spring injects everything
  • Primitives (configuration)
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Reason #2 JdbcTemplate

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JDBC

  • Object/Relational Mapping is popular
  • But JDBC continues to be important
  • Batch Operations
  • Set-based operations
  • Stored procedures
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21

Redundant, Error Prone Code

public List findByLastName(String lastName) { List personList = new ArrayList(); Connection conn = null; String sql = “select first_name, age from PERSON where last_name=?“; try { DataSource dataSource = DataSourceUtils.getDataSource(); conn = dataSource.getConnection(); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, lastName); ResultSet rs = ps.executeQuery(); while (rs.next()) { String firstName = rs.getString(”first_name“); int age = rs.getInt(“age”); personList.add(new Person(firstName, lastName, age)); } } catch (Exception e) { /* ??? */ } finally { try { conn.close(); } catch (SQLException e) { /* ??? */ } } return personList; }

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Redundant, Error Prone Code

public List findByLastName(String lastName) { List personList = new ArrayList(); Connection conn = null; String sql = "select first_name, age from PERSON where last_name=?"; try { DataSource dataSource = DataSourceUtils.getDataSource(); conn = dataSource.getConnection(); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, lastName); ResultSet rs = ps.executeQuery(); while (rs.next()) { String firstName = rs.getString(“first_name”); int age = rs.getInt(“age”); personList.add(new Person(firstName, lastName, age)); } } catch (Exception e) { /* ??? */ } finally { try { conn.close(); } catch (SQLException e) { /* ??? */ } } return personList; }

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22

Redundant, Error Prone Code

public List findByLastName(String lastName) { List personList = new ArrayList(); Connection conn = null; String sql = "select first_name, age from PERSON where last_name=?"; try { DataSource dataSource = DataSourceUtils.getDataSource(); conn = dataSource.getConnection(); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, lastName); ResultSet rs = ps.executeQuery(); while (rs.next()) { String firstName = rs.getString(“first_name”); int age = rs.getInt(“age”); personList.add(new Person(firstName, lastName, age)); } } catch (Exception e) { /* ??? */ } finally { try { conn.close(); } catch (SQLException e) { /* ??? */ } } return personList; }

The bold matters - the rest is boilerplate

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23

JdbcTemplate

int count = jdbcTemplate.queryForInt( “SELECT COUNT(*) FROM CUSTOMER”);

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JdbcTemplate

  • Acquisition of the connection
  • Participation in the transaction
  • Execution of the statement
  • Processing of the result set
  • Handling any exceptions
  • Release of the connection

int count = jdbcTemplate.queryForInt( “SELECT COUNT(*) FROM CUSTOMER”); All handled by Spring

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Querying With SimpleJdbcTemplate

public int getCountOfPersonsOlderThan(int age) { return jdbcTemplate().queryForInt( “select count(*) from PERSON where age > ?”, age); }

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Domain Objects

public Person getPerson(int id) { return getSimpleJdbcTemplate().queryForObject( “select first_name, last_name from PERSON where id=?”, new PersonMapper(), id); }

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Domain Objects

public Person getPerson(int id) { return getSimpleJdbcTemplate().queryForObject( “select first_name, last_name from PERSON where id=?”, new PersonMapper(), id); } class PersonMapper implements ParameterizedRowMapper<Person> { public Person mapRow(ResultSet rs, int i) { return new Person(rs.getString(1), rs.getString(2)); } }

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Reason #3 Exception Hierarchy

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27

public List findByLastName(String lastName) { List personList = new ArrayList(); Connection conn = null; String sql = "select first_name, age from PERSON where last_name=?“; try { DataSource dataSource = DataSourceUtils.getDataSource(); conn = dataSource.getConnection(); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, lastName); ResultSet rs = ps.executeQuery(); while (rs.next()) { String firstName = rs.getString(”first_name“); int age = rs.getInt(“age”); personList.add(new Person(firstName, lastName, age)); } } catch (Exception e) { /* ??? */ } finally { try { conn.close(); } catch (SQLException e) { /* ??? */ } } return personList; }

Poor Exception Handling

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27

public List findByLastName(String lastName) { List personList = new ArrayList(); Connection conn = null; String sql = "select first_name, age from PERSON where last_name=?“; try { DataSource dataSource = DataSourceUtils.getDataSource(); conn = dataSource.getConnection(); PreparedStatement ps = conn.prepareStatement(sql); ps.setString(1, lastName); ResultSet rs = ps.executeQuery(); while (rs.next()) { String firstName = rs.getString(”first_name“); int age = rs.getInt(“age”); personList.add(new Person(firstName, lastName, age)); } } catch (Exception e) { /* ??? */ } finally { try { conn.close(); } catch (SQLException e) { /* ??? */ } } return personList; }

Poor Exception Handling

What can you do?

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What can you do?

  • Nothing
  • Logging
  • Wrapping
  • Retry
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  • } catch (SQLException ex) {
  • if (ex.getErrorCode() == 60) {// check for ORA-00060
  • return findByLastName(lastName);
  • } else {
  • throw ex;
  • }
  • }

Dead Lock Loser

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Retry

  • Ugly code
  • Not portable
  • JDBC vs JPA
  • Oracle vs SQL Server
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In Spring

  • Spring does exception translation
  • Into a rich Exception Hierarchy
  • Catch DeadLockLoserException
  • Use AOP!
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DataAccessException Hierarchy (subset)

DataRetrievalFailureException DataAccessResourceFailureException CleanupFailureDataAccessException InvalidDataAccessApiUsageException InvalidDataAccessResourceUsageException IncorrectUpdateSemanticsDataAccessException TypeMismatchDataAccessException OptimisticLockingFailureException ObjectRetrievalFailureException DataAccessException UncategorizedDataAccessException DataIntegrityViolationException DeadlockLoserDataAccessException ObjectOptimisticLockingFailureException

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Reason #4 Aspect-Oriented Programming

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What Problem Does AOP Solve?

Aspect-Oriented Programming (AOP) enables modularization of cross-cutting concerns

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What are Cross- Cutting Concerns?

Generic functionality that is needed in many places in your application

  • Logging and Tracing
  • Transaction Management

Security

  • Caching
  • Error Handling
  • Performance Monitoring
  • Custom Business Rules
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An Example Requirement

  • Perform a role-based security check before

every application method

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An Example Requirement

  • Perform a role-based security check before

every application method

A sign this requirement is a cross-cutting concern

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Without AOP

  • Failing to modularize cross-cutting

concerns leads to two things

  • Code tangling
  • A coupling of concerns
  • Code scattering
  • The same concern spread across

modules

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Tangling

public class RewardNetworkImpl implements RewardNetwork { public RewardConfirmation rewardAccountFor(Dining dining) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } Account a = accountRepository.findByCreditCard(… Restaurant r = restaurantRepository.findByMerchantNumber(… MonetaryAmount amt = r.calculateBenefitFor(account, dining); … } }

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Tangling

public class RewardNetworkImpl implements RewardNetwork { public RewardConfirmation rewardAccountFor(Dining dining) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } Account a = accountRepository.findByCreditCard(… Restaurant r = restaurantRepository.findByMerchantNumber(… MonetaryAmount amt = r.calculateBenefitFor(account, dining); … } }

Mixing of concerns

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Scattering

public class HibernateAccountManager implements AccountManager { public Account getAccountForEditing(Long id) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } … public class HibernateMerchantReportingService implements MerchantReportingService { public List<DiningSummary> findDinings(String merchantNumber, DateInterval interval) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } …

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Scattering

public class HibernateAccountManager implements AccountManager { public Account getAccountForEditing(Long id) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } … public class HibernateMerchantReportingService implements MerchantReportingService { public List<DiningSummary> findDinings(String merchantNumber, DateInterval interval) { if (!hasPermission(SecurityContext.getPrincipal()) { throw new AccessDeniedException(); } …

Duplication

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40 BankService

Without AOP

CustomerService ReportingService

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40 BankService

Without AOP

Security

CustomerService ReportingService

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40 BankService

Without AOP

Transactions Security

CustomerService ReportingService

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40 BankService

Without AOP

Transactions Security Logging

CustomerService ReportingService

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40 BankService

Without AOP

Code scattering Transactions Security Logging

CustomerService ReportingService

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40 BankService

Without AOP

Code scattering Code tangling Transactions Security Logging

CustomerService ReportingService

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How AOP Works

1.Implement your mainline application logic 2.Write aspects to implement your cross-

cutting concerns

3.Weave the aspects into your application

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AOP based

BankService CustomerService ReportingService

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42

AOP based

Security Aspect BankService CustomerService ReportingService

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42

AOP based

Transaction Aspect Security Aspect BankService CustomerService ReportingService

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42

AOP based

Transaction Aspect Security Aspect Logging Aspect BankService CustomerService ReportingService

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42

AOP based

Transaction Aspect Security Aspect Logging Aspect BankService CustomerService ReportingService

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AOP Quick Start

  • Consider this basic requirement
  • How can you use AOP to meet it?

Log a message every time a property is about to change

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Target Object

public class SimpleCache implements Cache { private int cacheSize; private DataSource dataSource; public void setCacheSize(int size) { cacheSize = size; } public void setDataSource(DataSource ds) { dataSource = ds; } … }

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The Aspect

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The Aspect

@Aspect

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The Aspect

@Aspect public class PropertyChangeTracker {

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass());

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass());

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass()); @Before(“execution(void set*(*))”)

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass()); @Before(“execution(void set*(*))”) public void trackChange() {

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass()); @Before(“execution(void set*(*))”) public void trackChange() { logger.info(“Property about to change…”);

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass()); @Before(“execution(void set*(*))”) public void trackChange() { logger.info(“Property about to change…”); }

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The Aspect

@Aspect public class PropertyChangeTracker { private Logger logger = Logger.getLogger(getClass()); @Before(“execution(void set*(*))”) public void trackChange() { logger.info(“Property about to change…”); } }

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<beans> <aop:aspectj-autoproxy/> <bean id=“propertyChangeTracker” class=“example.PropertyChangeTracker” /> <bean name=“cache-A” class=“example.SimpleCache” ../> <bean name=“cache-B” class=“example.SimpleCache” ../> <bean name=“cache-C” class=“example.SimpleCache” ../> </beans>

Tell Spring about the Aspect

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Run...

ApplicationContext context = new ClassPathXmlApplicationContext(“application-config.xml”); Cache cache = (Cache) context.getBean(“cache-A”); cache.setCacheSize(2500);

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Run...

ApplicationContext context = new ClassPathXmlApplicationContext(“application-config.xml”); Cache cache = (Cache) context.getBean(“cache-A”); cache.setCacheSize(2500); INFO: Property about to change…

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Reason #5 @Transactional

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Why use Transactions?

  • Atomic

–Each unit of work is an all-or-nothing operation

  • Consistent

–Database integrity constraints are never violated

  • Isolated

–Uncommitted changes are not visible to other transactions

  • Durable

–Committed changes are permanent

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Local Transaction Management

  • Transactions can be managed at the level of a

local resource –Such as the database

  • Requires programmatic management of

transactional behavior on the Connection

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Example

public void updateBeneficiaries(Account account) { ... try { conn = dataSource.getConnection(); conn.setAutoCommit(false); ps = conn.prepareStatement(sql); for (Beneficiary b : account.getBeneficiaries()) { ps.setBigDecimal(1, b.getSavings().asBigDecimal()); ps.setLong(2, account.getEntityId()); ps.setString(3, b.getName()); ps.executeUpdate(); } conn.commit(); } catch (Exception e) { conn.rollback(); throw new RuntimeException(“Error updating!”, e); }

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Problems with Local Transactions

  • Connection management code is error-prone
  • Transaction demarcation belongs at the

service layer –Multiple data access methods may be called within a transaction –Connection must be managed at a higher level

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Passing Connections

public RewardConfirmation rewardAccountFor(Dining dining) { Connection conn = DataSourceUtils.getConnection(); conn.setAutoCommit(false); try { ... accountRepository.updateBeneficiaries(account, conn); rc = rewardRepository.confirmReward(contrib, dining, conn); conn.commit(); } catch (Exception e) { conn.rollback(); throw new RuntimeException(“reward failed”, e); } }

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Programmatic JTA

  • Application Servers enable use of the Java

Transaction API (JTA)

  • The UserTransaction object is bound to

JNDI

  • Transactions can be managed from the

service layer

  • May call multiple data access methods
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JTA

public RewardConfirmation rewardAccountFor(Dining dining) { Context ctx = new InitialContext(); UserTransaction transaction = (UserTransaction) ctx.lookup(“java:comp/UserTransaction”); transaction.begin(); try { ... accountRepository.updateBeneficiaries(account); confirmation = rewardRepository.confirmReward(contribution, dining); transaction.commit(); } catch (Exception e) { transaction.rollback(); throw new RuntimeException(“failed to reward”, e); } }

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Programmatic JTA Problems

  • Depends on an Application Server

environment

  • Still requires code to manage transactions
  • The code is error-prone
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@Transactional

public class RewardNetworkImpl implements RewardNetwork { @Transactional public RewardConfirmation rewardAccountFor(Dining d) { // atomic unit-of-work } }

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@Transactional

  • Works though AOP
  • Consistent approach
  • JDBC
  • JPA
  • Hibernate
  • JMS
  • JTA
  • ...
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Reason #6 Scripting Languages

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Scripting Languages

  • More and more popular
  • Especially when running on the JVM
  • Mix-and-match approach
  • Front-end in JRuby
  • Back-end in Java
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Dynamic Language Support in Spring

  • Spring container supports
  • Groovy
  • JRuby
  • BeanShell
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JRuby

package org.springframework.scripting; public interface Messenger { String getMessage(); } require 'java' class RubyMessenger include org.springframework.scripting.Messenger def setMessage(message) @@message = message end def getMessage @@message end end <lang:jruby id="messageService" script-interfaces="org.springframework.scripting.Messenger" script-source="classpath:RubyMessenger.rb"> <lang:property name="message" value="Hello World!" /> </lang:jruby>

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Reason #7 OSGi

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JAR Hell

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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JAR Hell

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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JAR Hell

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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OSGi

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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OSGi

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

MANIFEST.MF Import-package:

  • rg.apache.log4j;

version=1.2.13

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OSGi

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

MANIFEST.MF Import-package:

  • rg.apache.log4j;

version=1.2.13 MANIFEST.MF Import-package:

  • rg.apache.log4j;

version=1.2.15

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OSGi

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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OSGi

Your Application Spring 2.5.4 Hibernate 3.3.0 log4j 1.2.13 log4j 1.2.15

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66

OSGi Service contribution

Published services Private implementation

  • bjects
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OSGitm – Dynamic System for Java

  • Partition an app into modules
  • Module = Bundle = Jar = a set of classes
  • Each module has its own:
  • class space
  • lifecycle
  • Strict visibility rules
  • Understands versioning
  • Everything is Dynamic!
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OSGi

  • Import specific versions of dependencies
  • Export as services
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Spring Dynamic Modules

  • Decorate objects as OSGi services
  • Dependency injection for OSGi services
  • Remove OSGi dependencies
  • Easier to test
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Exporting OSGi Service

<bean id=“myPojo” class=“someObject”/> <osgi:service ref=“myPojo” interface= “com.springsource.MyService"/>

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Importing OSGi service

<osgi:reference id=“osgiService" interface=“com.springsource.DynamicService"/> <bean id=“consumer” class..> <property name=“service” ref=“osgiService”> </bean>

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But wait, there is more!

  • There is more!
  • JMS, Web, Security, Web Services, Batch,

Integration, ...

  • Check out www.springframework.org
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Q & A