Spring Batch自定义ItemReader Spring Batch 怎样自定义ItemReader

时间:2021-09-07 梦想画家人气:0

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Spring Batch 自定义ItemReader

Spring Batch支持各种数据输入源，如文件、数据库等。然而有时也会遇到一些默认不支持的数据源，这时我们则需要实现自己的数据源————自定义ItemReader。本文通过示例说明如何自定义ItemReader。

创建自定义ItemReader

创建自定义ItemReader需要下面两个步骤：

创建一个实现ItemReader接口的类，并提供返回对象类型 T 作为类型参数。
按照下面规则实现ItemReader接口的T read()方法

read()方法如果存在下一个对象则返回，否则返回null。

下面我们自定义ItemReader，其返回在线测试课程的学生信息StuDto类型，为了减少复杂性，该数据存储在内存中。StuDto类是一个简单数据传输对象，代码如下：

@Data
public class StuDTO {
    private String emailAddress;
    private String name;
    private String purchasedPackage;
}

下面参照一下步骤创建ItemReader:

创建InMemoryStudentReader 类
实现ItemReader接口，并设置返回对象类型为StuDto
类中增加List studentData 字段，其包括参加课程的学生信息
类中增加nextStudentIndex 字段，表示下一个StuDto对象的索引
增加私有initialize()方法，初始化学生信息并设置索引值为0
创建构造函数并调用initialize方法
实现read()方法，包括下面规则：如果存在下一个学生，则返回StuDto对象并把索引加一。否则返回null。

InMemoryStudentReader 代码如下：

public class InMemoryStudentReader implements ItemReader<StuDto> { 
    private int nextStudentIndex;
    private List<StuDto> studentData; 
    InMemoryStudentReader() {
        initialize();
    }
 
    private void initialize() {
        StuDto tony = new StuDto();
        tony.setEmailAddress("tony.tester@gmail.com");
        tony.setName("Tony Tester");
        tony.setPurchasedPackage("master");
 
        StuDto nick = new StuDto();
        nick.setEmailAddress("nick.newbie@gmail.com");
        nick.setName("Nick Newbie");
        nick.setPurchasedPackage("starter");
 
        StuDto ian = new StuDto();
        ian.setEmailAddress("ian.intermediate@gmail.com");
        ian.setName("Ian Intermediate");
        ian.setPurchasedPackage("intermediate");
 
        studentData = Collections.unmodifiableList(Arrays.asList(tony, nick, ian));
        nextStudentIndex = 0;
    }
 
    @Override
    public StuDto read() throws Exception {
        StuDto nextStudent = null;
 
        if (nextStudentIndex < studentData.size()) {
            nextStudent = studentData.get(nextStudentIndex);
            nextStudentIndex++;
        } 
        return nextStudent;
    }
}

创建好自定义ItemReader后，需要配置其作为bean让Spring Batch Job使用。下面请看如何配置。

配置ItemReader Bean

配置类代码如下：

@Configuration
public class InMemoryStudentJobConfig { 
    @Bean
    ItemReader<StuDto> inMemoryStudentReader() {
        return new InMemoryStudentReader();
    }
}

需要增加@Configuration表明类为配置类，增加方法返回ItemReader类型，并增加@Bean注解，实现方法内容————返回InMemoryStudentReader对象。

小结一下

本文通过示例说明如何自定义ItemReader，主要包括三个方面：

自定义ItemReader需实现ItemReader接口
实现ItemReader接口，需要指定返回类型作为类型参数(T)
实现接口方法read，如果存在下一个对象则返回，反之返回null

Spring Batch 之 ItemReader

重点介绍 ItemReader，如何从不同数据源读取数据；以及异常处理及重启机制。

JdbcPagingItemReader

从数据库中读取数据

@Configuration
public class DBJdbcDemoJobConfiguration {
    @Autowired
    private JobBuilderFactory jobBuilderFactory;
 
    @Autowired
    private StepBuilderFactory stepBuilderFactory;
 
    @Autowired
    @Qualifier("dbJdbcDemoWriter")
    private ItemWriter<? super Customer> dbJdbcDemoWriter;
 
    @Autowired
    private DataSource dataSource;
 
    @Bean
    public Job DBJdbcDemoJob(){
        return jobBuilderFactory.get("DBJdbcDemoJob")
                .start(dbJdbcDemoStep())
                .build();
     }
 
    @Bean
    public Step dbJdbcDemoStep() {
        return stepBuilderFactory.get("dbJdbcDemoStep")
                .<Customer,Customer>chunk(100)
                .reader(dbJdbcDemoReader())
                .writer(dbJdbcDemoWriter)
                .build();
    }
 
    @Bean
    @StepScope
    public JdbcPagingItemReader<Customer> dbJdbcDemoReader() {
        JdbcPagingItemReader<Customer> reader = new JdbcPagingItemReader<>();
 
        reader.setDataSource(this.dataSource);
        reader.setFetchSize(100); //批量读取
        reader.setRowMapper((rs,rowNum)->{
            return Customer.builder().id(rs.getLong("id"))
                    .firstName(rs.getString("firstName"))
                    .lastName(rs.getString("lastName"))
                    .birthdate(rs.getString("birthdate"))
                    .build();
 
        });
 
        MySqlPagingQueryProvider queryProvider = new MySqlPagingQueryProvider();
        queryProvider.setSelectClause("id, firstName, lastName, birthdate");
        queryProvider.setFromClause("from Customer");
        Map<String, Order> sortKeys = new HashMap<>(1);
        sortKeys.put("id", Order.ASCENDING);
        queryProvider.setSortKeys(sortKeys); 
        reader.setQueryProvider(queryProvider); 
        return reader; 
    }
}

Job 和 ItermWriter不是本文介绍重点，此处举例，下面例子相同

@Component("dbJdbcDemoWriter")
public class DbJdbcDemoWriter implements ItemWriter<Customer> {
    @Override
    public void write(List<? extends Customer> items) throws Exception {
        for (Customer customer:items)
            System.out.println(customer); 
    }
}

FlatFileItemReader

从CVS文件中读取数据

 
@Configuration
public class FlatFileDemoJobConfiguration {
    @Autowired
    private JobBuilderFactory jobBuilderFactory; 
    @Autowired
    private StepBuilderFactory stepBuilderFactory; 
    @Autowired
    @Qualifier("flatFileDemoWriter")
    private ItemWriter<? super Customer> flatFileDemoWriter; 
    @Bean
    public Job flatFileDemoJob(){
        return jobBuilderFactory.get("flatFileDemoJob")
                .start(flatFileDemoStep())
                .build(); 
    }
 
    @Bean
    public Step flatFileDemoStep() {
        return stepBuilderFactory.get("flatFileDemoStep")
                .<Customer,Customer>chunk(100)
                .reader(flatFileDemoReader())
                .writer(flatFileDemoWriter)
                .build();
    }
 
    @Bean
    @StepScope
    public FlatFileItemReader<Customer> flatFileDemoReader() {
        FlatFileItemReader<Customer> reader = new FlatFileItemReader<>();
        reader.setResource(new ClassPathResource("customer.csv"));
        reader.setLinesToSkip(1);
 
        DelimitedLineTokenizer tokenizer = new DelimitedLineTokenizer();
        tokenizer.setNames(new String[]{"id","firstName","lastName","birthdate"});
 
        DefaultLineMapper<Customer> lineMapper = new DefaultLineMapper<>();
        lineMapper.setLineTokenizer(tokenizer);
        lineMapper.setFieldSetMapper((fieldSet -> {
            return Customer.builder().id(fieldSet.readLong("id"))
                    .firstName(fieldSet.readString("firstName"))
                    .lastName(fieldSet.readString("lastName"))
                    .birthdate(fieldSet.readString("birthdate"))
                    .build();
        }));
        lineMapper.afterPropertiesSet(); 
        reader.setLineMapper(lineMapper); 
        return reader; 
    }
}

StaxEventItemReader

从XML文件中读取数据

@Configuration
public class XmlFileDemoJobConfiguration {
    @Autowired
    private JobBuilderFactory jobBuilderFactory; 
    @Autowired
    private StepBuilderFactory stepBuilderFactory; 
    @Autowired
    @Qualifier("xmlFileDemoWriter")
    private ItemWriter<? super Customer> xmlFileDemoWriter; 
    @Bean
    public Job xmlFileDemoJob(){
        return jobBuilderFactory.get("xmlFileDemoJob")
                .start(xmlFileDemoStep())
                .build(); 
    } 
    @Bean
    public Step xmlFileDemoStep() {
        return stepBuilderFactory.get("xmlFileDemoStep")
                .<Customer,Customer>chunk(10)
                .reader(xmlFileDemoReader())
                .writer(xmlFileDemoWriter)
                .build();
    } 
    @Bean
    @StepScope
    public StaxEventItemReader<Customer> xmlFileDemoReader() {
        StaxEventItemReader<Customer> reader = new StaxEventItemReader<>(); 
        reader.setResource(new ClassPathResource("customer.xml"));
        reader.setFragmentRootElementName("customer");  
        XStreamMarshaller unMarshaller = new XStreamMarshaller();
        Map<String,Class> map = new HashMap<>();
        map.put("customer",Customer.class);
        unMarshaller.setAliases(map);
        reader.setUnmarshaller(unMarshaller);  
        return reader; 
    }
}

MultiResourceItemReader

从多个文件读取数据

@Configuration
public class MultipleFileDemoJobConfiguration {
    @Autowired
    private JobBuilderFactory jobBuilderFactory;
 
    @Autowired
    private StepBuilderFactory stepBuilderFactory;
 
    @Autowired
    @Qualifier("flatFileDemoWriter")
    private ItemWriter<? super Customer> flatFileDemoWriter;
 
    @Value("classpath*:/file*.csv")
    private Resource[] inputFiles;
 
    @Bean
    public Job multipleFileDemoJob(){
        return jobBuilderFactory.get("multipleFileDemoJob")
                .start(multipleFileDemoStep())
                .build(); 
    }
 
    @Bean
    public Step multipleFileDemoStep() {
        return stepBuilderFactory.get("multipleFileDemoStep")
                .<Customer,Customer>chunk(50)
                .reader(multipleResourceItemReader())
                .writer(flatFileDemoWriter)
                .build();
    }
 
    private MultiResourceItemReader<Customer> multipleResourceItemReader() { 
        MultiResourceItemReader<Customer> reader = new MultiResourceItemReader<>(); 
        reader.setDelegate(flatFileReader());
        reader.setResources(inputFiles); 
        return reader;
    }
 
    @Bean
    public FlatFileItemReader<Customer> flatFileReader() {
        FlatFileItemReader<Customer> reader = new FlatFileItemReader<>();
        reader.setResource(new ClassPathResource("customer.csv"));
       // reader.setLinesToSkip(1);
 
        DelimitedLineTokenizer tokenizer = new DelimitedLineTokenizer();
        tokenizer.setNames(new String[]{"id","firstName","lastName","birthdate"});
 
        DefaultLineMapper<Customer> lineMapper = new DefaultLineMapper<>();
        lineMapper.setLineTokenizer(tokenizer);
        lineMapper.setFieldSetMapper((fieldSet -> {
            return Customer.builder().id(fieldSet.readLong("id"))
                    .firstName(fieldSet.readString("firstName"))
                    .lastName(fieldSet.readString("lastName"))
                    .birthdate(fieldSet.readString("birthdate"))
                    .build();
        }));
        lineMapper.afterPropertiesSet(); 
        reader.setLineMapper(lineMapper); 
        return reader; 
    }
}

异常处理及重启机制

对于chunk-oriented step，Spring Batch提供了管理状态的工具。如何在一个步骤中管理状态是通过ItemStream接口为开发人员提供访问权限保持状态的组件。这里提到的这个组件是ExecutionContext实际上它是键值对的映射。map存储特定步骤的状态。该ExecutionContext使重启步骤成为可能，因为状态在JobRepository中持久存在。

执行期间出现错误时，最后一个状态将更新为JobRepository。下次作业运行时，最后一个状态将用于填充ExecutionContext然后

可以继续从上次离开的地方开始运行。

检查ItemStream接口：

将在步骤开始时调用open（）并执行ExecutionContext；

用DB填充值; update（）将在每个步骤或事务结束时调用，更新ExecutionContext;

完成所有数据块后调用close（）；

下面我们构造个例子

准备个cvs文件，在第33条数据，添加一条错误名字信息；当读取到这条数据时，抛出异常终止程序。

ItemReader测试代码

 
@Component("restartDemoReader")
public class RestartDemoReader implements ItemStreamReader<Customer> {  
    private Long curLine = 0L;
    private boolean restart = false; 
    private FlatFileItemReader<Customer> reader = new FlatFileItemReader<>(); 
    private ExecutionContext executionContext;
    RestartDemoReader
    public () {
        
        reader.setResource(new ClassPathResource("restartDemo.csv")); 
        DelimitedLineTokenizer tokenizer = new DelimitedLineTokenizer();
        tokenizer.setNames(new String[]{"id", "firstName", "lastName", "birthdate"});
 
        DefaultLineMapper<Customer> lineMapper = new DefaultLineMapper<>();
        lineMapper.setLineTokenizer(tokenizer);
        lineMapper.setFieldSetMapper((fieldSet -> {
            return Customer.builder().id(fieldSet.readLong("id"))
                    .firstName(fieldSet.readString("firstName"))
                    .lastName(fieldSet.readString("lastName"))
                    .birthdate(fieldSet.readString("birthdate"))
                    .build();
        }));
        lineMapper.afterPropertiesSet(); 
        reader.setLineMapper(lineMapper);
    }
 
    @Override
    public Customer read() throws Exception, UnexpectedInputException, ParseException,
            NonTransientResourceException { 
        Customer customer = null; 
        this.curLine++;
        //如果是重启，则从上一步读取的行数继续往下执行
        if (restart) {
            reader.setLinesToSkip(this.curLine.intValue()-1);
            restart = false;
            System.out.println("Start reading from line: " + this.curLine);
        }
 
        reader.open(this.executionContext); 
        customer = reader.read();
        //当匹配到wrongName时，显示抛出异常，终止程序
        if (customer != null) {
            if (customer.getFirstName().equals("wrongName"))
                throw new RuntimeException("Something wrong. Customer id: " + customer.getId());
        } else {
            curLine--;
        }
        return customer;
    }
 
    /**
     * 判断是否是重启job
     * @param executionContext
     * @throws ItemStreamException
     */
    @Override
    public void open(ExecutionContext executionContext) throws ItemStreamException {
        this.executionContext = executionContext;
        if (executionContext.containsKey("curLine")) {
            this.curLine = executionContext.getLong("curLine");
            this.restart = true;
        } else {
            this.curLine = 0L;
            executionContext.put("curLine", this.curLine.intValue());
        } 
    }
 
    @Override
    public void update(ExecutionContext executionContext) throws ItemStreamException {
        System.out.println("update curLine: " + this.curLine);
        executionContext.put("curLine", this.curLine); 
    }
 
    @Override
    public void close() throws ItemStreamException { 
    }
}

Job配置

以10条记录为一个批次，进行读取

@Configuration
public class RestartDemoJobConfiguration {
    @Autowired
    private JobBuilderFactory jobBuilderFactory;
 
    @Autowired
    private StepBuilderFactory stepBuilderFactory;
 
    @Autowired
    @Qualifier("flatFileDemoWriter")
    private ItemWriter<? super Customer> flatFileDemoWriter;
 
    @Autowired
    @Qualifier("restartDemoReader")
    private ItemReader<Customer> restartDemoReader;
 
    @Bean
    public Job restartDemoJob(){
        return jobBuilderFactory.get("restartDemoJob")
                .start(restartDemoStep())
                .build(); 
    }
 
    @Bean
    public Step restartDemoStep() {
        return stepBuilderFactory.get("restartDemoStep")
                .<Customer,Customer>chunk(10)
                .reader(restartDemoReader)
                .writer(flatFileDemoWriter)
                .build();
    }
}

当我们第一次执行时，程序在33行抛出异常异常，curline值是30；

这时，我们可以查询数据库 batch_step_excution表，发现curline值已经以键值对形式，持久化进数据库（上文以10条数据为一个批次；故33条数据异常时，curline值为30）

接下来，我们更新wrongName，再次执行程序；

程序会执行open方法，判断数据库step中map是否存在curline，如果存在，则是重跑，即读取curline，从该批次开始往下继续执行；

以上为个人经验，希望能给大家一个参考，也希望大家多多支持。

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