Spring Batch 如何自定义ItemReader

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 { 
    private int nextStudentIndex;
    private List 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 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 dbJdbcDemoWriter;
 
    @Autowired
    private DataSource dataSource;
 
    @Bean
    public Job DBJdbcDemoJob(){
        return jobBuilderFactory.get("DBJdbcDemoJob")
                .start(dbJdbcDemoStep())
                .build();
     }
 
    @Bean
    public Step dbJdbcDemoStep() {
        return stepBuilderFactory.get("dbJdbcDemoStep")
                .chunk(100)
                .reader(dbJdbcDemoReader())
                .writer(dbJdbcDemoWriter)
                .build();
    }
 
    @Bean
    @StepScope
    public JdbcPagingItemReader dbJdbcDemoReader() {
        JdbcPagingItemReader 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 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 {
    @Override
    public void write(List 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 flatFileDemoWriter; 
    @Bean
    public Job flatFileDemoJob(){
        return jobBuilderFactory.get("flatFileDemoJob")
                .start(flatFileDemoStep())
                .build(); 
    }
 
    @Bean
    public Step flatFileDemoStep() {
        return stepBuilderFactory.get("flatFileDemoStep")
                .chunk(100)
                .reader(flatFileDemoReader())
                .writer(flatFileDemoWriter)
                .build();
    }
 
    @Bean
    @StepScope
    public FlatFileItemReader flatFileDemoReader() {
        FlatFileItemReader 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 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 xmlFileDemoWriter; 
    @Bean
    public Job xmlFileDemoJob(){
        return jobBuilderFactory.get("xmlFileDemoJob")
                .start(xmlFileDemoStep())
                .build(); 
    } 
    @Bean
    public Step xmlFileDemoStep() {
        return stepBuilderFactory.get("xmlFileDemoStep")
                .chunk(10)
                .reader(xmlFileDemoReader())
                .writer(xmlFileDemoWriter)
                .build();
    } 
    @Bean
    @StepScope
    public StaxEventItemReader xmlFileDemoReader() {
        StaxEventItemReader reader = new StaxEventItemReader<>(); 
        reader.setResource(new ClassPathResource("customer.xml"));
        reader.setFragmentRootElementName("customer");  
        XStreamMarshaller unMarshaller = new XStreamMarshaller();
        Map 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 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")
                .chunk(50)
                .reader(multipleResourceItemReader())
                .writer(flatFileDemoWriter)
                .build();
    }
 
    private MultiResourceItemReader multipleResourceItemReader() { 
        MultiResourceItemReader reader = new MultiResourceItemReader<>(); 
        reader.setDelegate(flatFileReader());
        reader.setResources(inputFiles); 
        return reader;
    }
 
    @Bean
    public FlatFileItemReader flatFileReader() {
        FlatFileItemReader 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 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();

Spring Batch 如何自定义ItemReader_第1张图片

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。

Spring Batch 如何自定义ItemReader_第2张图片

ItemReader测试代码

 
@Component("restartDemoReader")
public class RestartDemoReader implements ItemStreamReader {  
    private Long curLine = 0L;
    private boolean restart = false; 
    private FlatFileItemReader 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 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 flatFileDemoWriter;
 
    @Autowired
    @Qualifier("restartDemoReader")
    private ItemReader restartDemoReader;
 
    @Bean
    public Job restartDemoJob(){
        return jobBuilderFactory.get("restartDemoJob")
                .start(restartDemoStep())
                .build(); 
    }
 
    @Bean
    public Step restartDemoStep() {
        return stepBuilderFactory.get("restartDemoStep")
                .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;

Spring Batch 如何自定义ItemReader_第3张图片

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)

Spring Batch 如何自定义ItemReader_第4张图片

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;

Spring Batch 如何自定义ItemReader_第5张图片

Spring Batch 如何自定义ItemReader_第6张图片

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脚本之家。

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