Spring Batch 如何自定義ItemReader

更新時間：2021年09月07日 16:08:35 作者：夢想畫家

這篇文章主要介紹了Spring Batch 如何自定義ItemReader的實現(xiàn)方式，具有很好的參考價值，希望對大家有所幫助。如有錯誤或未考慮完全的地方，望不吝賜教

Spring Batch 自定義ItemReader

Spring Batch支持各種數(shù)據(jù)輸入源，如文件、數(shù)據(jù)庫等。然而有時也會遇到一些默認不支持的數(shù)據(jù)源，這時我們則需要實現(xiàn)自己的數(shù)據(jù)源————自定義ItemReader。本文通過示例說明如何自定義ItemReader。

創(chuàng)建自定義ItemReader

創(chuàng)建自定義ItemReader需要下面兩個步驟：

創(chuàng)建一個實現(xiàn)ItemReader接口的類，并提供返回對象類型 T 作為類型參數(shù)。
按照下面規(guī)則實現(xiàn)ItemReader接口的T read()方法

read()方法如果存在下一個對象則返回，否則返回null。

下面我們自定義ItemReader，其返回在線測試課程的學(xué)生信息StuDto類型，為了減少復(fù)雜性，該數(shù)據(jù)存儲在內(nèi)存中。StuDto類是一個簡單數(shù)據(jù)傳輸對象，代碼如下：

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

下面參照一下步驟創(chuàng)建ItemReader:

創(chuàng)建InMemoryStudentReader 類
實現(xiàn)ItemReader接口，并設(shè)置返回對象類型為StuDto
類中增加List studentData 字段，其包括參加課程的學(xué)生信息
類中增加nextStudentIndex 字段，表示下一個StuDto對象的索引
增加私有initialize()方法，初始化學(xué)生信息并設(shè)置索引值為0
創(chuàng)建構(gòu)造函數(shù)并調(diào)用initialize方法
實現(xiàn)read()方法，包括下面規(guī)則：如果存在下一個學(xué)生，則返回StuDto對象并把索引加一。否則返回null。

InMemoryStudentReader 代碼如下：

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;
    }
}

創(chuàng)建好自定義ItemReader后，需要配置其作為bean讓Spring Batch Job使用。下面請看如何配置。

配置ItemReader Bean

配置類代碼如下：

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

需要增加@Configuration表明類為配置類，增加方法返回ItemReader類型，并增加@Bean注解，實現(xiàn)方法內(nèi)容————返回InMemoryStudentReader對象。

小結(jié)一下

本文通過示例說明如何自定義ItemReader，主要包括三個方面：

自定義ItemReader需實現(xiàn)ItemReader接口
實現(xiàn)ItemReader接口，需要指定返回類型作為類型參數(shù)(T)
實現(xiàn)接口方法read，如果存在下一個對象則返回，反之返回null

Spring Batch 之 ItemReader

重點介紹 ItemReader，如何從不同數(shù)據(jù)源讀取數(shù)據(jù)；以及異常處理及重啟機制。

JdbcPagingItemReader

從數(shù)據(jù)庫中讀取數(shù)據(jù)

@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); //批量讀取
        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不是本文介紹重點，此處舉例，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

從CVS文件中讀取數(shù)據(jù)

 
@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

從XML文件中讀取數(shù)據(jù)

@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

從多個文件讀取數(shù)據(jù)

@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; 
    }
}

異常處理及重啟機制

對于chunk-oriented step，Spring Batch提供了管理狀態(tài)的工具。如何在一個步驟中管理狀態(tài)是通過ItemStream接口為開發(fā)人員提供訪問權(quán)限保持狀態(tài)的組件。這里提到的這個組件是ExecutionContext實際上它是鍵值對的映射。map存儲特定步驟的狀態(tài)。該ExecutionContext使重啟步驟成為可能，因為狀態(tài)在JobRepository中持久存在。

執(zhí)行期間出現(xiàn)錯誤時，最后一個狀態(tài)將更新為JobRepository。下次作業(yè)運行時，最后一個狀態(tài)將用于填充ExecutionContext然后

可以繼續(xù)從上次離開的地方開始運行。

檢查ItemStream接口：

將在步驟開始時調(diào)用open（）并執(zhí)行ExecutionContext；

用DB填充值; update（）將在每個步驟或事務(wù)結(jié)束時調(diào)用，更新ExecutionContext;

完成所有數(shù)據(jù)塊后調(diào)用close（）；

下面我們構(gòu)造個例子

準備個cvs文件，在第33條數(shù)據(jù)，添加一條錯誤名字信息；當讀取到這條數(shù)據(jù)時，拋出異常終止程序。

ItemReader測試代碼

 
@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++;
        //如果是重啟，則從上一步讀取的行數(shù)繼續(xù)往下執(zhí)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();
        //當匹配到wrongName時，顯示拋出異常，終止程序
        if (customer != null) {
            if (customer.getFirstName().equals("wrongName"))
                throw new RuntimeException("Something wrong. Customer id: " + customer.getId());
        } else {
            curLine--;
        }
        return customer;
    }
 
    /**
     * 判斷是否是重啟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條記錄為一個批次，進行讀取

@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();
    }
}

當我們第一次執(zhí)行時，程序在33行拋出異常異常，curline值是30；